understanding blue green algae blooms in myall lakes nsw · 2015-03-06 · understanding blue green...

NSW Department of Infrastructure, Planning and Natural Resources

Understanding Blue Green AlgaeBlooms in Myall Lakes NSW.


As of the 2nd April 2003 the Department of Land and Water Conservation (DLWC) wasabolished by the NSW State Parliament and the Department of Sustainable Natural Resources(DSNR) established. As of the 29 th May 2003 the Department of Sustainable Natural Resourceswas abolished and replaced by the Department of Infrastructure, Planning and NaturalResource (DIPNR). Hence most references to DLWC have been changed to DIPNR. However asmany aspects of this project, including contracts between DLWC and Environment Australia,were undertaken prior to the 2nd April, reference is still made to DLWC in this document whereappropriate.


Understanding Blue Green AlgaeBlooms in Myall Lakes NSW.

Prepared by:Matthew Dasey, Joanne Wilson, NatashaRyan, Graham Carter, Nick Cook, SusanaRealica-Turner andEdited By:Matthew Dasey, Allan Raine,Natasha Ryan, Joanne Wilson and NickCook

Supported by:


Acknowledgments

This report was prepared with technical contributions from LeeBowling (CNR), Peter Scanes (EPA), Anna Redden (University ofNewcastle), Graham Harris (CSIRO) and Monika Muschal(CNR). Also DIPNR would like to thank the residents of theMyall Lakes area who greatly assisted in providing information onthe history of the lakes.

Published by:New South Wales Department of Infrastructure,Planning and Natural ResourcesHunter RegionJuly 2004NSW GovernmentISBN 0 7347 5498 1

Cover photographs – Myall Lakes. Taken by Joanne Wilson and Graham Carter

Understanding Blue Green Algae Blooms in Myall Lakes NSW.

NSW Department of Infrastructure, Planning, and Natural Resources

Contents Page

EXECUTIVE SUMMARY I

1. INTRODUCTION 1

1.1 Background 11.2 Scope and Objectives of the Coast and Clean Seas Project 31.3 Myall Lakes in Comparison to other Australian coastal lakes and estuaries 4

1.3.1 Classification of Coastal Waterways 41.3.2 Classification of the health and status of coastal waterways in Australia 4

1.4 Nutrient dynamics in estuaries and coastal lakes 71.4.1 The sources of nutrients 71.4.2 Nutrient limitations, cycling and algal production 81.4.3 Response of lakes and estuaries to nutrient loads 9

2. CHARACTERISTICS OF MYALL LAKES AND ITS CACTCHMENT 11

2.1 Location of Study Area 112.2 Characteristics of the Myall Lakes region 11

2.2.1 Climate 122.2.2 Geology and soils 142.2.3 Preliminary geomorphic status of the Myall River catchment 152.2.4 Settlement History and Landuse 182.2.5 Human Settlement 19

2.3 Characteristics of the Myall Lakes System 202.3.1 Geography 202.3.2 Lake Flushing 202.3.3 Lake Structure and Bathometry 212.3.4 Sedimentology of the Broadwater, Myall Lakes NSW 232.3.5 Benthic Nutrient Fluxes in Bombah Broadwater, Myall Lakes 242.3.6 Groundwater quality 26

2.3.6.1 Groundwater Electrical Conductivity 282.3.6.2 Groundwater pH 292.3.6.3 Groundwater Chemical composition 292.3.6.4 Indications of Possible sewage contamination 30

2.3.6.4.1 Faecal Bacteria 302.3.6.4.2 Nutrients 302.3.6.4.3 Nutrient Trends versus Water Level Trends 322.3.6.4.4 Nutrients and Park Occupancy 322.3.3.4.5 Synopsis 33

3. NUIRIENT SOURCES TO MYALL LAKES 35

3.1 Catchment nutrient inputs to Myall Lakes 353.1.1 Catchment Management Support System Modelling 35

3.1.1.1 Comparison of loads arising in Myall Lake sub-catchments 363.1.1.2 CMSS Estimates of historical and contemporary annual nutrient loads 373.1.1.3 CMSS Estimates of nutrient source arising from different land uses 38

3.1.2 Estimates if nutrient load from River volume 393.1.3 Measured Nutrient Exports from the Catchment - autosampler results 393.1.4 Results from Water Quality Monitoring in the Myall River 403.1.5 Atmospheric Nutrient Contributions 433.1.6 Potential nutrient contributions from National Park visitor sewage waste 43



3.1.7 Estimated Phosphorus load from Groundwater inflows 433.1.8 Estimate of Myall Lakes System nutrient loading per unit lake surface area 44

4. PHYTOPLANKTON ABUNDANCE AND DISTRIBUTION 45

4.1 Background 454.1.1 Phytoplankton community as an indicator of estuarine health 45

4.1.1.1 Changes in phytoplankton community and ecological succession 464.1.2 Some Characteristics of Blue-Green Algae 48

4.1.2.1 Adaptations of Blue-Green Algae 484.1.2.2 Ambient conditions that enhance Blue-Green algal growth 494.1.2.3 Human health implications of Blue-Green algae 50

4.2 Methods 514.2.1 Aims of the monitoring study 514.2.2 Algal sampling and analysis 514.2.3 Data Analyses and presentations 52

4.3 Results 534.3.1 Spatial Distributions of Blue-Green Algae 534.3.2 Blue-Green Algal community change and succession 55

4.3.2.1 Multivariate analysis of temporal and spatial trends in the Blue-Green AlgaeCommunity 554.3.2.2 Phase 1 - Blue-Green Algal Bloom 564.3.2.3 Phase 2 - Blue-Green Algal Bloom 574.3.2.4 Phase 3 - Blue-Green Algal Bloom 58

4.3.3 The response of algal community composition to changing conductivity 594.3.4 Descriptions of phytoplanktonic community succession in Myall Lakes 62

4.3.4.1 Upper Myall Rivermouth 634.3.4.2 Bombah Braodwater 634.3.4.3Two-Mile and Boolambayte Lakes 644.3.4.4 Myall Lake 664.3.4.5 Some observed patterns of phytoplankton diversity and abundance 67

4.4 Discussion 684.4.1 The role of conductivity in algal community composition change 684.4.2 Patterns of nutrient concentration and the algal community in Myall Lakes 684.4.3 Other factors influencing the composition of Blue-Green Algae communities 70

5. WATER QUALITY 72

5.1 Water Nutrients 725.1.1 Introduction 725.1.2 Methods 73

5.1.2.1 Rainfall 735.1.2.2 Water nutrient analyses 735.1.2.3 Near-Benthic Water collection 745.1.2.4 Interpreting nutrient data against ANZECC and ARMCANZ guidelines 745.1.2.5 Data consolidation and presentation 75

5.1.3 Results 765.1.3.1 Rainfall 775.1.3.2 Total Phosphorus 785.1.3.3 Soluble Reactive Phosphorus 785.1.3.4 Total Nitrogen 805.1.3.5 Ammonium 815.1.3.6 Nitrate/Nitrite 815.1.3.7 Chlorophyll a 815.1.3.8 Near-Benthic Water Collection 92



5.1.4 Discussion 935.1.4.1 Temporal and spatial patterns of nutrient distribution 935.1.4.2 N Near-Benthic Water Collection 95

5.2 Nitrogen Stable Isotope signatures of Aquatic Plants 965.2.1 Introduction 965.2.2 Methods 975.2.3 Results 995.2.4 Discussion 100

5.3 Physico-chemical parameters 1005.3.1 Introduction 1005.3.2 Methods 1015.3.3 Results 102

5.3.3.1 Stratification 1105.3.3.2 Light availability 112

5.3.4 Discussion Physico-chemical water quality 116

6. AQUATIC VEGETATION AND LAKE HABITAT 119

6.1 Background 1196.1.1 Vegetation 1196.1.2 Lakebed sediments 120

6.2 Methods6.2.1 Vegetation assessment method 1216.2.2 Lakebed assessment method 122

6.3 Results 1236.3.1 Vegetation 1236.3.2 Types of aquatic plants found in Myall Lakes 1246.3.3 Spatial Distribution of plants in Myall Lakes 1316.3.4 Temporal Change in the Distribution of plants in Myall Lakes 133

6.3.4.1 Najas marina and Charophytes - Annual growth cycles 1336.3.4.2 Vallisneria gigantea - Broadwater die-off 1346.3.4.3 Potamogeton perfoliatus - Widespread colonisation 134

6.3.5 Benthic Survey - Results and Discussion 1346.3.5.1 Percent Total Organic Carbon (TOC) 1356.3.5.2 Total Nitrogen (TN) 1356.3.5.3 Total Phosphorus (TP) 1356.3.5.4 Total Sulphur (TS) 1366.3.5.5 Grainsize Analysis 1366.3.5.6 Benthic Microcystis sp 139

6.4 Discussion 1406.4.1 Vegetation 1406.4.2 Benthic Nutrient Content 1436.4.3 General Discussion 143

7. SYNTHESIS OF THE DATA 145

7.1 What are the physical and biological conditions/processes, which contribute toBlue-Green Algal blooms in Myall Lakes 1457.2 What are the relative contributions of nutrient sources to algal growth in the lakes? 149

7.2.1 The role of nutrients in algal growth 1497.2.2 Sources of nutrients to Myall Lakes 149

7.2.2.1 Rainfall 1497.2.2.2 Groundwater 1497.2.2.3 Catchment Inflows 1507.2.2.4 Nutrient recycling within the lakes 150



7.2.3 Summary of nutrient source data 1527.3 What is the nutrient status of Myall Lakes 152

7.3.1 Techniques to assess nutrient status 1537.3.2 Assessing the nutrient status of Myall Lakes 1547.3.3 Risks due to increasing nutrients 158

7.4 Supporting the development of effective management strategies to reducecatchment loads 159

7.4.1 Regional Strategic Focus: Lower North Coast Catchment Blueprint 1597.4.2 Local Catchment Level: Myall Community Catchment Plan 1607.4.3 Specific Initiatives: Dairy Industry trials to investigate effectiveness of buffer strips 161

7.5 Developing pro-active assessment protocols to assist in the management of futurealgal blooms 1657.6 Myall Lakes - Where to from here? 166

7.6.1 Continued Monitoring in Myall Lakes and its Catchment 1667.6.2 Additional ongoing investigations 1677.6.3 Future Studies 168

8. REFERENCES 170

9. APPENDICES 176

Executive summary Understanding Blue Green Algae Blooms in Myall Lakes NSW

NSW Department of Infrastructure, Planning and Natural Resources I

Executive summary

Myall Lakes is one of the largest coastal lake systems in New South Wales boasting over ten

thousand hectares of waterways set wholly within the Myall Lakes National Park. The Myall

Lakes system comprises a series of lakes including the Bombah Broadwater (lower lake),

Two Mile and Boolambayte Lakes (mid-lakes) and Myall Lake (upper lake). Feeding this lake

system is a catchment area of 78,000 hectares. The Myall and Crawford rivers are the main

tributaries to the lake system, feeding into Bombah Broadwater, while Boolambayte Creek

also supplies fresh water. The Lower Myall River connects this unique waterbody to the

ocean, allowing saltwater exchange from Port Stephens. Myall Lakes has significant

environmental and cultural value to the local, national and international community. The lake

system is recognised internationally under the Ramsar Convention as an important wetland,

and Myall Lakes National Park is a popular tourist destination for camping, bushwalking,

fishing, boating and water sports. A healthy lake system is integral to the culture and

economy of the local area.

In early 1999 Myall Lakes began to exhibit major signs of a natural system in trouble when a

large, toxic blue-green algae bloom formed in the lower section of the lakes. Blue-green algae

are a type of bacteria that act like plants by using light for photosynthesis. When conditions

are ideal they can multiply at a prolific rate resulting in a bloom. Potentially harmful algal

scums accumulated on the shores of the lake including at many popular camping areas. The

bloom persisted on-and-off until April 2001 having a major impact on the local community –

tourist numbers dropped and the lakes were intermittently closed to commercial and

recreational fishing. Blue-green algal blooms have continued to occur in the lakes since mid

2001, although not as severely as those experienced in 1999.

The initial algal bloom in 1999 left the Myall Lakes community extremely concerned about

the future of their unique natural asset. The State Government responded to these concerns by

initiating the ‘Monitoring Blue-Green Algae in Myall Lakes’ project - a partnership between

the then Department of Land and Water Conservation (DLWC; now Department of

Infrastructure, Planning, and Natural Resources [DIPNR]) and the NSW National Parks and

Wildlife Service (NPWS: now part of the Department of Environment and Conservation

[DEC]) with funding from the Federal Government’s Coasts and Clean Seas program. The

project was designed to:

? understand the combination of factors that cause algal blooms in the lakes;

? determine the overall health of the Myall Lakes system; and


NSW Department of Infrastructure, Planning and Natural Resources II

? predict the likelihood that they would occur again.

This information was considered vital to ensure future resources could be effectively targeted

to manage the lakes system, and the impact of possible future algal blooms.

Information collected during the study (2001–2002) was combined with information collected

prior to 2001, and from recent catchment studies. Interpretation of the many sources of

information was complex, and in many cases, characteristics of both eutrophic and

mesotrophic environments occurred simultaneously or sequentially in the same area.

However, a picture has emerged of the major nutrient sources, temporal and spatial patterns in

physical and ecological characteristics of Myall Lakes, and the likelihood of toxigenic algal

blooms occurring in the future.

The period over which information was available (1999-2002) encompassed both above and

below average rainfall conditions, and extended throughout the entire Myall Lakes region.

During the period of the project (2001-2002), below average rainfall was experienced, and no

toxigenic algal blooms occurred. This study highlighted the naturally high variability in

physical and ecological characteristics among the interconnected lakes and between ‘wet’ and

‘dry’ periods. During the study a benthic organic microalgal layer was discovered over much

of the bed of Myall Lake and some of the mid-lakes region. The role this layer plays in the

ecology of the lake is yet to be determined, though some speculation is made in this report.

The study showed that catchment runoff from the Upper Myall River is currently the most

important source of ‘new’ nutrients contributing to the formation of toxigenic algal blooms in

Myall Lakes (noting that a significant amount of nutrient is already ‘stored’ within the lake

sediments). Due to long flushing times, the lake acts as an effective trap for nutrients, organic

matter and sediments and is therefore highly vulnerable to increased inputs from the

catchment. The naturally low flushing also results in increased importance of the processing

of organic matter and nutrients by processes occurring in the lake sediments.

The status of the three main regions of the lake system is discussed separately below.

Broadwater

The occurrence of toxigenic algal blooms in the Broadwater in 1999 alerted the community

and natural resource managers to the potentially eutrophic status of this waterway.

Investigations during the project showed that while some characteristics of the Broadwater are

generally indicative of eutrophication, others are typical of mesotrophic waterways. Most

signs of eutrophication in the Broadwater are associated with periods of high inflow when a


NSW Department of Infrastructure, Planning and Natural Resources III

large proportion of the total nutrient load is delivered to the system. At times of low inflow, it

appears the area is able to ‘recover’ to a mesotrophic state.

Evidence for eutrophication of the Broadwater includes high loads of nutrients from the

catchment, long flushing time, the occurrence of toxigenic blue-green algal blooms, low water

clarity, sometimes high concentrations of phosphorus and nitrogen in the water column, the

presence of filamentous algal species in macrophyte beds, restriction of aquatic plants to

shallow water, and low denitrification rates in muddy sediments. However, the presence of

extensive beds of perennial macrophytes, good water quality during dry periods and high

denitrification in shallow sandy sediments indicate a mesotrophic status.

It appears then that at most times, the lake is ‘healthy’ but switches to a eutrophic state in

response to large inflows from the catchment. The extended period of above average rainfall

that occurred prior to April 1999 created favourable conditions in the Broadwater for

toxigenic blue-green algal blooms. Large inflows of freshwater from the catchment reduced

the salinity of the Upper Myall Lake and Broadwater to that of a freshwater system, carried

high loads of nutrients and sediment, and caused increased turbidity. It appears this

combination of conditions, particularly the extremely low salinity, occur infrequently in the

Broadwater and are dependant on the duration and intensity of rainfall in the catchment of the

Upper Myall River.

The flushing time of the Broadwater is long relative to other coastal lakes in NSW, and

therefore it will act as an effective sink for nutrients, organic matter and suspended sediments.

However, compared to other regions within Myall Lakes, it is most influenced by both

catchment inflows and tidal exchange. Therefore, while it receives the highest nutrient and

organic load from the catchment, a small amount will be lost through flushing. Also, the

relative influence of saline intrusion and freshwater inflows result in significant, long term

changes in salinity related to wet and dry rather than seasonal cycles. For example, over the

period of this study, salinity ranged between 1 and 18 mS/cm.

The Upper Myall River is a significant source of nutrients to the Broadwater. Levels of

phosphorus in the water column at the mouth of the Upper Myall River are typically high in

both wet and dry periods. This indicates that the Upper Myall River is an important source of

Phosphorous to the Broadwater, even in dry conditions when flows are low.

The Broadwater is naturally turbid due to the deposition of fine particles carried in the Upper

Myall River. These settle rapidly once riverine waters meet the slower moving lake waters.

Strong winds and the shallow nature of the Broadwater results in frequent resuspension of this


NSW Department of Infrastructure, Planning and Natural Resources IV

fine material. Naturally turbid conditions restrict the growth of macrophytes to the shallower

areas of the lake around 1.5m depth or less. Therefore, increases in turbidity would further

restrict the distribution of macrophytes in the Broadwater to the shallow margins of the lake.

The macrophyte assemblage in the Broadwater is composed of species typical of estuarine to

brackish environments. It includes perennial macrophytes (Vallisineria, and Ruppia); and

loosely attached macroalgal assemblages (Gracillaria and Enteromorpha). These

macrophytes play a number of very important roles as primary producers, physical habitat for

fish and invertebrates, absorbing nutrients, stabilising sediments, and oxygenating the water

column. Many macrophyte species are sensitive to changes in nutrient loads or ratios, and

reduction in area or changes in species composition can be an indicator of decline. The

presence of filamentous algae amongst some areas of macrophyte beds in the Broadwater is

likely to be a sign of increasing eutrophication.

The sediment distribution and bathometry of the Broadwater is typical of other coastal lakes.

Shallow banks are composed of sandy sediments, which slope steeply to deeper areas

characterised by fine muddy sediments. Preliminary studies showed that carbon, nitrogen and

phosphorus content in the sediments were similar to other coastal lakes in NSW. While these

nutrients are generally bound tightly to sediments, studies in the Broadwater showed that

nutrients stored in muddy sediments may be released into the water column as ammonium or

nitrate, fuelling further algal growth. This release of inorganic nutrients to the water column

is enhanced under low oxygen conditions. Low oxygen near the sediments are likely to occur

in the Broadwater after inflows deliver organic matter and freshwater. This increases the

oxygen demand of the sediments due to decomposition of organic matter, and stratification

due to salinity differences. This often results in the bottom layer becoming anoxic as the

oxygen is not replaced by photosynthetic activity or wind mixing.

Myall Lake

Of all three lakes, Myall Lake appears to be the most ‘healthy’ but also the most sensitive to

any increases in nutrient loads. Myall Lake has good water clarity, low nutrient load (in terms

of delivery of ‘new’ nutrients from the catchment, particularly phosphorus [P]), generally low

water column nutrient concentrations, and diverse macrophyte assemblages. These

characteristics are indicative of an oligotrophic system but the dominance of green and small

blue-green algal species in the phytoplankton, and the highly organic content of the bed of the

lake are signs of some level of nutrient enrichment. However, toxigenic blue-green algal

species such as Anabaena and Microcystis have not been recorded in the water column of


NSW Department of Infrastructure, Planning and Natural Resources V

Myall Lake during the study period. The blue-green algal alerts were triggered by high

biovolumes of other non-toxigenic species of blue-green algae.

Myall Lake has no major freshwater inflows and is furthest from the influence of tidal

flushing. Consequently it has an extremely long flushing time which makes it highly sensitive

to any increase in nutrient loads. It also results in an extremely stable water body. The salinity

of the lake is very low and movement of saline water from the Broadwater only has a very

small influence on the Lake. Salinity changes are very small and occur over the time scale of

years. The water column is well mixed and remains clear throughout the year. Stratification

was not recorded during this study due to the lack of freshwater inflows. Therefore conditions

which favoured the development of toxigenic blue-green algal blooms in the Broadwater did

not occur in Myall Lake.

Any significant increase in the nutrient load has the potential to cause symptoms of

eutrophication, including the development of toxigenic algal blooms. The current

characteristics and composition of the phytoplankton and macrophyte communities provide

some indication as to the likely consequences of increased nutrients, particularly phosphorus.

The phytoplankton community is dominated by small blue-green and green algal species,

which are good competitors in low phosphorus environments. Diatoms are unlikely to become

a major part of the community, as there are indications of silica limitation in this part of the

lake. Silica is an essential requirement for diatom growth and values are very low in Myall

Lake. In addition, while the macrophyte community is diverse, it is dominated by

macrophyte species such as Chara and Najas. These species have a highly seasonal growth

pattern and form extensive beds which cover up to 80% of Myall Lake during summer and

autumn, and then die off over winter. At present, these macrophytes grow to the bottom of the

deeper areas of the lake due to the good water clarity and high light penetration. Species such

as Chara and Najas will only grow in low phosphorus environments. Increases in P are likely

to result in a switch from a clear, macrophyte dominated community to a more turbid system

dominated by phytoplankton species.

During this study, phosphorus concentrations in the water were very low. Values for total

nitrogen were consistently high throughout the study, although it is likely that approximately

80% of the total nitrogen is in a form (dissolved organic nitrogen) not readily bioavailable to

algae. These results probably reflect the lack of riverine inflows and the recycling of organic

matter and nutrients within this essentially closed system. The seasonal growth of

macrophytes is likely to utilise a large amount of nutrients during periods favourable for algal

growth (high light and temperature). The decay of large quantities of macrophytes may have

contributed to the high nitrogen and carbon content on the bed of this lake. The nutrients in


NSW Department of Infrastructure, Planning and Natural Resources VI

the sediments and organic layer are likely to play an important role in the nutrient cycling of

Myall Lake due to its reduced flushing. Further investigations are required to determine

whether nutrients are released into the water column, and the conditions that may favour this.

This organic layer also contains a benthic Microcystis species that has not been detected in

water column samples. This benthic algal layer may be playing an important role in absorbing

nutrients generated in the sediments through remineralisation of organic matter before they

reach the water column. It is also suspected that the benthic algal layer may have a major

influence on the type of aquatic plants present in Myall Lake. It is speculated that the benthic

layer does not allow the establishment of most species, due to its mucous-like character, and

that only Najas has the ability to establish and grow within it.

Mid-Lakes

The Mid-Lakes region encompasses Boolambayte and Two-Mile Lakes. This region receives

a small riverine inflow from Boolambayte Creek and also exchanges water with the

Broadwater at Bombah Pt and Myall Lake at Violet Hill. Not surprisingly, the characteristics

of this region are intermediate between the Broadwater and Myall Lake. Two Mile Lake is

more similar to the Broadwater, while Boolambayte Lake shares characteristics similar to

Myall Lake. While the nutrient loads to this region are smaller than to the Broadwater, the

flushing time is longer and therefore this area is more susceptible to nutrient inputs.

Two Mile Lake shows signs of eutrophication similar to that of the Broadwater, particularly

during wet weather. It has experienced toxigenic algal blooms, and elevated nutrient

concentrations. However, it is less turbid than the Broadwater and has healthy and diverse

macrophyte communities. Macrophytes are composed of both perennial and ephemeral

species, especially in the southern part of the lake. There, extensive sandy areas support dense

beds of perennial species to a depth of 2m. There was some growth of the ephemeral species

Najas, over summer, but growth was not as extensive as in Myall Lake. This may be due to

competition for nutrients with other macrophyte species, and reduced water clarity which

restricted the development of Najas to shallower areas. Also, higher concentrations of

phosphorus which occur in Two Mile Lake compared to Myall Lake may not be suitable for

the growth of some species such as Chara.

Water quality of Two Mile Lake reflects the exchange with and proximity to the Broadwater.

The southern part of this lake had characteristics similar to the Broadwater i.e. higher salinity

and phosphorus and lower nitrogen, while the northern part was more similar to Myall and

Boolambayte Lakes. The conditions, which favoured the development of toxigenic algal


NSW Department of Infrastructure, Planning and Natural Resources VII

blooms in the Broadwater also, occurred in Two Mile Lake. As such these occurred

concurrently in the two lakes.

The substrate and bathometry of Two Mile Lake is composed of extensive shallow sandy beds

covered in macrophytes, with steep drop offs to muddy, organic areas up to 3 m deep. High

concentrations of ammonium in waters close to the bottom in deeper areas highlights the

possibility that remineralisation of organic matter may be returning ammonium to the water

column.

Boolambayte Lake receives inflows from Boolambayte Creek. Given the longer flushing time

of this Lake compared to Two Mile and Broadwater, it is likely that this area is the most

susceptible to increased nutrient loads from the catchment. Currently, Boolambayte Lake

shows characteristics similar to Myall Lake. The lake is clear, and is dominated by ephemeral

macrophyte species Najas, and numbers of toxigenic algal species remained low even during

blooms in Two Mile Lake. Salinity is generally low but shows a greater range than Myall

Lake. Nutrient concentrations are similar to Myall Lake with generally low phosphorus, and

higher nitrogen. The phytoplankton assemblage is dominated by small blue-green and green

algal species with Violet Hill Passage recording some of the highest biovolumes of non-

toxigenic blue-green algae. These non-toxigenic blue-green algae have triggered alerts after

the toxigenic algal blooms disappeared from the Broadwater and Two Mile Lakes.

Boolambayte Lake is relatively shallow and extensive areas of the bed are covered in the

organic microalgal layer. The characteristics of this material are similar to that of Myall Lake

although values for organic carbon and nitrogen content were lower than in Myall, but higher

than the rest of the lake.

Synopsis

The study has highlighted that for toxic blue green algae blooms to form, a number of factors

need to occur at the same time. The main factors include:

? freshwater inflows (floods) from the upper Myall River which are large enough to

displace saline water in the Broadwater (so that salinity levels are at least lower than

2mS/cm);

? turbid water which gives toxic blue-greens a competitive advantage over other

phytoplankton species; and

? high levels of nutrients to fuel algal growth (including those delivered by flooding and

potentially those released from sediments).


NSW Department of Infrastructure, Planning and Natural Resources VIII

It is likely that the conditions, which were responsible for the blooms of 1999, will occur

again, and therefore it is expected that toxic blue green algal blooms will occur in future.

Because the upper Myall River directly discharges freshwater into the Broadwater it is likely

that the conditions required for bloom formation will be limited to this area, and the adjacent

Two-mile Lake, in the short to medium term. The project has shown that a good indicator for

the potential of a bloom to form in the Broadwater is when salinity levels fall below 2mS/cm

(and conditions become more or less eutrophic).

The Broadwater’s link to Port Stephens (and hence tidal waters) ultimately increases salinity

levels (following freshwater inflows) to a point where toxic blue green algae species cannot

survive (and conditions return to mesotrophic).

The study has highlighted that the relative isolation of Myall Lake from direct freshwater

inflows from the catchment and saline inflows from the estuary, has created a stable

environment where toxic algal blooms are unlikely to occur. It has also highlighted that Myall

Lake would be very sensitive to any sustained increase in nutrient levels.

The study has found that there is no ‘quick-fix’ to remove toxic algal blooms once they form.

It also recognises that the cumulative impact of increased nutrient delivery from the

catchment (mainly during flood flows) over time may have led to increased sediment /

nutrient levels. As such, the main management action that can reduce the likelihood of

blooms occurring over the long-term is to reduce the amount of nutrient delivered to the lakes

from the catchment during flood events. Catchment management should be targeted at those

landuse activities that deliver the highest nutrient levels relative to the area they occupy.

Chapter 1, Introduction. Understanding Blue Green Algae Blooms in Myall Lakes NSW.

NSW Department of Infrastructure, Planning, and Natural Resources 1

1. Introduction.

1.1. BACKGROUND.

The Myall Lakes system is a series of interconnected fresh to brackish coastal lakes that are

central to the Myall Lakes National Park. The Myall Lakes represent the only remaining

example of a large coastal brackish lake on the NSW coast that has not been greatly modified

by human activities and only one of its type in the Manning shelf bioregion (NPWS 2002).

The outstanding natural and cultural values of this lake system have been recognised

internationally, with Myall Lakes National Park being listed as a Ramsar Wetland of

International Importance (NPWS 2002).

In early April 1999, a bloom of harmful blue green algae (Anabaena spp) was reported in the

Broadwater and lower section of Boolambayte Lake (anecdotal evidence suggests that a small

outbreak could have formed some time earlier in 1999). The bloom extended from Bombah

Broadwater through to Korsmans Landing, with scums forming at foreshore sites including

popular camping areas. In response, the Manning/Karuah/Great Lakes Regional Algae

Coordinating Committee (MKGLRACC) placed the lower section of Myall Lakes up to

Korsmans Landing on ‘algal high alert’ in accordance with the Manning/Karuah/Great Lakes

Regional Algal Contingency Plan. Under this protocol, alerts (warnings and/or closures) are

placed on certain locations to minimise human contact with harmful algae.

Since the initial bloom in 1999, numerous warnings have been issued and lifted in different

areas of the lakes in accordance with the Contingency Plan, with the final warning on the

Bombah Broadwater being lifted in April 2001. In June 2000, there was a sharp decline in the

toxin producing species such as Anabaena circinalis and Microcystis aeruginosa in the

Broadwater, and an increase in non-toxin producing species such as Chroococcus sp and

Merismopedia sp (details of algal dynamics are presented in Chapter 4).

However, Myall Lake and the upper reaches of Boolambayte Lake have experienced repeated

blue-green algal blooms, composed predominantly of Chroococcus, over the past 2 years, in

particular around the Neranie area. This area of Myall Lakes is the least flushed part of the

whole system (see Chapter 2) and is more freshwater in its ecology. The last ‘high alert’ for

this area was lifted in April 2002. However, a high alert was issued for Violet Hill in

November 2002 in response to potentially harmful levels of blue green algae (Chroococcus)

being detected. The high alert status was still current in early February 2003.



The occurrence of harmful blue green algal blooms has often been associated with

eutrophication (nutrient enrichment) of inland and coastal waterways in Australia and

overseas (Livingston 2001). Prior to the recent blue green algal blooms Myall Lakes was

considered a near-pristine coastal lake and there was little information on the ecology and

nutrient status of the lakes. Atkinson et al (1981) highlighted the vulnerability of the system to

eutrophication, although recent cursory assessments considered the lakes to be in good

condition (MHL 1998). Therefore the occurrence of blooms was unexpected, and it was

difficult to move beyond speculation of the cause of the blooms, or whether blue green algal

blooms had occurred in the lakes prior to 1999.

The sustained blue-green algae blooms within Myall Lakes focused attention not only on the

environmental conditions within the lake itself, but also on the surrounding catchment area

which is the primary source of most water column nutrients. As a result, the then NSW

Department of Land and Water Conservation (now Department of Infrastructure, Planning

and Natural Resources [DIPNR]1) and NSW National Parks and Wildlife Service (NPWS;

now part of the Department of Environment and Conservation [DEC]2) initiated the Myall

Lakes Catchment Investigation to provide a basic assessment of catchment water quality and

some of nutrient cycling processes within the lake system. As part of this assessment, a long-

term monitoring program was also set up to monitor phytoplankton within the lakes so that

the distribution of blue-green algal blooms within the system could be determined and to

assess risk to public health as required under the RACC protocols. Funding was also made

available for additional studies. These included; measuring nutrient loads from the catchment

in rain events, using an autosampler stationed at Bulahdelah; monthly monitoring of nutrient

concentrations at a number of sites in the Upper Myall River; and measurement of the fluxes

of nutrient from the lake sediments to the water column.

In 2001, further funding was obtained through the Federal Government’s Natural Heritage

Trust Coasts and Clean Seas (CCS) program for the project ‘Monitoring Blue Green Algal

Blooms in Myall Lakes’ to investigate the ecology of the lakes and assess its nutrient status.

This information was required to identify the factors that may have led to the blooms, assess

the likelihood of future blooms, and draft informed management options to reduce the risk of

this occurring.

1 Note that the project was undertaken by the Department of Land and Water Conservation (DLWC).DLWC is now known as the Department of Infrastructure, Planning, and Natural Resources (DIPNR)and is hence referred to as such in the body of this report.2 Note that subsequent to the project being finalised the Department of Environment and Conservationwas established bringing four agencies together into a single department that includes the NationalParks and Wildlife Service.



1.2. SCOPE AND OBJECTIVES OF THE COASTS AND CLEANS SEAS PROJECT.

The Coasts and Clean Seas project ‘Monitoring Blue Green Algae in Myall Lakes’ was

developed as a partnership between DIPNR and NPWS. The monitoring project was initiated

in September 2001. The main objectives of the project were to:

? Determine the physical and biological conditions and processes that contributed to the

occurrence of blue green algal blooms in Myall Lakes;

? Assess the relative contribution of different sources of nutrients to algal growth in Myall

Lakes;

? Assess the nutrient status of Myall Lakes by comparing the relative biomass of different

primary producers (phytoplankton, benthic microalgae, macroalgae, seagrasses /

macrophytes) in Myall Lakes;

? Obtain information to support the development and implementation of effective

management strategies to reduce catchment nutrient loads; and

? Develop pro-active assessment protocols to assist in the management of future algal

blooms.

The project was an ambitious one at the outset and while the objectives of the project have

been met to varying degrees. For example plant biomass investigations were replaced with a

study of plant distribution after the discovery of a layer of Gyttja diverted resources to its

investigation there is still much to learn about nutrient dynamics and lake ecology. The results

of the monitoring program, combined with additional work carried out prior to and since the

commencement of the project, provide information on fundamental ecological processes

affecting nutrient dynamics and phytoplankton growth within Myall Lakes. Findings of the

project will also be incorporated into existing management plans and processes including the:

? Plan of Management for Myall Lakes National Park and RAMSAR Site Management,

? Lower North Coast Catchment Management Blueprint.

? Myall Lakes Community Catchment Plan,

This report details the results of the CCS project and provides a starting point for promoting a

better understanding of the lakes’ dynamics and ecology.



1.3. MYALL LAKES IN COMPARISON TO OTHER AUSTRALIAN COASTALLAKES AND ESTUARIES.

1.3.1. Classification of Coastal Waterways.

Each coastal waterways is a unique ecosystem with characteristics (eg. salinity, age, size,

catchment size, flushing time) that can make it quite distinct in character even from adjacent

waterways. The biological communities in these waterways can likewise also be unique, so it

is difficult to describe and quantify the health and character of a waterway relative to others,

based on the resident ecological assemblages. There have been recent attempts to standardise

the classification and health of estuaries in Australia.

Roy et al. (2001) has published a classification for south east Australian estuaries. Three main

types of estuary are recognised in NSW. They are:

1) Tide-dominated, drowned river valleys,

2) Wave-dominated, barrier estuary and,

3) Intermittently Closed and Open Coastal Lakes and Lagoons (ICOLLs).

The latter two estuary types are the most common in NSW and often have water residence

times3 of greater than one year (Roy et al., 2001). These systems are generally shallow, with

mixing achieved predominantly through wind-driven water circulation (Roy et al., 2001).

The Myall Lakes system is described as a brackish barrier estuary (Roy et al., 2001) and has

an estimated flushing time of between 400 and 800 days (MHL 1998; Atkinson et al., 1981).

1.3.2 Classification of the health and status of coastal waterways in Australia.

Estuaries are the end point for the runoff from coastal catchments. Due to their small

entrances in proportion to their volume and diminished tidal range, coastal lakes and lagoons

often act as sinks for inputs from their catchments. The nutrient trapping ability of coastal

lakes makes these locations very productive natural systems, and crucial components of

coastal ecology. Conversely, the ability of these estuaries and coastal lakes to trap nutrients

makes them especially prone to eutrophication and sedimentation.

Rapid declines in lake health resulting in loss of habitat and biodiversity may shortly follow

excessive nutrient loadings. Therefore, because coastal lakes are especially vulnerable, much

3 Water residence time refers to the estimated time it takes for the water in a given area to be fullyreplaced.



of the recent effort has been applied to rapidly identify the waterways most likely to

experience environmental decline. Two recent initiatives have provided assessments of the

health or condition of estuaries Australia wide, and of coastal lakes in NSW. These are:

1. National Land and Water Resources Audit (NLWRA) -a nationwide estuarine assessment,

2. Healthy Rivers Commission (HRC) Inquiry into Coastal Lakes –focussing on the health

and management of coastal lakes in NSW.

NLWRA - Estuarine Assessment, 2000.

The NLWRA assessed the health of 970 estuaries Australia-wide and classified them into 4

categories of Near Pristine, Largely Unmodified, Modified and Severely Modified. The initial

condition assessment results found that 28% of the estuaries assessed in Australia were

thought to be in a modified or severely modified condition. However, in NSW, a much higher

proportion (49%) of estuaries was assigned this status. A summary of the results of this

survey is shown in Table 1.1 below.

Table 1.1. Summary estuarine status for Australia (NLWRA, 2001)

Total PercentageStatusAustralia-wide NSW

Near pristine 49% 10%

Largely unmodified 23% 40%

Modified 17% 26%

Severely modified 11% 23%

The NLWRA has classified Myall Lakes as a wave-dominated estuary in a largely unmodified

condition. Estuaries in this condition are considered by the NLWRA as generally being in

good condition, but with some catchment and estuary impacts. This category comprised 23%

of the 979 estuaries assessed Australia wide and 40% of the 133 estuaries assessed in NSW

(NLWRA, 2001). Within NSW the majority of estuaries that were assessed fell within the

Largely unmodified category (see Table 1.1)

The Healthy Rivers Commission (HRC) Inquiry into Coastal Lakes.

In undertaking their comprehensive inquiry into coastal lakes the HRC assessed 91 coastal

lakes in NSW and classified them into categories depending on the amount of management

intervention required to ensure the sustainable health of each waterway. The 4 categories of

protection needed were:



1. Comprehensive Protection,

2. Significant Protection,

3. Healthy Modified Conditions and,

4. Targeted Repair.

Each of these categories represents the fundamental ‘management orientation’ for coastal

lakes required under the HRC’s Coastal Lake Strategy. A summary of the results of the

inquiry is shown in Table 1.2.

In undertaking their assessment the HRC based their classification on three broad factors:

? Inherent natural sensitivity to human activities (eg. from potential pollutant inflows,

flushing capacity, entrance behaviour),

? Existing condition of the catchment and lake water (eg the extent of land clearing,

potential impacts of different land uses and occurrence of water quality problems and fish

kills) and,

? Recognised natural and resource conservation values (eg presence of listed species,

ecosystem uniqueness and representativeness, commercial values, reserves).

Table 1.2. Classification of Coastal Lakes in NSW based upon the HRC findings (HRC,2002)

Management Orientation Total PercentageComprehensive Protection 18%

Significant Protection 30%Healthy Modified Conditions 39%

Targeted Repair 13%

According to the HRC findings Myall Lakes has been grouped within the Significant

Protection management framework which includes around 30% of the coastal lakes in NSW.

The HRC report recognised Myall Lakes as having an extreme natural sensitivity rating as

well as a high conservation value (HRC, 2002), and that it requires a high level of care to

ensure its future health.

Another important feature of Myall Lakes is the fact that the lakes are one of the few brackish

coastal lakes that exist in Australia and only one of the two that occur in NSW, Lake

Ainsworth being the only other. Lake Ainsworth is a small system receiving water from a

highly modified catchment and has been rated by the NLWRA as having a Modified condition



and classified by the HRC within the Targeted Repair grouping (NLWRA, 2001& HRC,

2002).

Despite their size differences, both of these lakes share similar ecological attributes, and each

has experienced periodic blue-green algal blooms in recent years. An indication perhaps of

the extreme vulnerability of this specific type of waterway and a warning in general of the

consequences of catchment degradation can have on coastal lakes.

1.4. NUTRIENT DYNAMICS IN ESTUARIES AND COASTAL LAKES.

1.4.1. The sources of nutrients.

Even pristine catchments export nutrients to coastal lakes in the waters of streams and rivers

arising within them. However, human disturbances such as deforestation, agricultural

practices (eg. fertiliser application and land clearing) or point source pollution such as

stormwater run-off can lead to a far greater amount of excessive nutrient loads being

delivered into these poorly flushed water bodies (Entry & Emmingham, 1996; Mander et al.,

1997; Jorgensen et al., 2000). For example, Eyre (1997) contrasted historical and

contemporary nutrient loads (nitrate and phosphate) into the Richmond River estuary and

found that the concentrations of nitrate and phosphate were up to 3 times greater in

comparison to when the catchment was relatively unmodified in the 1940’s. It is generally

thought that Australian waterways are particularly well adapted to function optimally when

nutrients are in very short supply (Harris, 2001) in comparison to other parts of the world

because of the aridity of the climate.

According to Harris (2001), pristine catchments generally export low loads of nitrogen (N)

and phosphorus (P), with the predominant form of N being dissolved organic nitrogen (DON),

which arises naturally from the decay of plant matter. When catchments are cleared for timber

production or agricultural use there is an abrupt change to dissolved inorganic nitrogen (DIN)

being the predominant form of N (Harris, 2001).

In such modified catchments, a change in the form and increase in the annual load of nutrients

entering waterways can lead to eutrophication, where natural ecological processes cannot

function properly (Young et al., 1996; Martin et al., 1999). Nutrient enrichment may result in

the development of algal blooms through the rapid growth of opportunistic autotrophs such as

cyanobacteria and other phytoplankton, and macroalgae (Codd, 2000; Menéndez & Comín,

2000). Also, high sediment loads can lead to an increase in the turbidity of a system, which

can alter plant assemblages, through decreasing attenuated light levels and restricting

macrophyte growth (Asaeda et al., 2001).



1.4.2. Nutrient limitation, cycling and algal production

It is well documented that nitrogen (N) and phosphorus (P) are the nutrients most likely to be

limiting primary production in aquatic and marine systems (see reviews by Young et al.,

1996; Harris, 1999). Young et al. (1996) state that in marine systems, N is the primary

limiting macronutrient, while in freshwater systems P tends to be the most likely to be the

limiting nutrient.

This occurs because in freshwater systems, rates of nitrogen fixation are relatively high,

denitrification rates are relatively low, and P is effectively bound to iron and not bioavailable.

This results in a relatively higher proportion of N to P available for algal growth. In marine

systems, nitrogen fixation rates are relatively low, denitrification rates are higher, and sulphur

binds effectively to iron in sediments, liberating P. The mechanisms underlying nutrient

limitation will also be affected by a number of factors including changes in salinity, and the

availability of other elements (Harris, 1999). Estuaries and coastal lakes experience variations

in these parameters and, accordingly, either or both of these nutrients may be limiting at

different times or under different conditions (Young et al., 1996).

In the N cycle, atmospheric N (N2) diffuses into the water column or soils where nitrifying

bacteria convert it into inorganic N in the form of ammonium (NH4+), which is available for

uptake by aquatic macrophytes, macroalgae and phytoplankton (Boulton & Brock, 1999).

Through the death and decay of organic material and by bacterial nitrification, ammonium

(NH4+ ) is converted to nitrite (NO2

-) and nitrate (NO3-), which can also be assimilated for

photosynthetic growth (Boulton & Brock, 1999). The final step in the N cycle, known as

denitrification, is the metabolic process of certain bacteria that convert NO3- back into

nitrogen gas, which is either cycled back into the system and fixed by bacteria, or is diffused

into the atmosphere (Boulton & Brock, 1999).

In impacted systems, where excessive amounts of organic carbon is present, and low oxygen

conditions occur, the process of denitrification may be interrupted. This results in the

conversion of NO3- to NH4

+ that is released into the water column for uptake by most algae

instead of being removed from the system by denitrification.

In undisturbed systems, P usually arises from the weathering of rocks and sediments, entering

the estuary as inorganic phosphate (PO43-) (van der Molen et al., 1998; Boulton & Brock,

1999). Phosphorus is rarely present in estuarine systems as dissolved PO43- because it is

rapidly assimilated by primary producers or readily adsorbs onto colloidal particles

(Gonsiorczyk et al., 1998; Boulton & Brock, 1999) but this process is greatly affected by

salinity. Unlike N, P is not readily recycled in the water column or lost to the atmosphere by



microbial degradation of organic matter, but tends to remain tightly bound to sediment

particles, mainly in conjunction with iron complexes. However, in estuarine systems when

anoxic / reducing conditions occur, sulphur forms complexes with iron which can release

PO43- into the water column. Furthermore, PO4

3- precipitates into the sediment where it may

be stored or assimilated by macrophytes via their roots (Gonsiorczyk et al., 1998; van der

Molen et al., 1998; Boulton & Brock, 1999). Phosphorus can be released from estuarine

sediments when anoxic conditions are apparent, reducing conditions exist, when the ionic

bond with iron is weakened (Boulton & Brock, 1999).

1.4.3. Response of lakes and estuaries to nutrient loads

There are a number of common and well documented symptoms of excess nutrient loading to

lakes and estuaries which include: blooms of phytoplankton and macroalgae; occurrence of

blue-green algal blooms; increased turbidity; declines in distribution or health of seagrass and

macrophytes; periodic anoxia; and fish kills. However, once these symptoms occur, the

ecosystem could already be overloaded with nutrients, and restoring the health of the system

is likely to be very difficult. According to Scheffer et al. (1993) and Scheffer (1998), this is

because shallow aquatic environments tend to exist in two stable states. Harris (1999b) further

states that estuarine systems and can switch between these two states relatively quickly. The

two states are:

1) Clear and dominated by macrophytes or seagrass, or

2) Turbid and dominated by phytoplankton.

The response of a coastal waterway to an increasing or decreasing nutrient load is complex

and non-linear especially in shallow systems. Shallow lakes are very adept at processing and

cleansing themselves of nutrient loads, but when this capacity is exceeded, the ability of the

system may ‘crash’ to a fraction of it’s previous capacity. This is due to the combined failure

of nutrient cycling processes that remove nitrogen from the sediments, and the collapse of

biological processes that maintain biodiversity and prevent the domination of a few groups of

plants or phytoplankters (Harris 1999b).

Although denitrification is the main process of nitrogen loss from most estuaries, the removal

of water column nutrients through flushing to the ocean can also play a role in lowering

nutrient loads. This can be particularly true for freshwater slugs following large rain events

that can pass right through well flushed estuaries directly into the ocean. Lakes that have long

residence times trap incoming nutrients and receive less assistance in removing nitrogen from

their waters, and consequently are naturally prone to higher N concentrations in the water



column, especially where incomplete denitrification is occurring. Complete denitrification is

further inhibited by excess organic carbon loading in these places and anoxic conditions

leading to the release of ammonia from the sediments, which fuels further algal blooms.

Under some conditions, internal cycling of nutrients stored in the sediments of coastal lakes,

particularly of N, may be the main source of nutrient loads to the water column in dry

conditions, and keeps the water column nutrients elevated during periods that would normally

be oligotrophic. The high nutrient concentrations in Myall Lakes at some times in dry weather

could be a consequence of this process. The reduction of loads from the catchment may have

little effect on the nutrient status of waterways that are nourished from benthic stores of

nutrients until a significant improvement in denitrification efficiency is achieved.

Chapter 2, Characteristics of Myall Lakes and its catchment Understanding Blue Green Algae Blooms in Myall Lakes NSW.


2. Characteristics of Myall Lakes and itscatchment

2.1. LOCATION OF STUDY AREA

Myall Lakes is a large coastal lake system on the lower north coast of NSW approximately 70

kilometres north of Newcastle.

Figure 2.1. Myall Lakes Catchment.

2.2. CHARACTERISTICS OF THE MYALL LAKES REGION

The total catchment area of Myall Lakes is approximately 780 km2 and the main input of

freshwater into the lake system is from the Myall and Crawford Rivers that join at Bulahdelah

and flow into the western portion of Bombah Broadwater (see Figure 2.1). The only other

major inflow of surface waters into the lakes is from Boolambayte Creek, which flows into

the northern portion of Boolambayte Lake. Other inputs of fresh water are from rainfall upon

the lakes’ surfaces and groundwater drainage from the sand mass on the eastern shore.

Elsewhere around the lakes the watershed lies very close to the shoreline and only limited

inputs of freshwater occur from these sources (Atkinson et al. 1981).



2.2.1. Climate

Climatic influences play an important role in affecting the characteristics of Myall Lakes with

the larger El Niño and La Niña, and seasonal climatic cycles changing the balance of

freshwater inflows, evaporation and tidal flushing within the lakes.

In dry periods, Myall Lakes increases in salinity due to evaporation and greater seawater

inflow from Port Stephens. In wetter periods, larger and more frequent rainfall events result in

larger inflows from the catchment changing the lake to a brackish or freshwater dominated

system. This increased input of freshwater often carries greater nutrient loads and sediment

derived from the catchment.

The mean annual rainfall for Bulahdelah is 1328 mm with the wetter months occurring in late

summer and early autumn with mean monthly rainfall exceeding 100 mm (see Figure 2.2).

The driest months are late winter and early spring with mean monthly rainfall about 60 mm

with summer rainfall generally more reliable than winter rainfall. Rainfall decreases inland

but upland areas probably receive more rainfall (Atkinson et al. 1981).

Mean monthly maximum temperatures range from 27 °C in summer to 17 °C in winter with

minimums of 15 °C and 3 °C respectively.

Daily rainfall records have been documented for the catchment at the Bulahdelah Post Office

since 1906. These records provide an excellent picture of long-term variation in rainfall over

the previous 95 years within the Myall Lakes catchment. Figure 2.3 below shows how the

rainfall has varied over this 95 year period.

The dashed line shows the mean rainfall of 1328 mm per year which is represented as 0 mm.

Years with lower than average rainfall move the graph down by the difference between the

average and that years total, while years with above average rainfall move the graph up by the

difference.



0

20

40

60

80

100

120

140

160

180

1 2 3 4 5 6 7 8 9 10 11 12

Month

Mea

n T

otal

Mon

thly

Rai

nfal

l (m

m)

Figure 2.2. Mean Monthly Rainfall for Bulahdelah Post Office (1906 to 2001).

-2000-1500-1000-500

0500

10001500200025003000

1906

1911

1916

1921

1926

1931

1936

1941

1946

1951

1956

1961

1966

1971

1976

1981

1986

1991

1996

2001

Year

Rai

nfal

l (m

m)

Bulahdelah Post Office

Figure 2.3. Cumulative departure from the mean for rainfall recorded at the BulahdelahPost Office.



0200400600800

10001200140016001800

1990

1991

1992

1993

1994

1995

1996

1997

1998

1999

2000

2001

Years

Rai

nfal

l (m

m)

Mean YearlyRainfallActual YearlyRainfall

Figure 2.4. Yearly rainfall recorded at Bulahdelah Post Office between 1990 and 2001.

Figure 2.3 shows that between 1906 and 1950 fairly average rainfall was experienced with

few events of greatly above average rainfall experienced. The latter part of this period

experienced a significantly dry period between 1936 and 1950. This dry period also coincided

with an increase in agricultural activities within the catchment. Between 1950 and 1980 the

Myall catchment was significantly wetter than the previous half of the twentieth century with

a number of significantly above average rainfall events occurring during this period. Between

1980 to 2001 the trend reversed and there tended to be less rainfall on average, which is

typical of an El Niño weather pattern. Figure 2.4 shows the later half of this period in more

detail. This figure illustrates the typical long term weather pattern of below average rainfall

followed by a period of sustained above average rainfall.

2.2.2. Geology and soils

The geology of the Myall Lakes catchment consists of a series of unconsolidated Quaternary

sediment deposits associated with alluvial flats and several sand dune systems with the valley

itself developing within a large syncline of varied rock types defining the catchment

boundary. The underlying bedrock of the catchment consists of sedimentary and volcanic

rocks of the Carboniferous and Permian age.

The dominant geological structure within the catchment is the Myall Syncline, which

developed after a major folding and faulting of the bedrock. The synclinal and anticlinal axes

of this system expose rock types of the Alum Mountain and Nerong Volcanics and have a

north-west and south-east orientation (Worth, 1992). Ridges flank both sides of the Myall



syncline and consist of Carboniferous rocks. These were formed between 290 – 345 million

years ago by a combination of sedimentary deposits and volcanic activity. They consist of

sandstones, mudstones and siltstones with some igneous intrusions.

The valley floor consists of Permian sandstones and shales exposed by extensive erosion

which were formed between 240 – 280 million years ago by sedimentary processes. These

formations were deposited by the ocean and have resulted in rolling hills near Bulahdelah and

Markwell and consists of sandstone, conglomerate, shale and some coal deposits.

The sediments of the Quaternary period are the most recent formations and are only 2 million

years old. These formations were deposited by alluvial processes, including weathering and

erosion, and occur in the lower reaches of the Myall River and Boolambayte Creek. Aeolian

(wind transported) and wave processes have lead to the formation of extensive dune systems

half way between Bulahdelah and the Bombah Broadwater and on the eastern side of the

Myall Lakes. These extensive sand dune deposits developed ridges that formed a barrier

system. They completely or partly enclose lagoons or swamps that form linear depressions

parallel to the shoreline.

2.2.3. Preliminary geomorphic status of the Myall River catchment.

In October 2002 the DIPNR undertook a preliminary geomorphic assessment of the Myall

River Catchment to determine the most likely location of sediment sources, stores and sinks

since European settlement.

There is little doubt that in many NSW catchments European activities such as deforestation,

and in particular the clearance of riparian vegetation has caused channel incision and bank

erosion that has lead to the degradation of the channel itself (see Brooks 1999 for example).

The Myall River is no exception to this and it has undergone a similar process to that of other

coastal streams in NSW, losing many of its pre European settlement geomorphic features.

During the field assessment two areas of sediment accumulation and four potential sediment

sources were identified within the Myall Catchment two of which are directly related to the

degradation of the Myall River. The potential sediment sources include:

Meander cutoffs on the alluvial reaches

The clearing of vegetation from floodplains and banks usually causes the geomorphic process

of channel straightening or meander cutoffs to occur with increased frequency. This is due to

the loss of bed and bank cohesion provided by riparian vegetation which in turn allows faster

bend migration, erosion of flood runners and bed lowering via ‘headcuts’.



Once bed lowering has occurred this destabilises the unvegetated banks causing them to

collapse in on themselves resulting in channel expansion. Within the area around Markwell,

bed lowering of around 1 metre is evident and is indicated by remnant bed levels of

abandoned channels and the high location of older trees that were formerly at the toe of the

bank.

Channel expansion of about 2 to 3 times is apparent, evident in the small size of recently

abandoned channels relative to the much larger size of the present channel. All of these

effects have potentially released large volumes of floodplain sand and silt into the river which

are then available to be transported downstream. These have then been either deposited on

floodplains as overbank deposition or flushed through the system and into the Lakes.

Bed incision on partly confined reaches

Upstream of Markwell the bed of the Myall River has incised about 0.5 m, which may be the

result of the removal of logs from within the stream and by increased runoff from the cleared

catchments. This process is indicated by the exposure of large cobbles in the bed. According

to Nanson and Doyle (1999), these streams would have had sandy or gravelly beds and large

loadings of wood before European settlement.

Cobble beds with very little wood are now a common feature of the Myall Catchment with

most of the sand and gravel already being washed out of the upper reaches of the catchment.

However these reaches will still be contributing small amounts of coarse sediment.

Gullies

A few eroding gullies were evident in the upper catchment and would be contributing a small

amount of coarse sediment to the lower order tributaries of the Myall River. This observation

agrees favourably with that of Atkinson et al. (1981) who noted that no appreciable

accelerated erosion was evident throughout the Myall Lakes catchment although some

localised gully erosion was evident.

Slopes direct to streams

A few eroding slopes were evident within the Boolambayte Creek catchment. Sites such as

these would be contributing a small amount of fine sediment to the lower order streams.

Sediment Stores



The floodplains adjacent to the Myall River are functioning as sediment stores (areas where

material may be accumulated temporarily). This material would be mobilised during flow

events that flow over the floodplain. Floodplain stripping or reworking is common on these

types of rivers given the nature of flows, and high flow events may be sufficient to scour

around vegetation or to strip the top layer of floodplain surface. Flood channels are also

features within the floodplain itself, which during smaller flow events may release stored

material through the loss of vegetation and subsequent bed lowering.

Sediment sinks

Sediment sinks are the places where sediment is permanently removed from the system so

that it does not move further down the river, at least in the historical time scale. The main

catchment sediment sinks observed within the Myall catchment are the terraces in the wider

parts of the alluvial valley. These are very old deposits and are not a part of the present

sediment budget and have formed via the deposition of sediment at the edges of the valley on

the old floodplain during the Holocene period upstream of Bulahdelah (Thom, 1965). During

this period south-eastern Australia was wetter and therefore more fluvially active resulting

higher stream flows and the formation of the features (Nanson and Doyle, 1999).

Therefore from preliminary investigations, the major sources of sediment in the Myall

catchment appear to be streambeds and stream banks with a small input from cleared gullies,

with slope erosion contributing a minor amount. This is consistent with other findings for east

coast catchments (Brierley and Fryirs, 1998, Caitcheon et al., 2001). The main sources of the

stream bed and bank sediment appear to be derived from channel incision and expansion on

the alluvial reaches, which has occurred around the middle of the catchment. This too is

consistent with other east coast catchments in that the middle reaches of east coast rivers

appear to be the most impacted by anthropogenic activities. According to Nanson and Doyle

(1999), the flood events that occurred in the late 1940’s and early 1950’s were widely

reported as channel modifying events within coastal NSW. This correlates well with Figure

2.3 which shows above average rainfall within the Myall catchment coinciding with the

increased landuse within this timeframe.

The preliminary results of this qualitative study indicate that the Myall River has contributed

and potentially continues to contribute a significant quantity of material downstream during

high flow events. This conclusion is contrary to the findings of Worth (1992) and further

quantitative investigations are required.



2.2.4. Settlement History and Landuse.

European settlement in the Manning and Karuah catchments, which included the Myall

Catchment, occurred between 1804-1817 (DLWC, 2000). Prior to this the Myall catchment

was inhabited by the Worimi aboriginal people whose area extended from Port Stephens in

the south to Forster/Tuncurry in the north and as far west as Gloucester. The early European

development of the region was directly linked to the timber resources of the area, with cedar

felling preceding both agricultural and urban development.

By 1817 cedar was being transported to Port Stephens and shipped to the settlements at

Newcastle and Sydney. Timber grants were given out in the early 1830s and by the late 1830s

cedar cutters had worked their way up the coast, reaching Coolongolook. Sawmills were

established on the foreshores of the Myall Lakes and Boolambayte Creek. Most of the timber

cut in the district was used for ship construction, with the timber being hauled down the Myall

River.

In about 1825 the Australian Agricultural Company was formed and given a land grant of 404

858 hectares extending from Port Stephens to the Manning River. However the company

found that the land was largely unsuitable and a land swap was made with the Crown. The

township of Bulahdelah was established in 1857 at the junction of the Myall and Crawford

Rivers.

Initial attempts at dairying failed, due to the soil limitations and restricted transport network.

Beef cattle production therefore became the predominant farm landuse. Timber production

expanded rapidly during World War II to provide essential materials for the war effort. The

area developed into a major forestry district, however its full potential was not exploited due

to transport network limitations.

Grazing in the area was initially based on native pastures however, the introduction of the

mechanised farm machinery in the 1940’s allowed improved pasture to be sown. By 1948

virtually every property along the Myall River was a dairy farm. These were mostly small

family farms, stocking an average of 30 cows each. Corn was also grown extensively along

the river flats to provide feed for cattle during the winter.

The current landuses in the catchment still include pasture production associated with the

grazing of beef and dairy cattle, although only 5 dairies are still in operation. The major

landuse within the catchment is timber production/conservation, and recreation and tourism

with a large section of the catchment to the east, west and south covered by State Forests and

National Park (see Table 2.1).



State Forests cover an area of 26 414 hectares. These forests include Nerong State Forest (8,

200 ha) which is situated on the western side of the Pacific Highway south of Bulahdelah and

the Myall River State Forest (19, 100 ha) is a large area of forest that extends along the

western boundary of the Myall catchment and Bulahdelah State Forest, which is located in the

middle, east and north-eastern parts of the catchment.

The Myall Lakes National Park was established in 1978 covers an area of 44 612 hectares,

and is the only national park in NSW that comprises an entire waterbody and shoreline. As

well as the conservation of native plant and animals, the national park supports a range of

tourist and recreational activities including, camping, bushwalking, picnicking, swimming,

boating and fishing.

Table 2.1. Landuses of the Myall Catchment.

Landuse Percentage of catchment areaState Forest 32.5

Privately held forest lands 20.2National Park (native vegetation) 19.4

Poultry Less than 1%Grazing -Native Pasture 13.1

Grazing -Improved Pasture 1.3

Dairy UnknownUrban 0.2

Rural Residential 0.3Other 0.3

Roads and Easements 0.2Water (Rivers and Lake area) 12.5

2.2.5. Human settlement.

There are two main population centres within the catchment, these are Bulahdelah, through

which the Pacific Highway runs, and Hawks Nest / Tea Gardens. The population of these

centres is 1161 and 2545 respectively (G. Tuckerman pers. comm). Hawks Nest and Tea

Gardens are popular tourist destinations and provide access to the Myall Lakes National Park

and eastern shore of the Bombah Broadwater.

Bulahdelah is the largest centre upstream of the lakes and the commercial centre of the upper

catchment with the remainder of the catchment dominated by rural holdings. The name

Bulahdelah comes from the Worimi people’s original name for the area and means “the place

beneath a mountain where two rivers meet” these two rivers being the Myall and Crawford

Rivers.



Downstream from Bulahdelah Mid-Coast Water operates a Sewage Treatment Plant (STP) for

the township. The STP discharges treated effluent to Frys Creek, a tributary of the Myall

River and was upgraded to tertiary level treatment in 1996 to meet the NSW Environment

Protection Authority discharge standards for protected waters. Prior to this effluent was

discharged following secondary treatment only.

2.3. CHARACTERISTICS OF THE MYALL LAKES SYSTEM.

2.3.1. Geography

The Myall Lakes system lies within 2.5 kilometres of the Tasman Sea and is separated by two

distinct dune systems with a minimum topographic relief between the lakes and the ocean of

20m (Skilbeck et al. 1999). The system is made up of a series of four interconnected brackish

lakes: Myall Lake; Boolambayte Lake; Two Mile Lake; and Bombah Broadwater which give

Myall Lakes a total water surface area in excess of 100km2. The lakes are drained to the ocean

by the lower Myall River, which stretches 26km from Bombah Broadwater to Port Stephens.

Myall Lakes overlies the New England Fold Belt, which has largely determined the

configuration of the lakes. The western shoreline and the islands within the system are

comprised of bedrock outcrops comprised of irregular Carboniferous sediments of the New

England Fold Belt. The eastern shoreline has mainly been formed by the two distinct dune

systems of the late Pleistocene and Holocene, which link headlands formed from

Carboniferous outcrops (Skilbeck et al. in press). The lakebed is formed between the wide

Pleistocene ridge and the Holocene beach systems. This represents the most recent marine

transgression and may have reached a standstill about 5000 years ago (Worth, 1992).

Lakeshore features such as the sand and pebble dominated beaches and bluffs that occur along

the shoreline of Myall Lake in the north have been described by Thom, (1965) as relic

features representative of a period of higher energy within the lake. As no marine fauna or

extensive aeolian deposits have been found along the shorelines, Thom (1965) concluded that

both the cliffs and beaches are relic lakeshore features possibly a result of a period of

increased wave energy. The relic shorelines therefore suggest a decrease in the intensity of

wave action accompanying the siltation of the lake.

2.3.2. Lake flushing.

Unlike most open lake systems in NSW that are close to the ocean much of Myall Lakes is

not subject to semi-diurnal tidal flushing, saline water only moves up the system in extended

periods of low rainfall. The lower Myall River and southern portion of Bombah Broadwater

appear to be the only parts of the lake system that are subject to significant tidal flushing



(Atkinson et al. 1981). Therefore the amount of water able to leave the lakes each day is small

compared to the volume of the lakes. This means that due to the limited exchange with the

ocean any nutrients that enter the lake system, especially during large rain events, are likely to

be retained within the lakes.

Sampling for total salts by Atkinson et al. (1981) in the lakes between 1972 and 1978 showed

inter-lake variability in salinity with the upper portions of the lakes exhibiting a low range in

salinity while Bombah Broadwater exhibited the widest range of salinity (Ryan, 2002). Manly

Hydraulics Lab (MHL, 1998) reported that salt water entering the lakes via the lower Myall

River is trapped in Bombah Broadwater and then slowly flows up the rest of the system as a

gravity current. Wind and convection currents cause vertical mixing of lake waters.

The constriction of the lakes’ entrance has resulted in long water residence times within the

lakes system. These times have been calculated by Manly Hydraulics Lab (1999) at between

400 to 800 days which is much longer than most other NSW coastal lakes. This figure was

derived from salinity data and is an estimate of the approximate time for the whole volume of

the Myall Lakes to exchange with Port Stephens. This long flushing time also gives the lakes

a large salinity range as discussed further in Chapter 5, with the southern part of Bombah

Broadwater exhibiting estuarine characteristics and Myall Lakes freshwater characteristics.

The long water residence and flushing times are also important because it means that that the

lakes are very sensitive to human activities in the catchment and essentially act as a ‘sink’ for

nutrients. Atkinson, et al. (1981) identified this and stated that the lack of flushing of the

system upstream of Bombah Broadwater makes this area particularly susceptible to pollution

and eutrophication.

2.3.3. Lake Structure and Bathometry

In 2001 DIPNR carried out a bathometric survey of Myall Lakes as part of the NSW

Government’s Estuary Management Program (Figure 2.5). The aim of the bathometric survey

was to provide not only an accurate picture of navigable waters within the lakes system but it

will also provide catchment managers with an accurate base upon which changes in aquatic

vegetation could be mapped and areas of significant sediment inputs from the catchment

identified.

From the data collected in the survey the average depth of Myall Lakes has been calculated at

2.7m, which is shallow in comparison to other coastal lakes. Nevertheless, the bathometry of

Myall Lakes is quite varied with some areas ranging in depth quite significantly. Boolambayte

Lake for example has a maximum depth of 13 metres at Violet Hill but has an average depth

of 2.3m.



Figure 2.5 Bathometry of Myall Lakes.



The mouth of the Myall River is another area of deep water with its deepest part 6.5m deep

although the bed level quickly shallows up 1.5 upon entering Bombah Broadwater. The

Broadwater itself is also quite interesting with large areas of shallow water on the northern

and eastern shores. These areas are sandy and flat topped and range in depth from 1 to 1.5m

on average but then quickly drop off into deeper water, which occupies the remainder of the

Broadwater. These two areas are well developed and occupy quite a significant area of the

northern and eastern shorelines of the Broadwater.

Two-Mile Lake is also dominated by a large sand bar feature on its south-western shoreline.

This feature like the ones in Bombah Broadwater rises very quickly to an average depth of

between 1 to 1.5m from about 4m in the main channel.

Smaller sand bar features also occur on the eastern shore Myall Lake in Palmers Bay and

Kataway Bay but these are not as dominant as the ones in Bombah Broadwater and Two Mile

Lake. The bar features described exhibit similar depth characteristics and rise rapidly from the

lakebed to a depth of 1 to 1.5m from and average of about 2.5 to 3m. The remainder of the

lakebed, generally below 2m is comprised of muds. Thom (1965) reported that preliminary

observations reveal that the lake bottom is comprised of soft muds and fine organic debris.

Along the western shoreline of the lakes the shallow bays are typically dominated by a muddy

substrate but this is in some cases overlayed by matter high in organic content, which will be

discussed further in Chapter 6.

Work is still ongoing with the development of a hydraulic model for the Myall Lakes system.

This will enable prediction of lake circulation patterns that are present and what affect these

movements have on the mixing of waters and the movement of algae and nutrients within the

water column.

2.3.4. Sedimentology of the Broadwater, Myall Lakes, NSW.

Worth (1992) undertook a study as part of a Graduate Diploma at the University of Newcastle

to describe the sediments of the Bombah Broadwater and investigate their possible origin and

rate of accretion. A number of possible sources of lacustrine sediment were envisaged from

the geological formations and the landuse history within the catchment. These included;

suspended material transported from the Myall River, deposited organic material and beach

sands from the Holocene and Pleistocene dune systems.



An estimation of the accretion rate of sediments was obtained using two different methods

that utilise the decay or radioactive isotopes. These were radiocarbon dating (C14) and

radioactive caesium dating (Cs137). The average accretion rate of sediment in the Broadwater

was estimated to be 0.10 cm/yr over the last 1190 years (using the radiocarbon dating) and

0.184 cm/yr over the last 38 years (for the Cs137 dating) (Worth 1992). Worth (1992) states

that the agreement between these two rates many indicate a long term stability in the system

which is supported by other evidence from the upper Myall River, although this evidence is

not discussed. Also, radiocarbon dating was only carried out on one core only at the mouth of

the Myall River whereas the radio Cs137 dating carried out on 12 cores.

According to Worth (1992), the benthic sediments of the lake and associated waterways

appear to consist mainly of silt and clay precipitated under increasing salinity as the waters

move downstream. The actual site of this precipitation may vary according to the flooding by

the river (Worth 1992). Worth concluded that since European settlement, anthropogenic

disruption to the natural regimes of erosion and sedimentation in the catchment have been

minimal, which is in conflict with the findings of Section 2.2.3, which found significant

erosion in some subcatchments had occurred. Obviously, further investigation of sediment

accretion rates within the lake (including the influences of factors such as bioturbation and

resuspension by wind) is required before an accurate picture can be acquired.

2.3.5. Benthic Nutrient Fluxes in Bombah Broadwater, Myall Lakes.

In June 2000 the Australian Geological Survey Organisation (AGSO, now Geosciences

Australia) conducted an eleven-day study in Bombah Broadwater, measuring fluxes of

nutrients from sediments of different types using benthic chambers. The aim of the study was

to provide an estimate of the fluxes of different forms of nitrogen from the sediment into the

water column. Three sites were established two on mud substratum and a third on shallow

sandy material near Mungo Brush.

It is important to note that the benthic chamber study was undertaken on a single occasion

during winter months and it is possible that the nutrient fluxes might not be typical of the

rates at other times of the year. The estimates of sediment denitrification in Myall Lakes

indicates that denitrification efficiency was low (approximately 40%) during the study at the

mud sites. The sandy location in the eastern Broadwater however, had a fairly high

denitrification efficiency (approximately 80 %, see Figure 2.6). The results suggests that at

the time of the study Bombah Broadwater was in a state in which labile nitrogen in the form

of ammonia from the sediments was contributing to plant growth. It is possible that the



extended cyanobacterial bloom experienced in Myall Lakes over the summer of 1999/2000

was exacerbated by poor sediment denitrification (AGSO, 2000).

In summary, the results from the AGSO study indicates that at the time of the study:

? within the mud substrate, Myall Lakes exhibited high organic carbon loads and low

denitrification efficiencies;

? within the sandy substrate areas Myall Lakes exhibited low organic carbon loads and high

denitrification efficiencies;

? the denitrification efficiencies in the mud facies are low when compared to other similar

Australian estuaries; and

? the contrasting poor mud denitrification and good sand denitrification may, in part,

balance the overall efficiency of the Broadwater’s denitrification.

It is difficult to generalise about the system-wide denitrification rate from the limited data

available, particularly in light of the findings of the sediment survey (Chapter 6). However,

the denitrification efficiency of the mud substrate is probably more representative of the

system as a whole than the sand facies. However, the low efficiency in muddy places may be

ameliorated to some extent by the high denitrification efficiencies within the sandy substrate

areas. The low denitrification efficiency at the mud sites is verging on values that the AGSO

PPB model of estuarine eutrophication predicts as being within the range typical of a

eutrophied waterway (Figure 2.6).



Figure 2.6 The modelled relationship between residence time of nitrogen in an estuaryand sediment denitrification (AGSO, 2000). Residence time is defined as the number oftimes added nitrogen is recycled between sediments and the overlying water column. (NB.Port Phillip Bay is also an area where elevated nutrients are causing detrimental changes to itsecology).

2.3.6. Groundwater quality.

Groundwater within the Myall Lakes Catchment occurs in both fractured rock aquifers and

unconsolidated sand deposits. Deep groundwater is generally associated with the fractured

rock formations of Carboniferous and Permian origin. These groundwaters contain higher salt

concentrations due to their contact with rock formations that originated in a marine

environment. The regional groundwater flow in these fractured rock aquifers is from the

north-west to south-east.

Unconfined perched aquifers occur almost everywhere in the Quaternary sands in the Myall

Lakes National Park. These unconsolidated sand deposits generally have a high degree of

porosity and permeability. These properties provide the sands with high storage and

transmitting abilities. The local groundwater flow in the sand dunes east of Myall Lakes is

either north-west to south-east towards the lake or north-east to south-west towards the ocean

depending on the lake and sea level fluctuations (DLWC, 2000b).

Information describing groundwater around the Myall Lakes National Park (and hence land

immediately adjacent to the lake system) was mostly derived from the results of the

groundwater study carried out by DIPNR for NPWS from 1999 to 2002 (DLWC 2000b). The

objective of the study was to describe the character of the groundwater and determine the



extent of septic effluent impacts (if any) on the groundwater systems of Myall Lakes. The

groundwater study involved a field investigation and the establishment of a groundwater

monitoring network and quarterly sampling for a period of three years to benchmark the

undisturbed condition of groundwaters and monitor changes in the groundwater quality that

may result from the septic effluent dispersal into the sub-surface. Thus, a number of bores in

Control and Impacted (near known sources of effluent containment and disposal) locations

were established and monitored over the period.

The groundwater monitoring included field measurements of the groundwater level, EC, pH

and water temperature and collection of samples for laboratory analysis. For each bore, the

first sample was analysed for major ions, trace elements, alkalinity, EC, pH, total nitrogen,

ammonia, nitrate, nitrite, total phosphorus, total reactive phosphorus, faecal coliform and

faecal streptococci. Subsequent quarterly samples were analysed for EC, pH, total nitrogen,

ammonia, nitrate, nitrite, total phosphorus, total reactive phosphorus, faecal coliform and

faecal streptococci.

The various aquifers that exist in the Myall Lakes National Park based on geology from oldest

to youngest are:

? Permian sedimentary rocks;

? Carboniferous sedimentary and volcanic rocks;

? Quaternary sediments consisting of,

? Pleistocene Inner Barrier Sand Dunes to the west of the lakes; and

? Holocene Outer Barrier Sand Dunes to the east of the lakes (ocean side).

The Permian and Carboniferous aquifers are further subdivided into various formations based

on their origin and location. However, these subdivisions were not described here in detail as

the groundwater study concentrated mainly on the Quaternary sediments where most of the

campsites and septic toilets were established. The Quaternary sediments are further

subdivided according to age and location as this has significance on the occurrence of acid

sulphate soils mainly associated with the Inner Barrier Sand in estuarine flood plains.

The type of groundwater is a reflection of the geology of the aquifer, the source or origin of

the groundwater plus the physical, chemical and biochemical processes taking place in the



sub-surface. The groundwater in Myall Lakes National Park has been characterised based on

electrical conductivity, pH and dominant major ions.

2.3.6.1. Groundwater Electrical Conductivity

Fresh, brackish and saline groundwaters are found in the Myall Lakes area. The major

component of fresh groundwater is rain that is naturally low in salinity. The salinity of this

type of groundwater in Myall Lakes National Park ranges from 30 to 300 ?S/cm with a

median of 100 to 150 ?S/cm. Fresh groundwater can be found in the Outer Barrier sand dune

systems especially at Mungo Brush, Bombah Broadwater, Bombah Point, Myall Shores, near

the wetlands south of Boolambayte Lake, along the Old Gibber Road and along the track to

the Myall River Mouth.

The second type of groundwater is brackish groundwater, which is a mixture of fresh

groundwater and some recently intruded seawater. The conductivity of this type of water

ranges from 100 to 2300 ? S/cm and it has a median conductivity of 300 to 350 ?S/cm. The

salinity of this type of water is highly variable due to the influence of rainfall, the lake, and

sea level fluctuations. More saline groundwater occurs during dry periods when there is very

limited dilution from local rain. On the eastern side of the Outer Barrier sand dunes, seawater

exists as a wedge beneath the fresh groundwater with its thickest part towards the ocean.

Brackish groundwater occurs where these two systems mix. It is drawn closer to the surface

by pumping of the spear points supplying water around the campsites at Mungo Brush and the

NPWS depot. On the western side of the Outer Barrier sand dunes, the brackish groundwater

is hydraulically connected to the lakes. Brackish groundwater is present in the sand dunes in

Mungo Brush, White Tree Bay, Mungo Point, Bombah Point and Yagon.

The third type is saline groundwater originating from the Carboniferous and Permian

sedimentary rocks located to the west of the lakes. The maximum salinity of this type of water

is generally higher than the brackish groundwater found in Quaternary sands. The salinity

levels of Carboniferous and Permian groundwaters varies less during dry periods. This could

indicate a slower response to rainfall recharge, which only occurs in regional groundwater

systems.

All three types of groundwater are hydraulically connected with the lakes. Faults and fractures

in the Permian aquifers may also result in groundwater seepages especially in the Inner

Barrier sand dunes to the west of the lake. Groundwater from the sand dunes discharges into

the lake when lake water levels are low, and recharge when lake levels are high.



2.3.6.2. Groundwater pH

The pH of the groundwater in the Myall Lakes area is a function of any, or a combination of,

the following:

? the presence and amount of organic substances (eg Humic and tannic acids); and

? the chemical weathering of minerals (especially pyrite and arsenopyrite in acid sulphate

soils).

Based on pH, groundwater in Myall Lakes can be grouped into two categories. The first group

is classified as slightly acid groundwater with a pH ranging from 4.5 to 7.5 and median of 6.0.

This range of pH was encountered in monitoring bores in Mungo Brush, White Tree Bay,

Myall Shores, Korsmans Landing, Yagon, Mungo Point and Bombah Point.

The second group is classified as highly acidic groundwater with pH ranging from 3.5 to 5.0

and median of 4.0 to 4.5. This was encountered in Bombah Broadwater, near the pond at

Bombah Point, near the wetlands south of Boolambayte Lake, along the Old Gibber Road and

along the track to upper Myall River Mouth.

Both types of groundwater have a distinct odour and brown colour resembling humic acid.

This indicates the high organic content of the sands that could be due to the breakdown of the

abundant plant materials in the sediments. There was no correlation found between salinity

and pH in any of the groundwater samples.

2.3.6.3. Groundwater Chemical composition.

From the results of the groundwater monitoring project, classification of the types or classes

of groundwater in Myall Lakes National Park based on the most dominant major cations and

major anions can be developed. Results from these classifications are listed in Table 2.2.

Table 2.2. Classes of groundwater in Myall Lakes National Park identified bygroundwater monitoring bore areas.

Type Locations of similar Groundwater type. Chemical elementor compound

1 Mungo Brush, Broadwater, Bombah Pt, KorsmansLanding, Mungo Point, Bombah Point, The Big GibberQuarry, Myall Lake area

Na - Cl

2 Myall Shores, Old Gibber Rd, River Mouth Na – Mg - Cl3 White Tree Bay Na – Mg – Cl - HCO3

4 Yagon Na – Cl - HCO3

5 Mungo Brush Na – Mg - HCO3 - Cl6 Myall Shores Resort Na – Ca - Mg - HCO3 - Cl



Further classification of groundwater type was undertaken using Piper diagrams which

assisted in classifying the groundwater according to the dominant major cation and major

anion pair (consisting of Na, Mg, Ca, Cl, SO4 and HCO3). By plotting the groundwater

samples results in comparison with known compositions of other water sources (eg. seawater,

rainfall, lake water and wetland water) the dominant sources of groundwater in different

locations were identified.

Based on the Piper diagram assessment it was concluded rain and seawater are the two main

components of the groundwater of Myall Lakes. The majority of the groundwater samples

analysed were similar in type to seawater (showing a dominance of the Na - Cl ion pair).

Exceptions were found however for the samples from Myall Shores which reflected ionic

composition similar to that of rainwater. Groundwater composition in this area was found to

have Na, Mg - HCO3 ion pair as its dominant component.

2.3.6.4. Indicators of Possible sewage contamination.

The groundwater quality parameters used in the groundwater monitoring included faecal

coliform, faecal streptococci, total nitrogen, ammonia, oxidised NO2 and NO3, total reactive

phosphorus and total phosphorus. These parameters were used as surrogate parameters to

identify sewage effluent impacts on the groundwater.

2.3.6.4.1. Faecal Bacterial.

During the first year of groundwater monitoring faecal bacteria either in the form of faecal

coliform or streptococci, were either 1 Colony Forming Unit (CFU)/100 mL or below the

detection limit. Analysis for faecal bacteria was dropped from subsequent samples and the

monitoring was focused on the nutrient concentrations. The absence of faecal bacteria in the

groundwater could be due to the very low pH and the highly variable salinities of the

groundwater resulting into a very unstable environment not suitable for bacterial survival and

growth. Reduced or oxygen depleted groundwater systems may also inhibit bacterial survival.

2.3.6.4.2 Nutrients.

In general, the groundwater in Myall Lakes National Park has naturally high nutrient

concentrations. These concentrations are similar to those found in the surface waters of the

Myall Lake system, based on the results of the surface water monitoring (Chapter 5). The

control or reference nutrient concentrations in the groundwater from unimpacted locations are

presented in Table 2.3 below:



Table 2.3. Nutrient concentrations in control bores in Quaternary sands of Myall LakesNational Park.

Analyte Minimum(mg/L)

Maximum

(mg/L)

Average

(mg/L )

Median

(mg/L)

Total P 0.013 0.192 0.061 0.052

Soluble Reactive P 0.008 0.148 0.050 0.046

Total Nitrogen 0.200 2.100 0.878 0.930

N as Ammonia 0.020 0.270 0.154 0.165

NOx 0.010 0.160 0.040 0.020

Over the monitoring period, the median control total P and soluble reactive P concentrations

were exceeded only once at impacted bores - Bombah Point in January 2001.

The median control total nitrogen concentration was exceeded several times at impacted bores

at Myall Shores near the evapotranspiration trench in November 2000, January 2001, January

and May 2002. The concentration of ammonia (as N) was consistently higher than the control

in White Tree Bay during the entire groundwater monitoring period and was exceeded several

times at Mungo Brush and Myall Shores from October 1999 to March 2000 and November

2000 up to May 2002 (Figure 2.7). Korsmans Landing showed higher concentrations of

ammonia (as N) than the control only in January 2000. While no direct observation of

contamination of groundwater by waste-water was made, there is little doubt that the elevated

nutrient concentrations near the Myall Shores ‘Ecotourism’ resort are due to contamination,

which has been contributing to nutrients in the groundwater and probably Myall Lakes. These

loads have been partially quantified in Chapter 3, to estimate the maximum possible load

arising from visitor waste activities.

The median control oxidised nitrogen (NOx) concentration was exceeded by samples from

Bombah Point in January 2001 and Myall Shores in October 2001 and May 2002. The

concentration at the remainder of groundwater monitoring sites was consistently lower than

control or below laboratory detection limits. These data are discussed in more detail in the

groundwater study report (DWLC 2000b).



Ammonia concentration at Control (C) and Impacted (I) bores.

0

0.5

1

1.5

2

2.5

3

Aug

-99

Oct

-99

Jan-

00

Mar

-00

May

-00

Jul-

00

Nov

-00

Jan-

01

Apr

-01

Date

Am

mon

ia (

mg/

L) Myall Shores (I)

Myall Shores (I)White Tree Bay (I)

Mungo Pt (C)

Myall Rivermouth (C)

Figure 2.7. Groundwater ammonia concentration in Control and Impacted bores.

August 1999 to April 2001.

2.3.6.4.3 Nutrients Trends versus Water Level Trends

Most of the groundwater monitoring sites shows nitrogen trends similar to the watertable

trends, ie. when water levels fall, the nutrient levels also fall. This means that the

groundwater level fluctuation has a direct effect on the nitrogen distribution. The exceptions

were Mungo Brush (GW078018), Bombah Broadwater (GW078020) and Myall Shores

(GW078022 and GW078023). In Bombah Broadwater, there was an increase in ammonia

levels in 2001 despite the groundwater level falling. In Myall Shores and Korsmans Landing,

both total N and ammonia levels increased as groundwater levels fell.

All of the monitoring sites show total phosphorus trends opposite to the watertable trends.

Reactive P trends are highly variable both in the control and other monitoring bores. Mungo

Brush (GW078018), Bombah Broadwater (GW078020) and Bombah Pt. (GW078021) show

continuously falling reactive P trend. At White Tree Bay (GW078019), reactive P trend is

almost similar with the groundwater trend. Myall Shores (GW078022 and GW078023)

shows almost flat linear slightly increasing trend indicating stable reactive P distribution with

no effect from watertable fluctuation. At Korsmans Landing (GW078024) reactive P trend

show continuous increase while the watertable fell.

2.3.6.4.4 Nutrients and Park Occupancy

The number of people visiting and camping at Myall Lakes National Park peaks during

Christmas, Easter, and school holidays in July and the October long weekend. The number of



visitors to the popular campsites and Myall Shores Resort during the 1999 peak periods were

recorded (Table 2.4).

Table 2.4 Estimate of park occupancy rate (Environmental Management Pty Ltd, 2000)

Peak Season Duration (days) 1999 Park Total Occupants(Actual)1

Christmas 12 - 22 490

Easter 6 - 15 614

July School Break 15 300

October Long

Weekend

3 - 14 380

1 Data from Barry McKibbin (Myall Shores Resort Manager, pers. comm. 2001)

Nutrient levels were compared to the total number of visitors for each peak period in 1999.

The same 1999 values for park visitors were assumed and used for 2000, 2001 and 2002 due

to lack of data.

In general, nutrient level fluctuations do not show a correlation to the park’s occupancy rate

except for nitrogen levels (both total N and ammonia) in Myall Shores (GW078022 and

GW078023) (see Figure 2.7).

2.3.6.4.5 Synopsis

Despite the naturally high background nutrient levels in the groundwater, there are sampling

sites that show elevated nutrient levels that appear to be linked to effluent contamination. In

most cases, the distribution of nutrients in the groundwater indicates the influence mainly of

watertable fluctuation, which is the result of climate or rainfall. Human activities including

septic sewage disposal may have some influence on the groundwater nutrient levels and

distribution at some bores (mainly those located at Myall shores).

It is considered that when the groundwater is low (deeper) and nutrient levels are high,

nutrients are not necessarily ending up, or contributing greatly, to the lake’s total nutrient

load. The similarities in the water qualities of the lake and the groundwater plus the type of

geology of the aquifers and the lake suggest the direct hydraulic connection between these

two reservoirs. With the constant exchange in water, the groundwater and the lake are also

exchanging nutrients continuously. Groundwater recharge, in the Quaternary sand after a rain

event, is believed to be instantaneous. Therefore, significant nutrient transfer from the

groundwater can only occur when there is significant recharge resulting in higher (shallow)

groundwater levels and a hydraulic gradient towards the lake.



The movement and volume of nutrients from impacted locations to other water bodies (ie.

swamps and lakes) was not studied. However, it is assumed that part of the nutrients will be

consumed by vegetation, released back into the atmosphere, changed to stable forms, and

some portion will remain for transfer to wetlands and /or the lakes. In the case of potential

direct contamination from Myall Shores, there is a shorter pathway for the groundwater

nutrients to the lake.

As demonstrated in this study, groundwater in the Myall Lakes National Park is considered

highly vulnerable. Its strong linkage with the surrounding swamps and lakes can provide a

pathway for nutrients to reach the lake, which in significant quantities, contribute to the total

nutrient load entering the lake. In Chapter 3, nutrient loads from human activities on the lake

foreshore (which usually enter the lake via groundwater) are derived and compared to loads

from other sources.

Chapter 3, Nutrient sources to Myall Lakes. Understanding Blue Green Algae Blooms in Myall Lakes NSW.

NSW Department of Infrastructure, Planning, and Natural Resources35

3. Nutrient sources to Myall Lakes.

3.1. CATCHMENT NUTRIENT INPUTS TO MYALL LAKES.

The eutrophication of Australian waterways through the addition of excessive nutrient loads

arising in their catchments has led to an increase in the severity and frequency of algal blooms

(Young et al. 1996).

A number of complex processes are involved in the movement of nutrients from the landscape

into waterways. These include transport and redistribution processes changes in elemental

speciation and microbial nutrient cycling. For the development of management strategies the

establishment of estimates of annual nutrient loads provides a good first measure of

catchment condition. The modelled estimation of annual nutrient loads using generation rates

for differing land, attempts to isolate some of the release processes such as erosion,

atmospheric contribution, fertiliser and decay of organic matter. Despite its limitations

nutrient load modelling provides a means of identifying principal source areas, which is

important information for planning nutrient reduction strategies (Young et al. 1996).

3.1.1. Catchment Management Support System Modelling.

The CMSS (Catchment Management Support System) model was developed by the CSIRO

Division Of Water Resources to provide a tool to assist in the understanding of nutrient

generation on a catchment scale. The CMSS model utilises data relating to mapped land

attributes; estimation of nutrient generation rates (derived from published scientific literature

and research), land management information, and rates of instream process. The CMSS model

has been developed to consider catchment-scale issues and hence provides a method that can

be used to compare the relative significance of contributions from nutrient sources in a

catchment (Farley and Davies 1993).

The CMSS model for the Myall Lakes catchment was developed from field-verified landuse

mapping information (1997 aerial photography). In the development of the model reference

was made to geology, land capability information, and soil landscape mapping information

held by DIPNR. Nutrient generation rates for various landuse activities were developed from

published Australian information and considered in context of the mapped landuses.

In the Myall Catchment a number of point-source nutrient loads were identified. These

included dairy shed effluent, poultry sheds, and the Bulahdelah STP. The treatment plant

removes nearly all phosphorus from effluent, with the nitrogen component remaining.



Table 3.1. Land use nutrient generation rates used for Myall Catchment CMSS model.

Land Use Phosphorus kg/ha/yr Nitrogen kg/ha/yr

Urban 1.30 9.0Improved (Dairy) Pasture * 1.5 6.0

Roads 1.80 6.0

Rural residential 0.60 4.0Timbered Land (not NP, not SF) 0.20 2.0

Native Pasture * 0.15 2.0National Park (NP) 0.08 1.5

State Forest (SF) 0.12 1.5

Easements 0.15 1.5Dairy cow unit (500 kg)# 0.0047 0.0225** Poultry manure per 120 m X 12mshed

0.5 Tonnes / yr 1.75 Tonnes / yr

(Note: These rates indicate potential contribution developed from Hunter Catchment CMSS Model Hancock 1997)

Reference * Bagsinka et al. (1998) # 10% of actual manure produced.** Poultry manure : 5 batchesyear, full clean out, 105 m 3 manure produced per batch, 75 % (DM) dry matter ; Nitrogen 2.6% DM - 30% readily available ; Phosphorus 1.8 % DM 13 % readily available. Assume available N and Ptransported and lost in run-off.

3.1.1.1. Comparison of loads arising in Myall Lakes sub-catchments.

The Myall Lakes catchment can be divided into 4 sub-catchment areas. Of these the Myall

River catchment has the largest land area. The areas of each sub-catchment are shown below

(Table 3.2).

Table 3.2. Description of sub-catchments of Myall Lakes catchment.

Sub-catchment Land Area Ha Percentage ofCatchment Area

Myall River Catchment 44 362 54.5Nerong Area Catchment 3 938 4.8Boolambayte Creek Catchment 9484 11.7Myall Lakes and Lake's edge Catchment 23584 29.0

The CMSS model can be used to develop a comparison between the sub-catchment areas to

compare estimate of nutrient delivery. The results in Table 3.3, and Table 3.4 summarise the

modelled nutrient load arising in the 4 main subcatchments of the Myall Lakes system. It is

clear from these tables that approximately 70% of the total annual load of N and 80% of the

total annual load of P entering the Myall Lakes arises in the Myall River catchment.

Table 3.3. Comparison of Sub-Catchment CMSS calculated nutrient loads - Nitrogen.

Sub -Catchment % Land Area Nitrogen Loadkg/ yr

% of CatchmentNitrogen Load

Myall River Catchment 54.5 96500 69.6Nerong Area Catchment 4.8 5 900 4.3Boolambayte Creek Catchment 11.7 15 300 11.1



Myall Lake (Lake's Edge) Catchment 29.0 20 700 15.0Total 138 400

Table 3.4. Comparison of Sub-Catchment CMSS calculated nutrient loads - Phosphorus.

Sub -Catchment % Land Area Phosphorus Loadkg /yr

% of CatchmentPhosphorus Load

Myall River Catchment 54.5 12 800 79.6Nerong Area Catchment 4.8 440 2.8Boolambayte Creek Catchment 11.7 1 500 9.5Myall Lake (Lake's Edge) Catchment 29.0 1 300 8.1

Total 16 040

3.1.1.2. CMSS estimates of historical and contemporary annual nutrient loads.

When considering the contemporary nutrient loading of the Myall Lakes system it is

important to recognise that the nutrient loading from the catchment to the lake system has

changed considerably over the past 200 years. Consequently, the nutrient regime under which

the lakes’ were subject to prior to European settlement is probably quite different to what is

currently observed. This could be of great significance in setting targets for future nutrient

loads from the catchment.

To put these changes in perspective, a simple comparison can be made between estimates of

nominal nutrient load if the whole catchment were under native undisturbed forest and with

estimates from loadings under the current land uses. From these estimates it can be seen that

nitrogen loading for the lake system has increased approximately ten fold, while phosphorus

loadings have tripled (Figure 3.1).

Myall Lakes Catchment CMSS Model Nutrient Load Comparison.

0

20

40

60

80

100

120

140

160

Nitrogen Phosphorus

Tonn

es p

er Y

ear Pre-1788

Year 2002

Figure 3.1. Myall River Catchment Annual Nutrient Load Comparison (1788 and 2002)



3.1.1.3. CMSS estimates of nutrient source arising from different land uses.

Estimates of nutrient loads from various landuses have been developed from published

information relating to those landuses. Landuse is recognised as a good overall predictor of

nutrient load potential (Young et al. 1995). A limitation with such methodology however, is

that it does not deal explicitly with individual site characteristics, but instead creates relative

comparisons between land use types. For this reason the estimates derived for various

landuses in the Myall catchment should not be regarded as absolute, but rather, as a guide to

which particular landuse may be contributing a relatively higher nutrient load to the lake

system.

In Table 3.5 a comparison of estimated nutrient loads from individual land uses is presented.

From a catchment management perspective, knowing the magnitude of loads arising from

different landuses provides invaluable information. This data can then assist in the targeting

of strategies to reduce loads from specific sources.

Table 3.5 .CMSS derived land use annual nutrient loads from the Myall LakesCatchment. (NB. Bulahdelah STP was upgraded in the 1990s – prior to this it would have releasedrelatively higher P and N loads).

Landuse Percentage ofcatchment area

Percentage ofNitrogen Load

Percentage ofPhosphorus Load

State Forest 32.5 29.0 19.8

Privately held forest lands 20.2 18.0 10.2National Park (native vegetation) 19.4 17.0 7.9Poultry - assuming litter is spread

on-site.Less than 1% 13.0 31.2

Grazing -Native Pasture 13.1 11.0 9.9Grazing -Improved Pasture 1.3 5.0 10.2

Dairy Operations Unkown - small 5.0 5.0

Urban 0.2 1.0 1.3Rural Residential 0.3 1.0 1.0

Other 0.3 Less than 1% 2.5Roads and Easements 0.2 Less than 1% 1.0

Bulahdelah STP Less than 1% Less than 1%

NPWS Tourism Unknown Less than 1% Less than 1%Water (Rivers and Lake area) 12.5 Unknown UnknownTotal Nutrient Load (kg/yr) 138, 400 16, 040

To provide an assessment of accuracy of the data generated by the CMSS modelling field-

validations were undertaken which included catchment water quality sampling and event-

based load measurements.



3.1.2. Estimates of nutrient load from River volume.

An estimate of the annual nutrient delivery (TN and TP) by the Myall River system was

developed from the water nutrient concentration data collected for the Myall River at

Bulahdelah and estimates of annual flow of the Myall River. A limitation of such an estimate

is that it will underestimate the true nutrient loading because of the non-normal distribution

(skewness) of the data. That is, infrequent flood events may import disproportionately larger

loads than can be predicted by these measurements. The estimates of annual river nutrient

loads provide only rough values however they give a means to verify the estimated loads.

Results of these estimates are shown in Table 3.6 below.

Table 3.6. Empirical estimates of annual Myall River TP and TN load to Myall Lakes.

Analyte EstimatedAnnual

DischargeML (106 L)

Median AnnualConcentration

(mg/l)

Estimated Annual loadof (Tonnes / yr)

Total Phosphorus 0.117* 15.5 (TP)

Total Nitrogen

133 000**

0.7* 93.1 (TN)

*Unpublished DLWC data (1999 – 2002).

** From Myall Lakes and Port Stephens Estuary Process Study (MHL 1999).

When comparing this flow estimated nutrient load with data generated by CMSS it can be

seen that there is general agreement between the two methods.

3.1.3. Measured Nutrient Exports from the Catchment - autosampler results

To provide field verification of the CMSS modelling results a storm event sampling program

was undertaken to report on rain event nutrient loads. In late 2000 an auto sampler was

installed at the Bulahdelah flow-monitoring site with sampling triggered by rainfall and / or a

change in river height.

Water samples were collected and analysed for four rain events over the period January 2001

- June 2002, samples being collected every 2 hours for the duration of the event. A summary

of measured results from these events is shown in tables below.

Table 3.7. Summary results from several rain event sampling - Myall River atBulahdelah.

Date Rainfall(mm)

River Flow(ML)

Event PhosphorusLoad (kg)

Event NitrogenLoad (kg)

11 -12th February 2001 25 330 4 21



20-22nd February 2001 55 3400 1170 6500

6 - 11th March 2001 267 32333 9400 45100

1- 13th February 2002 266 32632 2400 21000

Results from this rain event sampling have helped to quantify the magnitude of nutrient loads

from the catchment. In large (over ~100 mm) rain events there is a disproportionate increase

in the load of nutrients transported from the Myall River catchment into the lake system. The

quantities of nutrients measured during these storm events are consistent with predicted

quantities estimated by CMSS modelling, and thus provide validation of the modelled results.

It is apparent from the results summary in Table 3.7 that there were large differences in the

quantity of nutrients delivered to the lake during two events of similar size. In the rain event

of 1- 13th February 2002 and 6 - 11th March 2001 similar quantities of rainfall fell (approx 260

mm). Nominal riverine nutrient loads however were considerably higher in the March 2001

event, most probably caused by the greater intensity of rainfall in this event. The 260 mm rain

in March 2001 being recorded over a five day period, where as the rainfall in the February

2002 event was recorded over a 10 day period. Factors such as the intensity of rainfall, the

time since last flood (eg. an intense storm following prolonged drought will deliver more

nutrients than a storm following recent flooding, because more nutrients will have available in

the landscape), and duration of rain event, will all influence the processes which mobilise

nutrients into the river system and the amount delivered.

3.1.4. Results from Water Quality Monitoring in the Myall River .

Monthly water sampling has been undertaken by DIPNR as part of a broader program to

investigate river health in the river systems of the Lower North Coast. The program reports on

a variety of parameters at end-of-system monitoring sites for major rivers in the Lower North

Coast Catchment area. The sampling program has been designed to provide general

information on river nutrient levels, catchment loads and changes in condition over time.

For the Myall River catchment sampling is undertaken on the Myall River at Bulahdelah

Bridge where continuous river height monitoring equipment is installed. A summary of the

findings from samples collected 1/1/2000 - 30/6/2002 are presented below (Table 3.8 and

Table 3.9).



Table 3.8. Summary of physical water quality characteristics.

ParameterStatistic

ElectricalConductivity

(µS/cm)pH

Turbidity (NTU) Temperature

Number of samples 30 30 30 28

Mean 825 6.9 22.1 20.3

Minimum value 79 6.2 2.9 11.4

Maximum vale 4999 7.7 107.0 28.7

S.D. 1035 0.3 22.9 4.7

Median 284 6.9 13.6 20.8

The physical water quality characteristics are consistent with characteristics of streams in the

Lower North Coast area. The pH values recorded reflecting the acid to neutral status typical

of coastal stream systems. The median turbidity value was found to be 13.6 NTU with the

colouration present generally arising from humics of dissolved organic matter. The electrical

conductivity readings were generally low, however some higher values were recorded in the

drier times. In late 2002 saline water was observed intruding up the Myall River as far as

Bulahdelah Bridge which is thought to be the approximate limit for the Port Stephens salt

wedge.

Table 3.9. Summary of riverine nutrient concentrations.

Parameter

NOx Nitrogen(mg/L)

Total Nitrogen(mg/L)

FRP -Soluble P

(mg/L)

TotalPhosphorus

(mg/L)Number of samples 30 30 29 29

Mean 0.048 0.687 0.035 0.097

Minimum 0.000 0.420 0.002 0.024

Maximum 0.180 1.270 0.141 0.281

S.D. 0.044 0.217 0.031 0.058

Median 0.040 0.690 0.031 0.096

The median total phosphorus level was found to be 0.096 mg/L. The SRP (soluble reactive

phosphorus - the soluble phosphorus component that is most readily used by plants and algae)

was found to be 0.031 mg/L with this representing some 32% of the phosphorus present. The

median total nitrogen value was found to be 0.69 mg/L with the NOx nitrogen value of 0.04

mg/L. The soluble NOx component representing around 5% of the nitrogen present.

In Figure 3-2 a plot of the monthly results of total nitrogen and total phosphorus is presented

from samples taken from the Myall River at Bulahdelah. It can be seen that over the

monitoring period a large variation in the Total Phosphorus and Total Nitrogen concentrations



were recorded, reflecting the influence of rainfall on nutrient concentration and loads. The

graph however shows a general parity between changes in riverine total nitrogen and total

phosphorus concentrations.

Figure 3.2. Monthly TN and TP concentrations for Myall River at Bulahdelah.

There is a strong correlation between river total nitrogen and total phosphorus concentrations

r2 = 0.91 (Figure 3.3). This suggests, as might be expected, that the transport processes

relating to the movement of these nutrients are related.

Correlation Matrix for Total Nitrogen vs.Total Phosphorus Myall River at Bulahdelah (Jan 00 -June 02)

TOTAL_P = -.0720 + .24571 * TOTAL_NCorrelation: r = .91254

Total Nitrogen mg/L

Tot

al P

hosp

horu

s m

g/L

0.00

0.06

0.12

0.18

0.24

0.30

0.3 0.5 0.7 0.9 1.1 1.3 1.5

Regression95% confid.

Figure 3.3. Correlation of riverine TN and TP concentration at Buladelah.

Myall River at Bulahdelah Total Phosphorus and Total Nitrogen Concentrations

Jan 00 - June 02

00.05

0.10.15

0.20.25

0.3

Jan-

00

Mar

-00

May

-00

Jul-0

0

Sep

-00

Nov

-00

Jan-

01

Mar

-01

May

-01

Jul-0

1

Sep

-01

Nov

-01

Jan-

02

Mar

-02

May

-02To

tal P

hosp

horu

s m

g/L

00.20.40.60.811.21.4

Tota

l Nitr

ogen

mg/

L Total P Total N



3.1.5. Atmospheric Nutrient Contributions

In rainfall there is a small nutrient component present, often associated with airborne dust and

soil particles being washed down in the first flush of rainfall. These small quantities when

considered over such a large surface area such as 100 km2 of the Myall Lakes system could

make a significant annual contribution to system’s nutrient load.

Analysis from coastal rainfall (Data from metrological station at Lake Ainsworth North Coast

NSW) found total phosphorus concentrations of around 0.01 mg/L Total P. Annual rainfall

for Bulahdelah is around 1328 mm year and the lake surface area approximately 100 km2.

This equates to an atmospheric delivery to the lake of 1330 kg Phosphorus / yr.

Data for rates of atmospheric Nitrogen deposition in the southern hemisphere identify a range

of between 50 -150 kg / km2 / year (Harris, 1999). For the purposes of this assessment the mid

value of 100 kg/ km2 /year will be used. From these figures an estimate of 10 tonnes per year

was delivered based upon a surface area of 100 km2. These levels are considered insignificant

compared to other sources.

3.1.6. Potential nutrient contribution from National Park visitor sewage waste

When the blue green algal bloom was first detected in Myall Lakes, the initial reaction of

many people familiar with the lake system was to assume that the more obvious sources of

nutrients, such as waste-water treatment facilities on the lake’s foreshore, were the main cause

of the bloom. To place in perspective the potential nutrient load arising from tourism-

generated sewage an assessment, which assumed that all toilet waste and grey water

ultimately found its way into the lake’s waters (ie. worst case scenario), was performed. The

theoretical assessment shown in Table 3.10 concluded that fairly small contributions would

arise (less than 5%), in comparison to the catchment load estimates for nitrogen and

phosphorus that are also represented in Table 3.3 and Table 3.4.

Table 3.10. Potential nutrient load from visitor sewage estimates in comparison withcatchment loads

Site Nitrogen kg / yr Phosphorus kg / yrTotal direct waste input 2, 089 646

CMSS Estimate of catchmentload

138, 400 16, 040

3.1.7. Estimated Phosphorus load from Groundwater inflows

No nutrient load estimates from groundwater were undertaken as part of this project. However

Manly Hydraulics Lab (MHL) estimated the rate of ground water inflow into the lake system

as part of the Myall Lakes and Port Stephens Estuary Process Study (MHL 1998). Estimates



were developed based on published information describing the hydraulic conductivity of

similar aquifer types, and assume a high hydraulic gradient. Loads were calculated for

phosphorous, but not for nitrogen. Results of the MHL phosphorous load estimates are

presented in (Table 3.11), however in light of further groundwater work, it is regarded that

these are likely to be an over-estimate and further work is required to provide reasonable

certainty for load figures.

While no verification of the nutrient flux data has been performed and the figure of 4.7 t/year

is not intended to be an accurate measurement, it provides a ‘ballpark’ maximum figure of

annual groundwater phosphorus load based on some fairly coarse estimates. The wastewater

component of this figure (assuming all human waste is discharged directly into the lake) is

relatively small (see section 3.1.6).

Table 3.11. Estimate of annual groundwater phosphorus load. Based on inflow ratesdeveloped by MHL in Port Stephens and Myall Lakes Estuary Process Study (1998).

Analyte Maximum possible Annual Load(Tonnes)

Total Phosphorus 4.7*

* Tidal/ seasonal influence will possibly change loadings, with the movement (loss) of phosphorous togroundwater system possible when outflows from the lake to the aquifer system occur.

3.1.8. Estimate of Myall Lakes System nutrient loading per unit lake surface area.

The Myall Lakes system is estimated to have a water surface area of approximately 100 km2.

When considering nutrient loading impacts it is important to consider the physical

characteristics of the estuary system. A shallow waterway with a large surface area for

example, can accommodate a greater nutrient load than a waterway of the same volume, but

lesser area. In theory, the greater area available for denitrification in the shallower waterway

will cause a lesser loading of organic carbon and greater denitrification efficiency, all else

being equal. The measure of nutrient load delivered per unit area can thus assist in describing

the nutrient status of a waterbody. Table 3.12 below presents estimates of nutrient loading per

surface area of lake system currently, and pre-European settlement.

Table 3.12. Estimated annual catchment nutrient load for Myall Lakes.

NitrogenTonnes /km2/year

PhosphorusTonnes /km2/year

CMSS Estimate pre 1788 0.1 0.05CMSS Estimate 2002 1.38 0.16

Chapter 4, Phytoplankton Abundance and Distribution Understanding Blue Green Algae Blooms in Myall Lakes NSW.

NSW Department of Infrastructure, Planning and Natural Resources45

4. Phytoplankton Abundance and Distribution

4.1. BACKGROUND

Phytoplankton is the collective term used to describe mainly unicellular algae less than 50?m

in diameter that live within the water column, but may have a resting stage or spore cycle

within the sediments. Some of the larger colonial forms may possess individual cells of

uniform structure within filaments, chains or loosely bound cells within mucilage.

Identification of these species is based on the cell shape, cell dimensions, cell wall

composition, mucilage layers, chloroplast structure, flagella and storage mechanisms (Boney,

1988). On the basis of these physical characteristics phytoplankton are grouped into classes.

The major classes covered in this report are:

1. Blue-green algae (Cyanophyceae);

2. Diatoms (Bacillariophyceae);

3. Dinoflagellates (Dinophyceae); and

4. Green algae (Chlorophyceae).

Along with macroalgae and macrophytes, phytoplankton is a principal source of primary

productivity (organic material) in aquatic ecosystems, and forms the basis of food webs. This

primary productivity of phytoplankton is dependant on adequate light, inorganic carbon,

dissolved mineral nutrients, suitable salinity, water and suitable ambient temperature to

sustain metabolism (Boney, 1988). The particular interaction of these limnological conditions

and the morphology and ecophysiology of phytoplankton species (by virtue of their size,

shape, habitat/niche preference, nutrient requirements, movement abilities) determine the

distribution and persistence of particular classes and species of phytoplankton. Consequently,

phytoplankton community composition can reflect strongly the physical and chemical

characteristics of a water body.

4.1.1. Phytoplankton community as an indicator of estuarine health.

A change in species richness and an increase in the abundance of phytoplankton is often

associated with eutrophication. Globally, Anderson et al., (2002) reported strong correlations

between total phosphorus input and phytoplankton production in freshwaters, and total

nitrogen input and phytoplankton production in marine waters. As well, they noted that

blooms of blue-green algae in estuarine and brackish coastal waters in Australia and



Scandinavia have also been linked to phosphorus enrichment. So, enrichment both of these

macronutrients can play a role in exacerbating estuarine algal blooms.

Commonly, green algae (Chlorophyceae) and blue-green algae dominate the phytoplankton in

degraded systems (e.g. Boney 1988). It is thus possible to use the observed occurrence,

biomass and extent of phytoplankton as good bioindicator of trophic status of water bodies.

The response of phytoplankton to changes in water quality however, is not necessarily linear

or easily interpreted.

While the general principles underlying algal blooms are reasonably well understood, the

reliable prediction of algal blooms in rivers, estuaries and coastal waters with complex

mixing, circulation and flushing remains an inexact science (Anderson et al., 2002). The

competitive interactions between algal species as well as many other biological factors (eg

presence or abundance of grazers, water clarity / nutrients, and weather conditions), which are

rapidly changing, interact to determine the composition of the dominant phytoplankton

community.

This report focuses mainly on blue-green algae due to the development of the potentially toxic

bloom of Anabaena circinalis and Microcystis aeruginosa in April 1999 in Myall Lakes.

4.1.1.1. Changes in phytoplankton community and ecological succession.

Any ecological community present somewhere at a point in time is not only a result of the

environmental conditions that currently prevail, but is also a consequence of the conditions

and organisms that preceded its occurrence (Krebs, 1985). Consequently, while the

requirements of a particular taxa might, in principle, be ideally suited to the observed

conditions another seemingly inferior taxa may actually predominate because of the sequence

of events or conditions that have occurred previously. This principle, that the sequence of

events (the succession) are as important as the current conditions is one of the tenets of

ecology and is important in describing the observed changes in the phytoplankton community

in Myall Lakes.

Phytoplankton succession is thought to be, in part, attributable to changes in ratios of

nitrogen, phosphorus and silica (Anderson et al., 2002), changes in flow conditions causing

steep environmental gradients (Fabbro & Duivenoorden, 2000), and the differential effects of

these and other physical, chemical and biological factors on individual species (Hallegraeff &

Reid, 1986). Coastal lakes are physically dynamic systems (changing due to rainfall, tidal

flushing etc.) and the phytoplankton in these places also changes rapidly in response. The

algal taxa that dominate at one point in time, perhaps in response to a large disturbance or



brief event, can modify the environmental conditions (e.g. nutrient regime) to change the

community composition that occurs later (Krebs, 1985). Consequently there is often a

stochastic component that plays an unknown role in algal ecology.

While there may be spatial and temporal differences imposed on phytoplankton succession in

flowing rivers, reservoirs, coastal lakes, estuaries and the sea, the patterns of development and

trigger mechanisms for algal blooms appear to be universal. For example, according to

Hallegraeff & Reid (1986) the species patterns in the sea off Sydney on the east coast of

Australia resemble spring and autumn patterns experienced in European waters.

On the east coast of Australia peaks in phytoplankton abundances in oceanic waters are often

related to nutrient enrichment through periodic upwelling of deep ocean waters which are

high in nutrients. Although upwellings occur throughout the year, marked changes in

phytoplankton assemblages can be initiated in Spring with the appearance of high numbers of

small chain-forming diatoms, followed by larger centric diatoms in November and later by

dinoflagellates. Diatoms decline in abundance towards the end of summer reappear in late

summer and early autumn again followed by an abundance of large and small dinoflagellates.

In fresh waters the succession is similar with Boney (1988) reporting spring outbursts of

diatoms (due to their capability for rapid cell division, and high photosynthetic rate) in

response to increasing photoperiod and high nutrient concentrations. These are then followed

by slower growing and larger diatoms, then dinoflagellates and other organisms with slower

growth rates such as green algae and blue-green algae.

The summer conditions of higher temperatures, lower nutrients and water stability enable

slower growing green algae and blue-green algae to compete with diatoms, that grow quicker

in cooler waters. This has been demonstrated in the Peel Harvey Estuary in Western Australia,

where blooms of diatoms were common in winter after river inflows, and blue-green algae

(Nodularia ) growth limited by temperature in winter, invaded in summer. However this only

occurred if winter riverflows had decreased salinity to levels conducive to Nodularia.

Increased salinity was also found to contribute to a decrease in Nodularia (Lukatelich &

McComb, 1986).

Climate variability was also found to have major impacts on seasonal and interannual changes

in dominant phytoplankton biomass in Lone Pine Dam in Queensland. This was due to

variations in inflows (nutrient and silica inputs) that were correlated with the Southern

Oscillation Index cycle (El Niño) (Harris & Baxter, 1996). In general it was found that there

was an inverse relationship between diatoms and blue-green algae with the two rarely



coexisting. Diatoms dominated under mixed conditions while blue-greens dominated during

calm periods.

4.1.2. Some Characteristics of Blue-Green Algae

Freshwater blue-green algae (Cyanophyceae) are a type of photosynthetic bacteria

differentiated from other algae by (Fogg et al., 1973):

? their carbohydrate storage of glycogen;

? cell wall composition of saccharides; and

? photosynthetic pigments of chlorophyll - ? , carotenoids and phycobilin.

Within the class are orders that are defined by their shape cell dimension, structure, motility

and presence of specialised cells (Baker & Fabbro, 1999). Across these orders, species can be

characterised further according to their ecostrategies or habitat preference (eg: planktonic or

benthic [Chorus & Bartram, 1999]) and the type of toxin they produce. Blue-green algae are

rarely dominant but tend to be opportunistic species that have adaptations that allow them to

exploit a certain set of resources and conditions, and out-compete other phytoplankton under

such conditions.

4.1.2.1. Adaptations of Blue-Green algae:

Blue-green algae are primitive algal cells and are generally not able to routinely out-compete

other groups in healthy waterways. However, they posses a number of adaptations that allow

them a competitive advantage in degraded waterways:

1. The possession of low energy requirements to maintain cell functions, when compared to

other groups;

2. The presence of gas vacuoles in some taxa, and additionally the formation of large colonies

or chains that make the cells of some taxa (e.g. Anabaena and Microcystis) very buoyant.

These taxa often form scums in the calm after a windy period due to buoyancy

overcompensation. Buoyancy regulation allows the colonies to maintain their position

within the water column at optimal levels for photosynthesis (Fay, 1983). This is

particularly an advantage in turbid waters, and where vertical mixing is low.

3. Blue-green algae also possess accessory pigments such as phycocyanin and phycoerthyrine

that allow the cells to photosynthesise in lower light conditions compared to other



phytoplankton. This along with point 2 above favours these cells in turbid waters

(Bowling & Baker, 1996).

4. The ability to switch between autotrophy (photosynthesising) to heterotrophy (consuming

other organisms) which allows some species to overwinter on the bottom of lakes or

survive during periods of low light availability (e.g. Microcystis).

5. A substantial storage capacity for phosphorus, allowing species to load phosphorus when it

is not limited. This storage capacity enables species to perform two to four cell divisions

resulting in a thirty two fold increase in cell numbers (Chorus & Bartram, 1999).

6. The production of akinetes or spores (by some species) allows viable populations to be

maintained in sediments for many years until suitable conditions to bloom again

eventuate.

7. Some species of blue-green algae have the ability for nitrogen fixation and produce

specialised cells (heterocysts) to facilitate this (eg Anabaena). However these heterocysts

are only developed in the absence of suitable levels of combined nitrogen in the water

(NHMRC, 1984) and some other species are also thought to fix small amounts of

atmospheric nitrogen (Microcystis). This fixation and the ability to also liberate

substantial quantities of extra cellular nitrogenous compounds (Fogg et al., 1973: Rai,

1997), means that nitrogen does not limit the occurrence of some species, and the

ammonia secretion probably assists in maintaining stable populations once the bloom has

developed.

4.1.2.2. Ambient conditions that enhance blue-green algal growth:

Although the adaptations of blue-green algae mentioned above are substantial, they do not

provide a competitive advantage over other phytoplankton in pristine waterways. To enable

blue-greens to become dominant a change in ambient water conditions towards the following

is required:

1. High nutrient concentrations,

2. Low salinity,

3. Warm waters (to increase growth rates),

4. A change in turbidity from ambient levels,



5. Calm water conditions and stratification. Lack of vertical mixing can cause other algae to

sink out of the illuminated water column, while buoyant blue-green algae can remain near

the surface.

6. Low amounts of grazer predation. This may in part be enhanced by the toxins produced by

the cells.

7. Low numbers of phytoplankton competitors. This will allow the cells’ low growth rates to

be less disadvantageous, as nutrients are not monopolised by other algae.

It is clear that while blue-green algae are primitive organisms and have inferior competitive

abilities under most conditions, at times water conditions exist that favour these algae over

other types. Often, the changed conditions associated with the degradation of waterways are

ideal conditions for these cells, so disturbances in a waterways catchment can be reflected in

changes in the phytoplankton community to include a greater proportion of blue-green algae.

The response is not always so predictable however, the initial algal assemblage, the presence

of elevated nutrient concentrations and complex interactions of the above limnological

conditions are required to enable bloom development (Mitrovic & Bowling, 1996).

4.1.2.3. Human Health implications of Blue-Green algae.

Human health concerns over the presence of blue-green algae are due, in part, to the presence

of lippopolysaccharides in all taxa. These are contact irritants posing health threats to

recreational water users. Although there are limited studies on the effect of these contact

irritants, epidemiological studies by Saadi et al. (1995) and Pilotto et al. (1997) identified that

dermatological and gastrointestinal symptoms were linked to increased cell numbers of blue-

green algae.

Toxins (also odour and taste compounds) are produced by some species, that upon ingestions

can cause serious human health problems (NHMRC,1994). Microcystin toxin, which is

produced by some species of Microcystis, has a hepatotoxic effect (damaging the liver).

Others have a neurotoxic effect (affecting the nervous system) such as saxitoxins or paralytic

shellfish poisons produced by some species of Anabaena. The bloom of Anabaena and

Microcystis in the Darling River in 1991 caused numerous stock deaths in animals that had

consumed contaminated water (Blue-Green Algal Task Force 1992). Other species are also

known to produce cytoxins (e.g. Cylindrospermopsin) that have an effect on a number of

internal organs (Burch & Nicholson, 2000).



While the presence of blue-green algae is a health concern to recreation, particularly if

directly swallowed, some toxins also have the potential to accumulate in high concentrations

within shellfish, prawns and in the muscle of fish (Falconer & Choice, 1992). So the presence

of blue-green algal toxins in waterways can affect human health through direct contact or

through the consumption of contaminated seafood, which can swim to, and be consumed from

waterways unaffected by algal blooms.

4.2. METHODS

4.2.1. Aims of the monitoring study

The aims of monitoring blue-green algae, and the analysis of the phytoplankton data were two

fold:

1. To ensure adequate warnings to the public in response to high cell counts of potentially

toxic and non toxic algal species, through implementation of the Regional Algal Contingency

Plan (MKGLRACC, 2000). This program was initiated in 1999.

2. To develop an understanding of the ecology of phytoplankton in Myall Lakes, and utilise

algal assemblages as indicators of estuarine health. Aspects covered include the spatial and

temporal distribution (and the factors influencing this), and community dynamics.

4.2.2. Algal sampling and Analysis

Sampling was carried out by NPWS and DIPNR staff in accordance with the ‘Draft National

Protocol for Monitoring of Cyanobacteria and their Toxins in Surface Waters (ARMCANZ,

1997) using a 2m integrated water column sampler. Prior to 2001, sampling frequency varied

depending on the species present and cell counts, in accordance with state guidelines for

recreational waters. This information was initially collected for the purpose of initiating and

lifting public health warnings, so sampling intensity varied depending on extent and type of

algae present creating numerous data gaps in early records. Total algal counts were performed

on the samples by NATA1 accredited laboratories for algal enumeration that guarantees

accuracy for abundant taxa of +/- 20% (this is standard across the nation).

From January 2001 total phytoplankton counts and biovolumes were measured in accordance

with revised state guidelines for recreational waters with the frequency again depending upon

requirements of the Algal Contingency Plan but occurred at least on a monthly basis at up to

ten sites. Retrospective calculations were made to determine biovolumes based on cell counts

prior to January 2001. There is a small risk that unknown temporal or spatial differences in



cell sizes and colonies may result in inaccurate biovolumes for the period prior to January

2001, but these differences are likely to be trivial.

After simultaneous testing by three laboratories between January and May 2000, a change of

testing laboratory was made due to its greater ability to detect blue-green algal species with

smaller sized cells and perform counts of all algal taxa (not just blue-greens).

4.2.3. Data Analyses and presentations.

Although the Coast and Clean Seas project commenced in September 2001, the algal data

collected from April 1999 are incorporated into this report to demonstrate the significant

change in the composition of the phytoplankton assemblage in Myall Lakes between 1999

and 2002.

The average biovolumes (mm3/L) or cell counts (cells/mL) for the eight most abundant genera

of blue-green algae at sites within four regions (River Mouth, Broadwater, Two Mile Lake

and Myall Lake)) were graphed to exhibit temporal and spatial changes from April 1999 to

September 2002. The average total biovolume of toxigenic (Anabaena, Microcystis,

Aphanizonomon) and non toxigenic species were also graphed in these regions to show the

variation in potential toxicity of the algal community over time. Additionally, for the period

from March 2001 to September 2002 the average total phytoplankton biovolumes for four

main families (Bacillariophyceae, Chlorophyceae, Cyanophyceae, and Dinophyceae) were

graphed to show the temporal and spatial variation of all phytoplankton.

Multivariate analysis of the eight blue-green algae genera, and separately all phytoplankton at

the genus level, was used to elucidate patterns of similarity in assemblage composition. A

similarity matrix was constructed using cell counts from individual samples (cells/mL) as this

avoids any error introduced by incorporating the retrospectively calculated biovolume data.

Although most of the high outliers had been removed, the data included many zero values and

occasional high cell counts. The data was transformed to the fourth root and a similarity

matrix of Bray-Curtis index scores was constructed. A cluster analysis was performed using

the similarity matrix to produce dendrograms. Group-average linkage was used in the

clustering technique so that the average dissimilarity between groups was used in the

algorithm. An ordination was performed on the similarity matrix using non-metric multi-

dimensional scale (n-MDS) techniques. The samples were plotted in three dimensions and the

1 National Association of Testing Authorities.



procedure repeated ten times so that the plot with the lowest distortion was used. Samples

were labelled in the year taken and season taken to identify any seasonal or temporal trends.

Spatial maps of average monthly total blue-green algal biovolumes were created using

geospatial software (GIS) to visually show the extent of the blue-green algae bloom over the

study period.

Scatterplots of Electrical Conductivity against the logarithmic total algal cell count for five

genera for sites at The Broadwater, Bombah Point, Korsemans Landing, Violet Hill and Myall

Lake were plotted. The data from April 1999 to April 2002 were plotted to show the effect of

salinity in selecting algal species and influencing cell abundance over a period of great spatial

and temporal salinity difference.

Results and analyses from Ryan (2000) were used in discussing results here as they are

particularly focussed on the ecophysiology and morphology of blue-green algae and the

factors leading to the development of the blue-green algae bloom and succession in Myall

Lakes.

4.3. RESULTS.

4.3.1. Spatial Distribution of Blue-Green Algae.

The first indications of a blue-green algal bloom in Myall Lakes occurred in March 1999

when regular lake users noted green scums. These were similar in appearance to the later

confirmed bloom in sheltered embayments around Bombah Point. In early April 1999, a

widespread green slick and pungent earthy odour was reported to the NSW Environment

Protection Authority (EPA) by National Parks and Wildlife Service (NPWS) staff. A sample

was taken and identified as containing high numbers of the freshwater blue-green alga

Anabaena circinalis, a taxon potentially able to produce saxitoxins or paralytic shellfish

poisons that are neurotoxic. This incidence was the first scientifically documented blue-green

algal bloom in the Myall Lakes system, and anecdotal reports from the long-term community

agreed that scum-forming algae was not previously know at the location.

As no regular water quality sampling program was in place prior to April 1999, the status of

water quality and phytoplankton communities within the lakes prior to the blue-green algal

bloom were unknown (Ryan, 2000). This is a common problem throughout Australia with

Bowling (1984) concurring that monitoring of limnological conditions does not occur until a

blue-green algal bloom has developed and as such the pre-bloom conditions that facilitate

such blooms is not well understood.



During the three and half year study period (April 1999 to September 2002) the blue-green

algal bloom was initiated, or first reported, in the Broadwater in high biovolumes (> 2 mm3/L,

see Figure 4.1). Through time, algal blooms were subsequently reported in Two Mile Lake,

Boolambayte Lake and then Myall Lake in April 2000, although different taxa dominated in

each area. (ie. toxic species, such as Anabaena and Microcystis, were generally restricted to

the Broadwater and mid-lakes, while smaller-celled species, such as Chroococcus, dominated

in Myall Lake). High biovolumes were not observed in Myall Lake until October but

decreased thereafter dramatically from February 2001.



Figure 4.1. Myall Lakes Average Total Monthly Biovolumes.

4.3.2. Blue-Green Algal community change and succession

During the three and half year study, the composition of the blue-green algal community

changed dramatically. The use of multivariate analysis (of blue-green algal community

composition, the occurrence and abundance in each sample taken) was employed to identify

the main taxa present in each location as the bloom progressed, and to identify seasonal

changes imposed on the community.

4.3.2.1. Multivariate analysis of temporal and spatial trends in the Blue-Green Algal

community.

Ordination plots (Figure 4.2) highlight the inter-annual variability in the blue-green algal

community as a function of distinct wet (before July 2001) and dry periods (after July 2001).

Each point represents the similarity of a single day’s algal community to other samples.

Seasonal plots were generated but were not included, as the strong inter-annual variability

was greater than any seasonal signal.

1999

2000

2001

2002

Stress: 0.1

Figure 4.2. Temporal Changes in Blue-Green Algal Community Assemblage in theBroadwater April 1999 - October 2002.



1999

2000

2001

2002

Stress: 0.11

Figure 4.3. Temporal Changes in Blue-Green Algal Community Assemblage in MyallLake April 1999 - October 2002.

The high abundance of Anabaena in 1999 and Microcystis in 2000 were major contributors to

structuring the community in the Broadwater. These species were associated with wet periods.

The occurrence of Planktothrix and Coelosphaerium in late 2000 which was then replaced by

algae such as Merismopedia and Chroococcus in mid 2001 produced a change in community

structure during the dry years (2001-02). This was well defined in Myall Lake (Figure 4.3)

with the occurrence of very high counts of Anabaena early in 1999, and then both Anabaena

and Microcystis in 2000.

The clear dichotomy in the algal community structure in 2000 corresponds with the decline of

Anabaena and Microcystis and their replacement by the algal genera, Chroococcus and

Merismopedia. This may be due to changes in the analytic technique to determine cell counts

that occurred around this time. The technique used prior to June 2000 was biased toward

detection of larger algal species. However, the ordination seems to be more affected by a lack

of Microcystis and Anabaena after June 2000, and these results would not have been affected

by changes in laboratory technique. The following sections provide a description of the

changes over time of the blue green algal communities (as illustrated in Figures 4.2, 4.3, and

4.4). Descriptions of these communities are described below and are termed “Phases”, with

Phase 1 being the first detected bloom.

4.3.2.2. Phase 1 - Blue-Green Algal Bloom

The first species detected in April 1999 in the Broadwater was Anabaena circinalis.

Although this species has the potential to produce neurotoxins, none were detected through



toxicity testing (for saxitoxins) towards the end of the Anabaena bloom. Anabaena was not

detected in high numbers anywhere in Myall Lakes after July 2000.

The occurrence of large celled filamentous Anabaena as the primary coloniser (Figure 4.4)

after catchment inflows was found when total phosphorus, phosphate and total nitrogen was

greatest (Ryan, 2002). It is likely during this time that turbidity in the Broadwater was also

high due to catchment inflows, as has been observed subsequently.


In December 1999 Anabaena was again found to be very abundant in the Broadwater and in

Two-Mile Lake. This was later (~ February 2000) replaced by Microcystis aeruginosa that

was found to be producing the hepatotoxin microcystin, in varying concentrations, throughout

the bloom. Like Anabaena, Microcystis aeruginosa has gas vacuoles and forms large colonies

(that enhance their buoyancy), and may produce surface scums that are easily blown by the

wind. After early 2000 both taxa ceased to be dominant in any location in the lakes.



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Figure 4.4. Changes in Blue-Green Algal Community April 1999 – October 2002


The large-celled blue green algal taxa were replaced by Coelosphaerium and species such as

Chroococcus and Merismopedia in mid 2000. The latter species persisted in the upper lakes

(Myall Lake) over the remainder of the study period . It is interesting to note that in the spring

of 2000 the blooms were wholly dominated by Merismopedia until January 2001, (Figure 4.4)

and since that date Chroococcus has been the dominant taxa in those areas sustaining small-



celled cyanophyte blooms. The simultaneous decline of Merismopedia in conjunction with the

sharp increase in Chroococcus abundance, while it may be coincidental closely mimics algal

succession patterns (eg. Boney 1988) reported for other locations. It should be noted that

while the general trend of change from larger celled species to the smaller celled species

appeared to occur in all systems, it was most pronounced in the Broadwater and mid-lakes.

The abundance of any given taxa across the different lake systems also varied substantially. It

should also be noted that the changes from large-celled to small celled species are not

pronounced for Myall Lake and that smaller celled species may have been common in this

area over the April 1999 to April 2000 period.

This apparent succession could indicate the response of the algal community to a disturbance,

which gradually returned to a community, dominated by Chroococcus or could have been the

start of conditions that favoured cyanophytes over other phytoplankton in these locations. It is

impossible to make conclusions however, without more information.

These genera lack gas vacuoles, but because of their small cell and colony size are not easily

sedimented-out like larger colonial algae, and do not produce scums. Small-celled algae

require less energy to maintain cell function than their larger competitors. These taxa are well

adapted to remain homogenously mixed throughout the metalimnion, and are not obvious to

the naked eye even when present in high concentrations.

4.3.3. The response of algal community composition to changing conductivity.

The occurrence of the first potentially toxic bloom in April 1999 in the Broadwater coincided

with the lowest conductivity (or salinity) recorded during the study (less than 2 mS/cm). The

initial bloom followed consecutive high monthly rainfalls (>250 mm) in May 1998,

November 1998 and April 1999 with two daily events of 65 mm and 123 mm on the 1st and

6th of April 1999 (Ryan, 2002). Maps of changes in conductivity throughout the lake and

over time are presented in Chapter 5.

The correlation between observed ambient conductivity and total cell counts for four main

blue-green algal genera of Myall Lakes are presented in Figure 4.7. A clear distinction is

shown between the range of salinities in which Anabaena and Microcystis were found and

that observed for Chroococcus and Merismopedia, the latter being found in waters far more

saline than other taxa.

Previous analysis of these data by Ryan (2002) identified that the spatial distribution of algae

was correlated with decreasing conductivity, and that a trigger for the development of

potentially toxic algal blooms were values below 2 mS/cm. This can be observed in Figure



4.5 for the Broadwater and in Figure 4.6 for Myall Lake, and illustrates that a drop in

conductivity to 2 mS/cm did not occur in Myall Lake until June 2000, after which a rapid

increase in cell numbers was observed. The increase of potentially toxic algae into the middle

lakes and Violet Hill appears to have coincided with declining conductivity. Whether the

mechanism for the increase is due to the transport of cells from the Broadwater or is a

response of in situ algae to fresher conditions or a combination of both is not known.

In the Broadwater, increases in conductivity as a result of low rainfall after December 2000

were followed by dramatic decreases in potentially toxic algal cell counts (Figure 4.4). This

was mirrored two months later in Myall Lake for the homogenous small celled blue-green

algae. However, in Myall Lake the rate of conductivity change was slight in comparison to

the lakes below Violet Hill, which exhibited trends similar to the Broadwater (Ryan, 2002).

Thus, the decreasing photoperiod and lower water temperatures at this time of year (that

disproportionately slow blue-green algal growth rates when compared to other phytoplankton)

may have been more significant in this decline (ie. the decline in Myall Lake) than the

gradually declining conductivity.

Salinity intrusion appeared to be an important factor in decreasing the dominance of

Anabaena and Microcystis (Ryan, 2002). The increase in salinity in the Broadwater of up to

20 mS/cm in December 2000 corresponded to a rapid decline in algal cell numbers and

cessation of the bloom in this part of the lake (Figure 4.5). Salinity increases prior to this

began in August 2000 in the Broadwater and resulted in a change in blue-green algal

community composition with an increased prevalence of small-celled species.

Site 5 Mid Broadwater

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Figure 4.5. Response of Blue-Green Algae to Salinity in The BroadwaterApril 1999 -March 2001, Source: Ryan, 2002.



Site 1 Myall Lake @ Shellys

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Figure 4.6. Response of Blue-Green Algae to Salinity in Myall LakeApril 1999 - March2001, Source: Ryan, 2002.



Figure 4.7. Scatterplots of Total Cell Counts (Combined Myall Lakes) and ElectricalConductivity for 4 Algal Genera April 1999 – April 2001 Indicating the EcologicalLimitation of these Genera to Salinity: Source Ryan (2002).

4.3.4. Descriptions of phytoplanktonic community succession in Myall Lakes.

The previous section discussed blue-green algae only. The next section discusses total

phytoplankton community changes over time and their spatial pattern for the period from

January 2000 to September 2002. As mentioned in Section 4.1 a well described pattern of

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algal succession is known to occur in marine and freshwaters in spring, often responding to

increasing daylight and high nutrient concentrations. A rapid initial bloom of small-celled

diatoms occurs, which are then followed by slower growing and larger diatoms, then

dinoflagellates and other organisms with slower growth rates such as green algae and blue-

green algae. Blue-green algae are thought to also be favoured under calm ambient conditions

and those described previously. However, from early 2001 all algal taxa from the lakes began

to be identified and thus successions after that date only are possible.

4.3.4.1. Upper Myall Rivermouth.

This site experienced diatom blooms for two months in Summer 2000-2001 and Spring 2001

that corresponded with the timing of saline intrusion into the river. Sharp increases in

dinoflagellate abundances were experienced in the upper Myall Rivermouth from Autumn

2002 with a large biovolume (13.5 mm3/L, corresponding to approximately 14,000 cells/mL)

occurring in Spring 2002 and corresponding with salinity intrusion and transient stratification

(see Figure 4.8). Trend analysis normally requires many years of data, so few trends can be(see Figure 4.8). Trend analysis normally requires many years of data, so few trends can be

detected here due to the short study period. However from the limited data it does appear that

diatom and dinoflagellete blooms in the Myall Rivermouth may be associated with saline

intrusion and stratification that may be increasing nutrient fluxes from the sediments (see

Chapters 3 and 5 for more detail).

4.3.4.2. Bombah Broadwater.

The Broadwater was initially characterised as a community dominated by toxigenic blue-

green algae in autumn and winter of 2000 that followed a large rainfall event in autumn. The

composition of the phytoplankton community prior to this and the pre 1999 bloom are

unknown.

After this time the community composition in the Broadwater changed (Figure 4.9) and was

less dominated by blue-green algae, but exhibited some features of phytoplankton succession.

Small increases in diatom abundance were observed in winter of 2001, followed by a large

green algae bloom the following spring and a smaller blue-green algae bloom. Small increases

in dinoflagellate abundance were observed in the summer of 2001-2002, after a decline in

green and blue-green algal abundance, and an increase in conductivity in the lake. The marine

genus Gymnodinium predominated, of which a number of species can produce paralytic

shellfish poisons or neurotoxic shellfish poisons, but species-level identification was not

determined on this occasion.



4.3.4.3. Two-Mile and Boolambayte Lakes.

The phytoplankton composition in the Mid Lakes was similar to the Broadwater in that it was

dominated in Winter 2000 by blue-green algae. In contrast to the Broadwater, a peak in

diatom numbers preceded this blue-green algae bloom in autumn following the autumn

rainfall. Small peaks in diatom abundance were also observed in spring and summer 2000-

2001 and low biovolumes of blue-green algae followed decreases in diatoms in summer -

again reflecting what was occurring in the Broadwater. Peaks in diatom abundance were

observed again in autumn and winter of 2001 after which a succession of green algae and

blue-green algae followed through spring and summer (see Figure 4.8).



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Figure 4.8. Changes in Phytoplankton Community April 2000 - October 2002.



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Figure 4.9. Temporal Changes in Phytoplankton Community Assemblage in theBroadwater 2000 – 2002 Contrasting a Wet and Dry Phase

In contrast to the Broadwater, the Mid-Lakes exhibited higher numbers of diatoms but a less

dramatic green algal bloom, which followed the autumn rainfall events and coincided with a

drop in conductivity. Similar to the Broadwater, no peaks were observed throughout the

summer of 2002 and till the end of the project period (October 2002).

4.3.4.4. Myall Lake.

Community composition in Myall Lake in autumn 2000 (prior to the drop in conductivity in

September 2000) was dominated by a high abundance of diatoms. The phytoplankton

composition in Myall Lake exhibits high inter-annual variation (Figure 4.10) that seems to be

due to the occurrence of small celled blue-green algal species in 2001 and a high species

richness of diatoms. Small celled blue-green algae were not present in many samples in 2000,

compared to 2001 and 2002, while a high richness of diatoms were present in 2000, compared

to 2001, although they were actually more abundant at the beginning of 2001.

At the beginning of summer 2000-2001 a small peak in diatom abundance occurred, after

which blue-green algae dominated the phytoplankton composition in mid to late summer. A

smaller diatom peak was observed the following winter (2001) in Myall Lake. This was

followed by an algal succession (small diatoms ? larger diatoms ? dinoflagellates), that was

also occurring in the Broadwater and Mid-Lakes. Later a green algal bloom of very high

biovolume (10.5mm3/L) in Spring 2001 occurred, followed by a blue-green algal bloom in

summer 2001-2002. In the following autumn and winter of 2002, no increase in diatom

abundance occurred in Myall Lake or any other part of the Lakes, apart from a small peak in



the Rivermouth. One possible mechanism that may be keeping diatom abundance lower in dry

weather is the exhaustion of silica in the water column causing growth limitation.

2000

2001

2002

Stress: 0.16

Figure 4.10 Temporal Change in Phytoplankton Community Assemblage in Myall Lake2000 – 2002 Contrasting a Wet and Dry Phase

4.3.4.5. Some observed patterns of phytoplankton diversity and abundance.

Diatoms: The general spatial trend throughout the monitoring period was for decreasing

richness of diatoms from the Rivermouth to Myall Lake,. Temporally, the number of diatoms

declined between 1999 and 2002, corresponding to a decrease in freshwater inflows

(particularly in the Broadwater and mid-lakes) and perhaps indicating silica limitation,

particularly in Myall Lake. The dominant diatom in the Rivermouth, Broadwater and Mid

Lakes was Thalassiosira, a marine genus. This diatom occurred in smaller numbers in Myall

Lake where the population was dominated by the freshwater diatom Synedra.

Green algae: In contrast, green algae richness was highest in Myall Lake with the freshwater

green alga, Oocystis, being the dominant genus. This lake had the most stable conductivity,

and was generally the least saline on average of the lakes. Green algae richness was similar in

the Broadwater and Mid Lakes and was dominated by the marine green alga, Carteria in the

Rivermouth and freshwater green alga, Crucigenia , in the Broadwater and Mid Lakes.

Dinoflagellates: The Broadwater experienced the highest richness of dinoflagellates with the

genera observed mainly found in marine or brackish / marine habitats (e.g. Gymnodinium),

although the highest cell counts were observed in the Rivermouth. This richness decreased

with distance from the marine inflows, and Myall Lake contained a mixture of freshwater and

marine dinoflagellates, dominated by the freshwater alga, Peridinium.



Blue-green algae: Blue-green algal richness was also higher in the Mid-Lakes and Myall

Lake compared to the Broadwater. Over the short monitoring period, Myall Lake was

dominated by a mainly freshwater algal community, but has some representatives of marine

and brackish taxa. In contrast, the algal community in the Broadwater was composed of a

mixture of freshwater and marine species, depending on the salinity status of the time. It is

also clear that Myall Lake has high green and blue-green phytoplankton richness with a

continuing spring bloom of small celled blue-green algae and green algae.

4.4. DISCUSSION.

4.4.1. The role of conductivity in algal community composition change.

Low conductivity appears to be a major prerequisite for the occurrence of larger-celled

potentially toxic species such as Anabaena and Microcystis. Conductivity range, however, is

an important factor in the long term regulation of small celled phytoplankton communities.

In Myall Lakes, salinity or conductivity is a function of the rates of: freshwater inflows from

the catchment or rain; loss of fresh water through evaporation from the lakes; and saline

intrusion from the Port Stephens estuary via the lower Myall River. The stenohaline (small

variation in salinity) character of Myall Lake, (see Chapter 5) appears to be important in

maintaining stable small celled blue-green algal populations. The more variable (euryhaline)

character of the Broadwater, creates a less stable salinity regime which in turn influences the

long-term stability of any given phytoplankton assemblage.

According to Paerl (1988) small shifts in salinity of between 1.5 – 3.5 mS/cm can cause a

dramatic shift in phytoplankton species composition. Previous analysis of algal data with

conductivity, from throughout the lakes, by Ryan (2002) identified that Anabaena and

Microcystis were present when conductivities were less than 6 mS/cm with a preference for 1-

4.5 mS/cm (Figure 4.7). This is supported by Winder (1994) and Winder & Cheng (1995)

who reported between 5 and 7 ms/cm as the ecological limitation for Anabaena circinalis. In

contrast Chroococcus and Merismopedia dominated at conductivities between 1.5 – 10

mS/cm but were persistent up to 27 mS/cm., although in reduced numbers (Figure 4.7).

4.4.2. Patterns of nutrient concentrations and the algal community in Myall Lakes.

Freshwater inflows not only reduce salinity to levels that favour toxigenic blue green algal

species, they also deliver loads of nutrients and sediment to Myall Lakes, and are likely to

cause stratification of the water column. These combined effects of freshwater inflow create

conditions that favour blue green algae over other phytoplankton species. Therefore, locations

within the lakes with the greatest amount of freshwater input (i.e. the Broadwater) are also the



most prone to toxigenic blue-green algae blooms. While it is impossible to separate the effects

of increased nutrients, stratification and reduced salinity, examples of increased abundance of

blue-green algae following rainfall for salt-tolerant taxa have been found in this study. In

March 2000 and February 2001 rainfall events were followed by increased algal cell counts of

Chroococcus in the Broadwater and Mid Lakes, apparently enhancing a bloom that was

already underway prior to the rainfall event (Figure 4.4). The influence of these freshwater

flows on the lake nutrient concentrations are reported in Chapter 5, which discusses far lower

nutrient concentrations in the water column during dry weather, than during a period of

average rainfall. The influence of different nutrient types on algal abundance is discussed

below.

Phosphorus: A clear gradient of highest water column total phosphorus concentration in the

upper Myall Rivermouth and lowest at Neranie at most sampling times, supports the model

that the Myall River is the source of most nutrients to the system. In addition, this part of the

lakes have been found to be periodically stratified (following high catchment inflows) which

could be intermittently facilitating the release of phosphorus from the sediments in cases

when bottom waters become anoxic.

Murray & Parslow (1999) reported that the spatial variation of algal blooms is strongly

influenced by the location of major nutrient inputs, with temporal variation dominated by the

occurrence of catchment runoff events delivering nutrient loads from the catchment. This is

consistent with the occurrence of algal blooms in close proximity to freshwater inflows in the

Peel Harvey estuary in Western Australia (Lukatelich & McComb, 1986), Port Phillip Bay in

Victoria (Murray & Parslow, 1999) and Cockburn Sound in Western Australia (Hillman et al.,

1990).

Various studies (Fogg et al., 1973: Hart et al., 1985) have alluded to nutrient requirements as

the determining factor in succession from Anabaena to Microcystis. Bowling (2001) reported

that Anabaena requires higher ambient phosphorus than Microcystis because it is less able to

utilise phosphorus at low concentrations, and is thus well suited to follow shortly after a

period of high phosphorus. After its addition, phosphorus may be rapidly lost via

sedimentation or consumed by flora and depleted.

Differences in sediment chemistry processes in freshwater compared to brackish and marine

systems mean that phosphorus is less likely to be a limiting nutrient in brackish systems

compared to freshwater systems. In this study low concentrations of phosphorus in benthic

material (in comparison to nitrogen) were found in the Mid Lakes and Myall Lake. This may

suggest that productivity in Myall Lake is limited by phosphorus.



Nitrogen: A less-clear picture of the role of nitrogen in algal ecology has emerged in the

system. The blue-green algal bloom in Myall Lake from December 2000 (of Merismopedia

and Chroococcus) over the summer not only corresponded with a decrease in conductivity to

less than 2 mS/cm but also followed high ammonia concentrations in Myall Lake that

occurred from April-June 2000 and in December 2000 (see Chapter 5). It is widely thought

that small-celled taxa such as Chroococcus grow disproportionately well in waters that are

readily supplied with ammonia.

4.4.3. Other factors influencing the composition of blue-green algal communities.

Although it is energetically expensive, Anabaena is able to utilise atmospheric nitrogen, when

there is not sufficient in the water column. Extracellular excretion of ammonia from

Anabaena or from cell lysis (after death) may increase the concentration of combined

nitrogen in the water. Bowling and Baker (1996) identified that excretion is a process that

may elevate ammonia concentrations making limnological conditions more suitable for

Microcystis, which is able to accumulate and utilise low concentrations of phosphorus.

It can be concluded that the switch in algal assemblage from larger celled to smaller celled

blue-green algae is related to the periods of high and low freshwater inflows to Myall Lakes..

However, as this analysis has been conducted over a very small time scale in comparison to

the long term processes occurring within the lakes, it is difficult to highlight any long term

trends. This is particularly pertinent given that water exchange within the lakes can be an 800

day cycle, which is longer than the duration of the study.

Although at the time of writing, potentially toxic blue-green algal taxa were no longer

dominant in the lakes, it is possible they will re-occur in the future due to their morphological

features, which gives them an advantage over other species in certain conditions. According

to Harris (1994) it is common for larger celled blue-green algae to dominate phytoplankton

communities when nutrients are in abundance. Due to its large cell size the gas vacuoled

Anabaena, requires higher nutrient concentrations than other species of blue-green algae to

maintain cell function, and cannot dominate when nutrients are scarce. In the absence of high

combined nitrogen Anabaena can grow specialist cells (heterocysts) for nitrogen fixation

(NMHMRC, 1984). It can also produce spore-like akinetes that enable it to regenerate, when

out-competed, until conditions are favourable for the establishment and maintenance of new

populations.

The gas-vacuoled blue-green algae such as Microcystis and Coelosphaerium also have the

ability to over-winter on lake benthos and reanimate as viable cells once photosynthetic rates

exceed those of respiration (Chorus & Bartram, 1999). Consequently, gas-vacuoled algae do



not readily form blooms in winter, as they are less buoyant, while small-celled algae remain

suspended within the water column. Over-wintering Microcystis, if present would be

destroyed by salinity intrusion into the lakes. As discussed previously, the ongoing spring

blooms of Chroococcus and Merismopedia in Myall Lake may persist for some time due to

their winter occurrence within the water column and efficient nutrient cycling, among a range

of other potential influences. The succession of Chroococcus over scum-forming species such

as Microcystis may be related to a variety of factors such as nutrient availability, light

availability, electrical conductivity, water chemistry stability, water column stability and by

virtue of their ecophysiology. The fact that this taxon is not buoyant makes it more suited to

the clearer waters of Myall Lake.

This type of algal species may be able to sustain large populations for extended periods of

time through senescence, efficient nutrient cycling within the water column, (e.g. ammonia

excretion and absorption), and may not be as reliant on external nutrient sources as the larger

species. It is likely that the presence of Chroococcus (although in this instance it seems to

have been facilitated by taxa that need high nutrient concentrations) might not necessarily be

an indication of elevated nutrients in Myall Lake. Once established and present throughout

winter within the water column, Chroococcus would have a competitive advantage over other

algae due to efficient nutrient partitioning and will undergo an increase in abundance in

Spring when conditions become more favourable (Ryan, 2002). Chroococcus has the ability

to scavenge Nitrogen (N) compounds from the water column. Chapter 5 discusses the

potential links between the abundance of these smaller celled species of blue green algae and

available N. This helps explain the patterns of abundance observed in spring 2000, 2001 and

2002.

Also influencing the recurrence of blooms is the ability of Anabaena to produce akinetes as

resting spores. These may be tolerant to salinity and can survive for many years in sediments

(Fay, 1983). Baker (1999) identified that akinetes in the Murray River provided the inoculum

for bloom development, but required germination conditions that depended on the interaction

of a number of environment factors including increased light availability, water temperature

and elevated nutrients. This may represent a potential future problem for the Broadwater,

where the abundance of these taxa was greatest.

Chapter 5, Water Quality Understanding Blue Green Algae Blooms in Myall Lakes NSW.


5. Water Quality

5.1. WATER NUTRIENTS

5.1.1. Introduction

While all phytoplankton and algae require nutrients for their normal growth and reproduction,

increases in nutrient runoff can lead to eutrophication characterised by excessive algal and

phytoplankton growth. Blooms of blue green algae often occur in areas with excess nutrient load. In

addition, the relative abundance of different nutrients, and the chemical form in which nutrients occur

in a waterbody play an important role in determining the composition of algal and phytoplankton

assemblages (Harris 1999, Anderson et al. 2002). For example, ammonia is preferentially taken up by

small celled blue-green algae while nitrite is better utilised by green algae.

One of the main findings of the Blue-Green Algae Task Force (1992) which investigated the blue-

green algal bloom of the Darling River system in 1991, was that higher than normal concentrations of

water nutrients, particularly phosphorus, were responsible for creating conditions that favoured blue-

phosphorus may also be important in some cases (see review in Chapter 1).

The most important source of nutrients to coastal waters is catchment runoff, with most nutrients

delivered to waterbodies during rain events. On the east coast of Australia, rainfall is highly seasonal

and there is large interannual variability causing large variation in the timing and amount of nutrient

delivered to coastal waters. It is important to note that due to rapid uptake by algae and phytoplankton

(and efficient nutrient cycling between algae, sediments and the water column) nutrient concentrations

in the water column are often low, even when nutrient loads delivered to a waterbody may be high.

As is discussed in Chapter 2, Myall Lakes is at the end of the Myall River catchment, and has a very

low natural flushing rate. As a consequence, most of the nutrients that enter via rainfall events in the

Myall Catchment are processed in the lakes, as exports to the lower estuary are thought to be fairly

small. As with any lake, the concentration of nutrients present in the water at any point in time are a

consequence of the rate of delivery of nutrients and the rate of consumption and loss from the water

column. During sustained periods of dry weather, the concentration of nutrients in Myall Lakes is

determined by internal recycling and processing.



5.1.2 Methods

5.1.2.1 Rainfall

Daily rainfall records for Bulahdelah were obtained from Bureau of Meterology for the study period –

January 2000 – October 2002.

5.1.2.2 Water nutrient analyses.

Between January 2000 and October 2002, water nutrient concentrations were determined on 33

separate dates, usually for between 6 and 8 locations in the lakes. Between October 2001 and October

2002, 8 locations were sampled monthly, and a 6-week intensive phase of fortnightly sampling took

place from December 2001 to January 2002. The analytes tested for in each of the samples are

presented in Table 5.1.

Table 5.1. Analytes and detection limits for water nutrient analyses.

Analyte Method Used* Detection Limit

Total Nitrogen APHA 4500-NF&-PH 0.01 mg/L

Total Phosphorus APHA 4500-NF&-PH 0.002 mg/L

Nitrogen as Ammonia # APHA 4500-NH3 H 0.01 mg/L

Oxidised Nitrogen APHA 4500-NO3 I 0.01 mg/L

Soluble Reactive Phosphorus APHA 4500-PG 0.002 mg/L

Chlorophyll - ? + APHA 10200H 0.06 mg/m3

# While the laboratory reports Nitrogen as ammonia (NH3) in water samples, in natural waters where the pH is

less than 9, most ammonia exists as ammonium (NH4+). Therefore this report will report concentrations of

ammonium (NH4+).

* - Analyses performed by Australian Water Technologies, Sydney.

+ - As a means of assessing standing stock of phytoplankton and nutrient consumption.

Water samples were collected the top 2m of the water column using an intergrated pole sampler. Three

or four replicate samples from each site were combined in a clean, rinsed pail. Samples were

immediately extracted from this composite and chilled on ice prior to delivery to the laboratory. Prior



to filling, sample bottles were rinsed twice thoroughly with approximately 50 mL of sample to reduce

the risk of contamination.

Samples taken for Soluble Reactive Phosphorus (SRP),ammonuim (NH4+) and nitrate/nitrite (NOx)

were filtered immediately in the field using disposable 0.45 ? m filters and rinsed syringes. To reduce

the risk of contamination clean sample bottles were rinsed twice with 5 mL of filtrate before a 50 mL

sample was retained for analysis.

5.1.2.3. Near-Benthic Water collection.

In September 2002, water samples were collected from just above the sediment and from the surface.

Bottom water samples were collected by drawing a sample into a tube that was suspended 5-10 cm

above the lakebed. Sampling was conducted at 1 control site (Broadwater), and 2 experimental sites

(Upper Myall Rivermouth and Two-Mile Lake) in the deepest parts of the lake system. This was to

ensure that samples taken from the bed of the lake were least disturbed by wind-generated turbulence,

and most thus most likely to accumulate nutrients if benthic processes were releasing them from the

benthos.

The three replicate samples at each location were drawn to the surface and into a vacuum chamber

using a hand-operated vacuum pump. The samples were immediately filtered and chilled before

transportation to the laboratory. Positioning of the sampling tube above the lakebed was achieved with

the assistance of a closed-circuit underwater video on a boat over the sampling location. With the

video it was possible to clearly see the position of the uptake tube in relation to the benthos and avoid

contact with the sediment. In this way clean samples of the near-benthic water could reliably be taken.

Using the same method. three replicate surface samples were also taken at each location and treated in

the same manner as bottom water samples. Thus, the concentration near the lakebed could be

compared to the concentration of the remainder of the water column.

5.1.2.4. Interpreting nutrient data against ANZECC and ARMCANZ guidelines

The Agriculture and Resource Management Council of Australian and New Zealand (ARMCANZ)

National Water Quality Management Strategy (2000) sets out general annual guidelines for ambient

nutrient concentrations in freshwater, estuaries and marine systems (see Table 5.2). While there are

many steps to be undertaken in determining whether observed nutrient concentrations are higher than

is desirable for a given system (features specific to an individual waterway play a very significant

role), these values at least provide a framework for interpreting observed nutrient concentrations in a



broad sense. For this purpose alone, monthly average nutrient concentrations are compared to the

annual guideline figures in this chapter. Understanding the significance of these comparisons and

implications for lake health are discussed in Chapter 7.

TABLE 5.2: The Agriculture and Resource Management Council of Australian and New Zealand(ARMCANZ) National Water Quality Management Strategy (2000) guidelines for ambientnutrient concentrations.

Analyte Guideline Value Fresh Estuarine

Total Phosphorous 0.010 mg/L 0.030 mg/L

Soluble Reactive Phosphorous 0.005 mg/L

Total Nitrogen 0.350 mg/L 0.300 mg/L

Nitrogen as Ammonium (NH4) 0.010 mg/L 0.015 mg/L

Nitrogen as Oxidised Nitrogen (NOx) 0.010 mg/L 0.015 mg/L

Chlorophyll a 5 ?g/L 4 ?g/L

As mentioned above, two distinct periods average rainfall and lower than average rainfall, occurred

during the study period. Although the actual delivery of nutrients was not quantified during this

period, it is assumed that the two periods represent about average and then below average nutrient

loads to the system. The spatial distribution is thus discussed within the perspective of these two

regimes.

5.1.2.5. Data consolidation and presentation.

Interpreting the results of nutrient analyses from a large number of locations incorporating years of the

data is a cumbersome process. Although during the Coasts and Clean Seas Program the same 8 sites

were sampled on nearly all occasions, prior to this program samples were collected from many

different locations, at varying intervals. To avoid discarding valuable data that could otherwise be

included in the analysis, and to simplify this process, the data has been consolidated to 8 regions that

represent the main regions within the lake system. Table 5.3 outlines the area that corresponds to each

region.



Table 5.3. Location names for reporting Water Quality.

No. Name. Includes samples taken in these areas.

1 Rivermouth Upper Myall Rivermouth, western Broadwater.

2 South Broadwater Lower Myall Rivermouth, Mungo Brush, White

Tree Bay, southern Broadwater.

3 North Broadwater Mid-Broadwater, northern Broadwater

4 Bombah Point Bombah Point, Southern part of Two-Mile Lake.

5 Korsmans Landing Korsmans Landing, The Narrows, northern part

of Two-Mile Lake, Boolambayte Creek.

6 Violet Hill Boolambayte Lake, Violet Hill.

7 Myall Lake Myall Lake locations east of Burrah Burrah Pt.

8 Neranie Myall Lake locations west of Burrah Burrah Pt.

As well as this spatial consolidation, the results have been averaged temporally by the calender month

in which they were sampled. Much of the water quality is presented in maps which utilise this spatial

and temporal simplification to allow the presentation of a complex dataset in a visually simple manner.

It should be remembered however, that the maps are just intended as a visual aid to the interpretation

of the data and are not intended as a definitive guide to the exact concentration in locations that were

not sampled. However, in a well-mixed waterbody without many nutrient point-sources such as Myall

Lakes, it is likely the distribution of solutes within a region would be fairly uniform. The results

summarised in Figure 5.2 to Figure 5.13 show average monthly concentration of different types and

chemical forms of nutrients in Myall Lakes from April 1999 to October 2002. Colours were selected

to represent the relative concentration of each analyte throughout the lakes as well as how these relate

to the ARMCANZ guideline.

5.1.3. Results

The results of water column nutrient analysis from April 1999 to October 2002 are presented below in

graphical and map format. The role of wet and dry periods in influencing nutrient concentration is



highlighted and the results are compared to ANZECC and ARMCANZ guideline values for average

annual nutrient concentrations in fresh and estuarine waters.

Due to the large influence of rainfall on the export of nutrients from the catchment to waterway, the

results of nutrient sampling within Myall Lakes are presented in the context of the rainfall patterns

during the study.

5.1.3.1 Rainfall

During the study period two distinct rainfall regimes occurred. From March 2000 to July 2001,

generally close to average or above average rainfall was recorded (Figure 5.1). Although there were

months of low rainfall during this time, approximately 108% of the expected rainfall were received.

Drought conditions were experienced during the subsequent period of August 2001 to October 2002,.

Although 2 months of above average rainfall occurred, 7 consecutive months of below average rainfall

were recorded in this period with approximately 72% of the expected average rainfall in this period. It

is assumed that a higher nutrient load was being delivered to the lakes during the average rainfall

period than in the subsequent dry period

Figure 5.1. Monthly Rainfall at Bulahdelah. January 2000 to October 2002.

Because of the distinct differences in rainfall regime (and corresponding differences in water column

nutrient concentration) these two periods are dealt with separately in this chapter. The assumption is

that although flow in the Myall River was not measured, during the first period (average rainfall) a

Average and Recorded Monthly Rainfall - Bulahdelah

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greater nutrient load was being delivered to the lakes than in the subsequent (dry) period. This

assumption is also supported by the nutrient load investigations discussed in Chapter 3. This may

provide an opportunity to better understand the relative contribution of internal and external nutrient

loads in promoting and sustaining algal blooms.

5.1.3.2 Total Phosphorus (TP)

Monthly average concentrations of TP in the 8 regions of Myall Lakes are shown as maps in Figure

5.2 (average rainfall) and Figure 5.3 (low rainfall). There was a general pattern of higher values of TP

in the Rivermouth and Broadwater grading to lower values in Myall Lake. This pattern was apparent

in both average and low rainfall periods. During both the average and low rainfall periods, values of

TP at the Rivermouth and Broadwater sites were often above the ARMCANZ/ANZECC guideline

values of 0.01 mg/L (freshwater), and at times above 0.03 mg/L (estuarine) and reached 0.08 mg/L in

April 2000. In contrast, the Two-Mile, Boolambayte and Myall Lakes had average monthly

concentrations of less than 0.02 mg/L, for most months.

5.1.3.3 Soluble Reactive Phosphorus (SRP)

Average monthly SRP concentrations were often below detection limit (Figure 5.14) with the

exception of sites at the Rivermouth, Broadwater, and Mid-Lakes. At the Rivermouth site, SRP values

up to 0.16 mg/L were recorded on occasions throughout the study. In the Broadwater and Mid-Lakes

values were usually low, with elevated concentrations recorded in April 2000. SRP concentrations in

Myall Lake were below detection limit on all but one sampling occasion. Due to the large number of

occasions when values were below the analytical detection limit, these data have not been presented as

maps.



Figure 5.2: Average monthly concentration of Total Phosphorus in Myall Lakes during a periodof average rainfall April 1999 – July 2001.



Figure 5.3: Average monthly concentration of Total Phosphorus in Myall Lakes during a periodof low rainfall October 2001 – September 2002 .

5.1.3.4 Total Nitrogen (TN)

Average monthly TN values were higher than ANZECC/ARMCANZ guideline values throughout the

Lakes in both average and low rainfall periods. Highest values were recorded in Myall Lake at over

1.5 mg/L with average values of 0.7 mg/L during the low rainfall period. There was a general trend of

increasing TN values from the Rivermouth up to Myall Lake.



5.1.3.5 Ammonium (NH4+)

Average monthly NH4+ concentrations were highly variable among locations within Myall Lakes, and

over time (Figure 5.6, 5.7, 5.11 & 5.13). During the average rainfall period, values at the Rivermouth

and Broadwater, were usually low relative to Mid-Lakes and Myall Lake. However values exceeded

ANZECC/ARMCANZ guideline values on many occasions during both average and low rainfall

periods (Fig 5.16) and reached 0.24 mg/L in April 2000. During the average rainfall period, sites in the

Mid-Lakes and Myall Lake regions showed consistently elevated NH4+concentrations reaching

extreme values up to 0.9 mg/L. However, during the low rainfall period between October 2001 and

October 2002, values were generally below 0.05 mg/L and were usually lower than values recorded at

the Rivermouth and Broadwater.

It is clear that while the increase in ammonium concentration in March – April 2000 occurred at all

sites, the concentrations in the Broadwater declined to ‘normal’ concentrations by June 2000, while

locations in the Mid-Lakes and Myall Lake remained high or increased over the subsequent few

months. Across the lake system, the site at Violet Hill reported the highest concentrations, although

elevated concentrations were also found in Myall Lake (0.2 – 0.4 mg/L) in this period.

5.1.3.6 Nitrate/Nitrite (NOx)

NOx was sampled less intensively spatially and temporally in this period than other analytes. On one

occasion, very high concentrations were reported for the Broadwater (0.101 mg/L) but high

concentrations did not occur in other parts of the system (see Figure 5.8, 5.9 & 5.13). In general Myall

Lake had very consistently low concentrations, while other parts of the system varied considerably. In

the low rainfall period, concentrations greater than the ANZECC/ARMCANZ guideline value of 0.010

mg/L were recorded only in the upper Myall Rivermouth on 4 occasions, and at sites in the

Broadwater on 3 separate sampling days out of 17 (see Figure 5.13). For the rest of the lake

system NOx remained low, or below detection limit for the entire low rainfall period.

5.1.3.7 Chlorophyll a (chl a)

Most chlorophyll a samples were collected during the low rainfall period (see Figure 5.10). Except for

the Broadwater, chl a values were generally low and were below guideline values. In contrast, chl a

values at the Rivermouth site, were often above guideline values.

Locations that were known to possess high biovolumes of algae in the dry period (See Chapter 4), did

not show a correspondingly high Chlorophyll-? concentration at the same time. For example, Myall



Lake and Neranie which in December 2001 had average monthly biovolumes of 2.67 mm3/L for main

algal groups, had a similar concentration of Chlorophyll-? (2.63 ?g/L Chl.-? ) than the Broadwater

sites which had 0.212 mm3/L for the same groups (2.71 ?g/L Chl.-? ). This analyte is therefore not a

reliable measure of standing-stock for this system.

Figure 5.4 Average monthly concentration of Total Nitrogen in Myall Lakes during a period ofaverage rainfall April 1999 – July 2001.



Figure 5.5 Average monthly concentration of Total Nitrogen in Myall Lakes during a period oflow rainfall October 2001 – September 2002 .



Figure 5.6 Average monthly concentration of ammonium (NH4+) in Myall Lakes during a period

of average rainfall April 1999 – July 2001.



Figure 5.7 Average monthly concentration of N as NH4+ in Myall Lakes during a period of low

rainfall October 2001 – September 2002 .



Figure 5.8 Average monthly concentration of nitrate/nitrite (NOx) in Myall Lakes during aperiod of average rainfall April 1999 – July 2001.



Figure 5.9 Average monthly concentration of nitrate/nitrite (NOx) in Myall Lakes during aperiod of low rainfall October 2001 – September 2002.



Figure 5.10 Average monthly concentration of chlorophyll a (chla) in Myall Lakes fromSeptember 2000 – September 2002.



Mean (and Standard Error) ammonia concentrations.Drought period October 2001 - October 2002.

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g/L

)

Figure 5.11 Spatial distribution of average (with Standard Error) concentration of N asAmmonium in the low-rainfall period.



Figure 5.12. Total and soluble Phosphorus concentration in the four main regions of MyallLakes from April 2000 to October 2002.

River Mouth

TP

(mg/

L)

0.00

0.05

0.10

0.15

0.20

Broadwater

TP (

mg/

L)

0.00

0.05

0.10

0.15

0.20

Mid-Lakes

TP (

mg/

L)

0.00

0.05

0.10

0.15

0.20

Myall Lake

Apr-99 Ju

l-99Oct-9

9Jan

-00Ap

r-00 Jul-00

Oct-00

Jan-01

Apr-01 Ju

l-01Oct-0

1Jan

-02Ap

r-02 Jul-02

Oct-02

TP

(mg/

L)

0.00

0.05

0.10

0.15

0.20

River Mouth

SR

P (

mg/

L)

0.000

0.005

0.010

0.015

0.020

Broadwater

SR

P (

mg/

L)0.000

0.005

0.010

0.015

0.020

Mid-Lakes

SR

P (

mg/

L)

0.000

0.005

0.010

0.015

0.020

Myall Lake

Apr-99 Jul

-99Oct-9

9Jan

-00Ap

r-00 Jul-00

Oct-00

Jan-01

Apr-01 Jul

-01Oct-0

1Jan

-02Ap

r-02 Jul-02

Oct-02

SR

P (

mg/

L)

0.000

0.005

0.010

0.015

0.020



River Mouth

TN

(m

g/L)

0.0

0.5

1.0

1.5

2.0

Broadwater

TN

(m

g/L)

0.0

0.5

1.0

1.5

2.0

Mid-Lakes

TN

(mg/

L)

0.0

0.5

1.0

1.5

2.0

Myall Lake

Apr-9

9Ju

l-99Oct-9

9Jan

-00Ap

r-00

Jul-00

Oct-00

Jan-01

Apr-0

1Jul

-01Oct-0

1Jan

-02Ap

r-02

Jul-02

Oct-02

TN

(m

g/L)

0.0

0.5

1.0

1.5

2.0

River Mouth

NH

4+ (m

g/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Broadwater

NH

4+ (m

g/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Mid-LakesN

H4+ (m

g/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

Myall Lake

Apr-99 Jul

-99Oct-9

9Jan

-00Ap

r-00

Jul-00

Oct-00

Jan-01

Apr-0

1Jul-

01Oct-0

1Jan

-02Ap

r-02

Jul-02

Oct-02

NH

4+(m

g/L)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

River Mouth

NO

x (m

g/L)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Broadwater

NO

x (m

g/L)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Mid-Lakes

NO

x (m

g/L)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

Myall Lake

Apr-9

9Jul-

99Oct-9

9Jan

-00Ap

r-00

Jul-00

Oct-00

Jan-01

Apr-0

1Ju

l-01Oct-0

1Ja

n-02

Apr-0

2Ju

l-02Oct-0

2

NO

x (m

g/L)

0.00

0.02

0.04

0.06

0.08

0.10

0.12

FFigure 5.13. Concentrations of Total Nitrogen, NH4+, and NOx in the four main regions of Myall Lakes from August 1999 to October 2002.



5.1.2.8 Near-Benthic Water Collection

Figure 5.14 shows the concentrations of NH4+, NOx and SRP at bottom and surface waters at the

Rivermouth (A), Western Broadwater (B), and in Two Mile Lake (C). Water quality profiles showed

that the water column in the Western Broadwater was well mixed with only 6% difference in DO

saturation between surface and bottom waters. At this site there was little difference in nutrient

concentrations between the suface and bottom waters.

In contrast, water quality profiles at the Rivermouth and Two Mile Lake showed marked differences

between surface and bottom waters in concentrations of nutrients. At the Rivermouth, DO saturation

was only 3% at the bottom and 89% at the surface. At this site, NH4+ was more than 5 times higher in

bottom waters, in comparison to surface waters. SRP was also higher on the bottom than in surface

waters, although this was due to a single replicate having a high concentration (0.009 mg/L).

Differences were also noted at Two Mile Lake, but were smaller than at the Rivermouth. DO

saturation was 71% in bottom waters compared to 89% on the surface, NH4+ concentrations 3 times

higher on the bottom, but there was little difference in SRP concentrations.

Myall River Mouth, Sept. 24th, 2002.

0.008 0.010

0.0020.005 0.005

0.047

0.000

0.010

0.020

0.030

0.040

0.050

NH4+(Benthic)

NH4+(Surface)

NOx(Benthic)

NOx(Surface)

SRP(Benthic)

SRP(Surface)

Mea

n C

once

ntra

tion

(mg/

L)



Western Broadwater, Sept. 24th, 2002

0.0080.005

0.007 0.007

0.001 0.0010.000

0.010

0.020

0.030

0.040

0.050

NH4+ (Benthic) NH4+ (Surface) NOx (Benthic) NOx (Surface) SRP (Benthic) SRP (Surface)

Mea

n C

once

ntra

tion

(m

g/L

)

Two-Mile Lake, Sept. 24th, 2002

0.010 0.010

0.0050.001 0.001

0.033

0.000

0.010

0.020

0.030

0.040

0.050

NH4+(Benthic)

NH4+(Surface)

NOx(Benthic)

NOx(Surface)

SRP(Benthic)

SRP(Surface)

Mea

n C

once

ntra

tion

(m

g/L

)

Figure 5.14: Concentrations of NH4+, NOx and SRP at bottom and surface waters at theRivermouth (A), Western Broadwater (B), and in Two Mile Lake (C)

5.1.4. Discussion

5.1.4.1 Temporal and spatial patterns of nutrient distribution

The main source of nutrients to Myall Lakes is freshwater inflows that carry runoff from their

catchments. Inflows are highly seasonal depending on rainfall. Therefore, the type and amount of

nutrients exported from catchments, the location of riverine inflows, and the timing of rainfall events

will greatly influence the spatial and temporal distribution of nutrient loads to Myall Lakes. Nutrient

concentrations in the water column are a result of not only the nutrient load, but uptake by primary

producers, and biogeochemical processes in the water and sediment.



The gradient of phosphorus concentrations for both TP and SRP, from highest at the Myall

Rivermouth to lowest at Myall Lake, appears to reflect the nutrient load from the catchment associated

with freshwater inflow. Much of the Total Phosphorus loads in the waters entering the Broadwater are

likely to be bound to sediments that settle quickly to the bottom before they can reach Mid-Lakes and

Myall Lake. Dissolved phosphorus (SRP) is likely to be be taken up quickly by aquatic plants and

phytoplankton within the Broadwater before it can circulate further up the system. In contrast to

phosphorus, the concentration of total nitrogen is generally lowest at the Rivermouth site, and greatest

in Myall Lake. There are a number of potential reasons for this gradient. Much of the nitrogen may be

in the form of dissolved organic nitrogen (G. Harris pers comm) as a result of organic loading from a

largely forested catchment and long residence time. High TN values reflect large quantities of nitrogen

being cycled within the system (G. Coade pers comm). This is consistent with annual cycles of

growth and decay of large amounts of aquatic vegetation in Myall Lake and Mid-Lakes (Chapter 6).

The gradient may also reflect the importance of sediment biogeochemical processes in nitrogen

cycling, particularly the removal of nitrogen through denitrification. Differences in sediment between

the Broadwater and Myall Lake may greatly influence the rate of denitrification. In the Broadwater,

denitrification was measured on one occasion as good in the shallow sandy sediments, and relatively

low in the deep mud basin. Denitrification has not been measured in the Mid-Lakes and Myall Lake.

However, the benthos of these areas are covered in gyttja that is high in organic content and low in

oxygen. These are two factors known to inhibit the process of coupled nitrification-denitrification that

is so important in the removal of nitrogen from waterways.

These results highlight the difficulty of using nutrient concentrations as an indicator of nutrient status.

While TN is highest in Myall Lake and is often over the ANZECC/ARMCANZ guideline value, it is

likely that most of the nitrogen is in an organic form that is not bioavailable to phytoplankton and

algae.

It is clear that the concentration of all nutrients was lower and less variable during the low rainfall

period than during the period of average rainfall. This is particularly true of the reactive forms of N

and P (NOx, NH4 and SRP) which were present in very low concentrations during the low rainfall

period. In particular, the concentration of NH4+ was markedly lower during periods of low rainfall.

The elevated concentrations of NH4+ recorded at most sites in April 2000 occurred just after a period

of high rainfall in March 2000. At this time, 428 mm of rain fell in the catchment, which is

approximately 3 times the monthly average (159 mm). Although this suggests that runoff is a

significant source of NH4+ to Myall Lakes, it is likely that other mechanisms are involved given that

highest concentrations were recorded at sites remote from riverine inflows and elevated values were



not recorded from the Rivermouth site. In addition, the mechanism for the maintenance of high NH4+

concentrations in the months after the rainfall event is not known. NH4+ is usually taken up quickly by

phytoplankton and aquatic plants and is therefore usually in low concentration in coastal waters. One

explanation for high concentrations may be internal cycling of nutrients from the sediment to the water

column. Sampaklis (2003) found extremely high concentrations of NH4+ (up to 15mg/L) in the gyttja

overlying sediments in Mid-Lakes and Myall Lake. The gyttja is easily disturbed by wind mixing and

can increase NH4+ concentrations in the water column up to 10 times background levels during calm

weather. It is possible that disturbance of the gyttja at this time contributed to elevated concentrations

in the water column.

The influence of freshwater inflows on the delivery of SRP to Myall Lakes is demonstrated by the

consistently high values of SRP at the Rivermouth throughout the study, and the high values at sites

close to freshwater inflows (Broadwater and Mid-Lakes) after the large rainfall event in March 2000.

5.1.4.2 Near benthic water collection.

Higher concentrations of NH4+ and SRP in bottom waters were associated with reduced DO saturation.

These high levels may be due either to suboxic conditions near the sediment, stimulating the release of

NH4+ and SRP from the sediments, or to the build up of nutrients released from the sediment into

bottom waters that are not mixed into the water column. In either case, these results indicate that

sediment release of nutrients is an important process at sites in Myall Lakes. The even distribution of

nutrients through the water column at the Western Broadwater reflects the well mixed conditions at

the site.

Although this study did not attempt to quantify the loads of ammonium being delivered to the water

column, it is clear that the benthic material in the lakes is involved in the cycling and contribution of

nitrogen to the water column. The biological reduction processes that promote the incomplete

denitrification of nitrogen into ammonium operate in locations with excess organic carbon which has a

high biological oxygen demand. It is not surprising then, that low dissolved oxygen and elevated

ammonium were observed at the Myall Rivermouth site. However, it is particularly interesting to find

that the site in Two-Mile Lake which did not have low dissolved oxygen at the lakebed also had

elevated ammonium concentrations. This may be due to sediment characteristics and processes at this

site. As mentioned previously, the gyttja present in Two Mile Lake has high organic content, low

oxygen, and high ammonium content in pore waters. These characteristics suggest that coupled

nitrification-denitrification is likely to be low in these sediments due to inhibition of this process by

high organic load and low oxygen. Where organic matter is remineralised and denitrification is not



occurring, NH4+ is released from sediments. Low oxygen, either in waters near the bottom, or in the

gyttja, may also explain why NOx is not elevated at these sites where NH4+ was higher in bottom

waters. Under these conditions oxidation of NH4+ to NOx is inhibited.

5.2. NITROGEN STABLE ISOTOPE SIGNATURES OF AQUATIC PLANTS

5.2.1. Introduction

Stable isotope ratios of nitrogen have been used to quantify the degree and extent of impact from

anthropogenic nutrient inputs in rivers and coastal waters. The technique is based on the fact that

anthropogenic sources of nitrogen, have different ‘signatures’ or ratios of stable isotopes of nitrogen

compared to natural sources. Stable isotope analysis is a useful tool in identifying the location and

extent of specific impacts (Dennison and Abal, 1999), and the likely source of the nutrients. However,

it does not directly assess the impact of the nutrient load on the ecosystem, nor provide an assessment

of the environmental health of the study area.

The ratio of stable isotopes of nitrogen (N14 : N15) that occurs in the atmosphere is globally quite stable

(Lajtha and Michener, 1994). However, the ratio is able to be changed by any process, physical or

biochemical, that causes a change in the chemical form of the element. For example nitrification

(oxidation), denitrification (reduction), and nitrogen fixation, can lead to a change in the relative ratios

of the isotopes in the organisms that perform these functions, and ultimately in the ambient

environment.

Many of the processes associated with human activity (eg. application of nitrogenous fertilisers,

operation of sewage treatment plants, intensive animal agriculture) facilitate processes that change the

‘natural’ ratios of these isotopes, generally increasing the proportion of N15 (?N15). Increased

‘background’ ?N15 can provide a convenient method of tracing the presence of anthropogenic waste in

the environment. This method has proved to be particularly useful for tracing sewage being discharged

into an estuarine environment (eg. Dennison and Abal, 1999). Dennison and Abal (1999) found a clear

elevation of ?N15 in experimentally deployed algae in areas that receive the enriched effluent

compared to control locations, and decreasing ?N15 with increasing distance from the discharge point.

It was intended that a similar method might be used in Myall Lakes to identify whether a significant

proportion of the nitrogen fuelling plant growth in the lakes is arising from the catchment, or is being

recycled from the lakes.



Although human activity is known to increase the ?N15 in effluent arising from the sites mentioned

above, many other natural processes are also known to alter the atmospheric ratio of N14 to N15 which

make interpretation of ?N15 differences in the ambient environment difficult. For example the natural

range of soil ?N15 can vary from very depleted in N15 to highly enriched values, in the absence of any

sewage or other fertilisation (Lajtha and Michener, 1994). As a consequence, runoff leaving pristine

forested land without the addition of sewage effluent may be strongly enriched or depleted in N15 ,

making a positive N15 signal from a sewage treatment plant, for example, difficult to interpret at some

point downstream. This would be particularly so if the ?N15 signal in runoff from pristine land

changed through time, or if non-uniform rainfall initiates runoff from a variety of land-uses.

In the Myall Lakes catchment, pristine forest and a variety of land-uses (see Chapter 2) are present as

well as a STP at Bulahdelah. It is more than likely that the water entering Myall Lakes will have a

?N15 that varies through time depending on the amount of runoff or rainfall arising from different parts

of the catchment. Consequently, although this was not assessed in this study, it would be expected that

the water entering the system would have a highly variable and unknown ?N15. A preliminary survey

of ?N15 in vegetation in the catchment of the Upper Myall River in 2000, found that different

subcatchments did not demonstrate a clear pattern (DLWC, unpublished data).

Because of the complexity of the system and previous difficulties in interpreting Myall Catchment

?N15 data, a simple one-off study was conducted to examine patterns of spatial ?N15 distribution in a

single ubiquitous species of macrophyte in the lakes. This was intended to provide a starting point for

future studies, and allow some simple insight to nitrogen dynamics in the lakes.

The intention was to investigate whether plant growth in different parts of the lakes are utilising

different nitrogen sources, or whether the same nitrogen source is responsible across the system, at one

point in time. The Hypothesis being tested was ‘That there would be a significant difference in the

?N15 found in the tissues of the summer ephemeral Najas between any two locations’. The Null ‘That

no significant difference would be found’.

5.2.2. Methods

The macrophyte, Najas marina, was chosen as the subject for the stable isotope study. This

macrophyte grows abundantly in all the lakes of the system, although less so in the Broadwater (see

Chapter 6). It possesses roots that probably can extract nutrients from sediments, and leaves that may

absorb dissolved nutrients from the water. The plant is a summer ephemeral, and grows from seed to

mature flowering plants over each summer, and forms continuous dense beds over 1 kilometre in



length in Myall Lake. Following the summer bloom, the mature plants flower, produce seed, and then

die off gradually over winter (see Chapter 6). Consequently, it was possible to collect plants of similar

age and maturity from all locations in the lake, minimising any potential confounding created by

temporal differences.

On March 15th 2002, samples of Najas marina were collected from 8 locations representative of all

sections of the Myall Lakes system, except the upper Myall Rivermouth (Table 5.4). Within large

mono-specific macrophyte beds at each location several handfuls of plant were haphazardly gathered

from the topmost parts of the plants near the surface, and placed into a plastic bag that was then

sealed. Water depth at each location was approximately 3m.

Table 5.4 Sampling locations for Stable isotope study

Location Location name and description.

A Kataway Bay – Southern end of Eastern Myall Lake.

B Mayers Point – Northern part of Myall Lake.

C Mid-Myall Lake – Off Shelley’s Beach.

D Violet Hill – In eastern channel.

E Boolambayte Lake – Near Goat Island.

F Two – Mile Lake – Near Korsmans Landing.

G Bombah Point – Near Bombah Point ferry.

H Mungo Brush – Sand bar near White Tree Bay.

Samples were kept frozen prior to analysis. In the laboratory the leaves and terminal stems were

separated from the remainder of the plants (to ensure that material of approximately equal age was

tested) and a preliminary drying of material was conducted for 48 hours at 60?C. To test the precision

of the laboratory method, 8 replicate samples from each of the 8 locations were created. Dried plant

material was analysed by the School of Plant Biology at the University of Western Australia using a

standard in-house analytical method.



Results were analysed using a one way ANOVA to determine whether significant differences occurred

among sites, and Kruskal- Wallis test to identify which sites were different from each other.

5.2.3. Results

The mean values for ?N15 from N. marina tissue ranged from strongly negative values (-9) in Myall

Lake and Violet Hill, to slightly positive values (+3) in Two-Mile Lake and the Broadwater (Figure

5.15).

A one-way ANOVA on the effect of location on the mean for the ?N15 was highly significant,

(P<<0.001), so the null hypothesis was rejected.

A Kruskal-Wallis multiple comparison Z-Value test (regular test) in summary, showed that the mean

?N15 at Mayers Point, Myall Lake, and Violet Hill did not differ significantly (Group A in Figure

5.15), and the sites at Two-Mile Lake, Bombah Point and Mungo Brush were not statistically different

(Group B). The means of Kataway Bay and Boolambayte Lake did not differ from each other and did

not differ in some comparisons with sites in groups A and B.

-10.0

-5

0

+4.0

Kataw

ay

Mayers Pt

Myall L

.

Violet H

.

Boolam

bayte

Tw

o-Mile

Bom

bah Pt

Mungo B

r.

Myall Lakes delta N15 ‰– March 15th 2002

DeltaN15(‰)

Figure 5.15. Boxplots of N. marina tissue ?N15 recorded in the study (replicates = 8).

0

Group B

Group A



5.2.4. Discussion

The strongly negative ?N15 values recorded in Myall Lake and Mid-Lakes in this study were outside

the range usually reported for aquatic plants in coastal waters in the literature. Lajtha and Michener,

(1994) describe numerous mechanisms that can decrease the ?N15 values found in plant tissues and the

ambient environment. These include isotopic fractionation where ‘lighter’ forms of ammonia or nitrate

are selectively taken up by aquatic algae. This has been shown to produce strongly negative ?N15

values in the range –10‰ to - 20‰. Also the mobilisation (ie. movement through diffusion or

evaporation etc.) of ammonia can strongly favour the availability of lighter N14 isotope. This would

also contribute to negative ?N15 values in aquatic plants.

It is possible that the negative ?N15 values found in Myall Lake are due to one or both of these

mechanisms. Studies by Sampaklis (2003) have shown that the unconsolidated benthic sediments in

Myall Lake are easily disturbed which results in the release of high levels of NH4+ into the water

column. This would be readily available for uptake by macrophytes and may contribute to lower ?N15

values. In addition, strongly negative ?N15 values in dwarf mangroves in Belize was found to be due to

plant fractionation due to slow growth and low N demand associated with phosphorus limitation

(McKee et al 2002).

Variations in ?N15 must be examined in the context of natural variations due to genotype, and

environmental conditions. Although these factors can be responsible for local variability of 2-5 ‰

?N15 the observed range in Myall Lakes Najas of over 14 ‰ is unlikely to be due to within-species

variability. By sampling plants of the same species and age in similar habitats, any within-species

variability has been minimised and may reflect different nitrogen sources for plant growth in different

parts of the lakes.

5.3. PHYSICO-CHEMICAL PARAMETERS

5.3.1. Introduction.

The physico-chemical features of the water column, as well as nutrients, play a crucial role in the

development of blue-green algal blooms. In summary, the following water quality characteristics are

known to increase the likelihood of blue-green algal species becoming dominant:

1. Low salinity;

2. Warm water;



3. A change in the ambient turbidity; and

4. Stratification and or calm water conditions.

Low salinity is important as Anabaena and Microcystis are typically freshwater species and are

intolerant to increases in salinity (Chapter 4). The occurrence of stratification is a potentially important

feature in waterbodies that are prone to algal blooms. In short, the normal vertical mixing of the

waterbody is prevented by a much greater density of deeper waters over surface water. A number of

processes can be responsible for this discontinuity, but in shallow coastal lakes a layer of dense saline

oceanic water lying beneath fresher rain or catchment runoff water is one of the main processes that

causes stratification. The ability of some blue green species to regulate their buoyancy provides them

with an advantage over other species in turbid and/or stratified conditions. They are able to move

between well lit surface waters, and bottom waters where nutrients are available.

Subtle differences in water chemistry that can influence the health and diversity of the phytoplanktonic

community and macrophytes are also influenced by physico-chemical water quality. Variations in pH

for example, can affect the toxicity and speciation of chemicals in the water column. Reductions in

dissolved oxygen concentrations in bottom waters can enhance the release of stored nutrients (N and

P) into the water column which are then available for plant growth, and in extreme cases lead to fish

kills. Increases in turbidity decreases light penetration that may limit the production and distribution of

benthic plants and algae.

This chapter describes the physico-chemical characteristics of the water column of Myall Lakes during

the period April 1999 – October 2002.

5.3.2. Methods

Surface and bottom physico-chemical water quality measurements were made throughout Myall Lakes

from the Upper Myall Rivermouth to Neranie during the period April 1999 - September 2002. Water

quality measures generally coincided with algal sampling, and were not timed to capture specific

weather events. Water quality parameters of temperature, pH, DO and conductivity were measured in

the field using a water quality meter calibrated just prior to use. Generally data from between 6 and 8

locations for each sampling day were collected.

Light penetration through the water column was measured in different parts of the lake. Water clarity

was measured with a secchi disc during water quality and algal runs from September 2001 –

September 2002. On three occasions (February, June and September 2002), the instantaneous



measurement of Photosynthetically Active Radiation (PAR) attenuation through the water column was

measured at 0.5-1.0 m intervals with Li-Cor Underwater Quantum Sensors.

Longer-term measures of the amount of PAR underwater were collected using light loggers

(Dataflow) for the period December 2001 to February 2002 (2 sites) and again from June to August

2002 (4 sites). In each case the illumination was related as a percentage to logged ambient illumination

in air at Bombah Point. The loggers were deployed at the same depth in each location. Due to inflows,

the lakes’ depth changed during the study (thus changing the depth of the loggers) so these measures

are best considered as means of comparing the relative clarity of the water at different places in the

lake rather than the absolute intensity of PAR.

5.3.3. Results

Preliminary investigations showed that the physico-chemical character of 4 distinct regions could be

identified. As was the case previously above for the water nutrient data, samples have been averaged

where appropriate to typify the water value of each parameter. Sites in the following waterbodies have

been consolidated to create the graphs below:

1. Myall Rivermouth,

2. Bombah Broadwater,

3. Mid-Lakes (Two-Mile and Boolambayte Lakes),

4. Myall Lake (including Violet Hill and Neranie)

Temperature: The temperature of surface waters ranged between 10?C in winter and 27?C in summer

and was similar among the 4 regions. The only exception to this was the Myall Rivermouth in June

2002 which was approximately 3?C cooler than the main body of the lake (Figure 5.17).

pH: Few pH values were recorded prior to September 2001 but showed that values ranged between

6.7 – 8.2 with lower values at Myall Rivermouth and Myall Lake, and higher values at the Broadwater

and Two Mile Lake. After September 2001, values ranged between 6.2 and 9 with highest values in

Myall Lake followed by Two Mile Lake and Broadwater, and lower values in Myall Rivermouth. The

pH varied over this period with low values in November 2001 coinciding with a minor rainfall event.

There also appeared to be a seasonal trend with highest values in summer and lower values in spring

and autumn.



Dissolved Oxygen: Daytime DO ranged between 5-11 mg/L in the main body of the lake over the

period of the study. Values were similar among the 3 regions with slightly higher values at Myall Lake

compared to Broadwater and Two Mile Lake at times in late 2001 and 2002. Dissolved oxygen in the

Myall Rivermouth was generally lower than at other sites but varied substantially between sampling

times.

Conductivity: Conductivity ranged between 1-18 mS/cm. Values recorded between April 1999 and

September 2000 and between May and October 2001 were below 5 mS/cm at all sites in Myall Lakes

(Figure 5.16). At other times, the salinity regime was discretely different among the 4 regions. The

Broadwater and Two Mile Lake recorded highest salinity during dry periods due to saline intrusion

from the lower Myall River. Salinity in Myall Lake was low and relatively constant with a maximum

of 6 mS/cm reflecting the long distance from saline influence and absence of significant river input or

surface water flows. The upper Myall Rivermouth had low conductivity but values were highly

variable indicating the influence of both the saline intrusion during dry periods and river flows after

rainfall.

The conductivity of Myall Lake gradually increased between early 2001 to October 2002. Over the

study period Myall Lake did not display conductivities less than 2 mS/cm, which were found to be

necessary for the initiation of the Anabaena bloom of the Broadwater, and did not exceed 6 mS/cm

during dry weather. The large volume of water contained in this lake and small connection to the rest

of the system via the constricted passage at Violet Hill, means that rapid change in conductivity is

unlikely in this waterbody.

In contrast, the Broadwater displayed far more rapid and marked changes in conductivity (eg.

September – November 2000). As mentioned in Chapter 2, the Broadwater receives inputs of fresh

and saline estuarine waters and thus salinity is highly variable. The relatively small size and shallow

nature of the Broadwater means that the salinity responds quickly to inflows. The Mid Lakes (Two-

Mile and Boolambayte) are very small in volume compared to the other lakes. They receive direct

catchment runoff via Boolambayte Creek (as well as the lakes’ shoreline), and were found to be very

fresh for short periods (eg. September 2000) and were also at times similar in salinity to the

Broadwater(e.g. November 2001 to June 2002). It might be expected that because of the small size of

the catchment and volume of these lakes, the salinity in this part of the system is a more a reflection of

water movement from the Broadwater and Myall Lake. Strong currents (pers. obs) are often

encountered in dry weather at Violet Hill draining Myall Lake, and Bombah Point draining Two-Mile

Lake into the Broadwater. The presumed mechanism for this motion is seiching caused by wind-

generated water motion on Myall Lake creating localised lake-surface anomalies. In dry weather it



was common for there to be a gradient of increasing salinity further up the lake system, perhaps

demonstrating that this section of the lakes is a place of diffusion and mixing of water from the larger

waterbodies at opposite ends of Two-Mile and Boolambayte Lakes.



Figure 5.16 Electrical Conductivity of surface waters. April 1999 to Oct 2002.



Figure 5.16 (continued). Electrical Conductivity of surface waters. April 1999 to Oct 2002.



Figure 5.16 (continued) Electrical Conductivity of surface waters. April 1999 to Oct2002.



Figure 5.16 (continued) Electrical Conductivity of surface waters. April 1999 to Oct 2002.



Figure 5.17 Summary of physico-chemical water quality and rainfall for April 2000 toSeptember 2002.

pH

pH

5.56.06.57.07.58.08.59.09.5

Salinity

EC

(m

S/c

m)

02468

101214161820

Rainfall

Apr-99 Jul

-99Oct-9

9Jan

-00Ap

r-00 Jul-00

Oct-00

Jan-01

Apr-0

1Jul-

01Oct-0

1Jan

-02Ap

r-02 Jul-02

Oct-02

Rai

nfal

l (m

m)

0

50

100

150

200

250

300

Dissolved Oxygen

Dis

solv

ed O

xyge

n (m

g/L)

0

2

4

6

8

10

12

TemperatureT

empe

ratu

re (

o C)

81012141618202224262830

River Mouth Broadwater Mid-Lakes Myall Lake



5.3.3.1. Stratification

Significant differences in surface and bottom physico-chemical water quality (indicating stratification)

occurred infrequently during the study period, except in the Myall Rivermouth. This may be due to

mixing caused by horizontal wind-generated currents in the exposed and shallow waters of the lake

body. Figure 5.18 shows bottom and surface water values for temperature, salinity and dissolved

oxygen at the four main sampling regions. At the Myall Rivermouth site, there were differences in

surface and bottom temperature, salinity and dissolved oxygen on a number of sampling occasions. On

occasions when differences occurred, bottom waters were generally cooler, more saline (and thus

more dense) and as a consequence of the diminished vertical mixing, had lower dissolved oxygen than

the surface waters. The exception to this was in winter 2000 and 2002 when surface waters were

cooler than bottom waters, and in April 2000 and 2002 when dissolved oxygen was higher in bottom

than surface waters.

The Broadwater showed little evidence of stratification except in winter 2001 when bottom waters

were slightly more saline than surface waters. Slightly lower dissolved oxygen at the bottom was

recorded at the Broadwater and at Two Mile Lake in April to July 2001. The Myall Lake showed very

little difference in any parameter between surface and bottom waters on any sampling occasion during

the study.

On December 10th - 11th 2002, a wet weather event (~250 mm at Bulahdelah) sampled separately to

the C&CS program, created a freshwater layer in the Broadwater that remained intact for several days,

but did not cause anoxia in benthic waters.



Figure 5.18 Surface and bottom physico-chemical water quality between April 2000 and September 2002.

River Mouth

Tem

pera

ture

(o C)

8

1012

141618

2022

2426

2830

surface bottom

Broadwater

Tem

pera

ture

(o C)

8

1012

1416

182022

2426

2830

Two Mile

Tem

pera

ture

(o C)

8

1012

1416

182022

2426

2830

Myall Lake

Apr-9

9Jul

-99Oct-9

9Jan

-00Ap

r-00Jul-00

Oct-00Jan

-01Ap

r-01Jul-01

Oct-01Jan

-02Ap

r-02Jul-02

Oct-02

Tem

pera

ture

(o C)

8

1012

1416

1820

222426

2830

River Mouth

EC

(m

S/c

m)

02468

10121416182022

surface bottom

Broadwater

EC

(mS

/cm

)

02468

10121416182022

Two Mile Lake

EC

(mS

/cm

)

02468

10121416182022

Myall Lake

Apr-99Jul-

99Oct-9

9Jan

-00Ap

r-00Jul-00

Oct-00Jan

-01Ap

r-01Jul-01

Oct-01Jan

-02Ap

r-02Jul-02

Oct-02

EC

(m

S/c

m)

02468

10121416182022

River Mouth

Dis

solv

ed O

xyge

n (m

g/L)

0

2

4

6

8

10

12

surface bottom

Broadwater

Dis

solv

ed O

xyge

n (m

g/L)

0

2

4

6

8

10

12

Two Mile

Dis

solv

ed O

xyge

n (m

g/L)

0

2

4

6

8

10

12

Myall

Apr-99Jul

-99Oct-9

9Jan

-00Ap

r-00Jul-00

Oct-00Jan

-01Ap

r-01Jul

-01Oct-0

1Jan

-02Ap

r-02Jul-02

Oct-02

Dis

solv

ed O

xyge

n (m

g/L)

0

2

4

6

8

10

12


Department of Infrastructure, Planning and Natural Resources 112

5.3.3.2. Light availability

Secchi depth readings were made for the period August 2001 to July 2002 (Figure 5.19). The

Myall Rivermouth had the least light penetration indicated by low secchi depths (0.5-1.6m),

followed by the Broadwater. Two Mile Lake and Myall Lake had similar secchi depths with

greatest water clarity occurring in April and May 2002.

Instantaneous light attenuation through the water column was measured on three occasions

throughout the study and results are shown in Figure 5.19. There was a trend of decreasing

attenuation from the Rivermouth to sites in Myall Lake, as well as temporal differences. The

compensation depths (depth to which 1% of the incident light reaches) are shown in Figure

5.20. This depth is approximately the limit of photosynthetic production - where

photosynthesis of phytoplankton is equal to respiration rate and often indicates the depth limit

of seagrass and vegetation. The compensation depth ranged from around 2m at the

Rivermouth to around 8m at Myall Lakes indicating the potential for macrophyte growth on

the bed of different areas of the lake

Figure 5.21 shows the average daily records of incident Photosynthetically Active Radiation

(PAR) between 10 am and 2pm, and underwater at approximately 1m depth at a range of

sites, the percentage of incident PAR which reached approximately 1m depth, and the daily

rainfall at Bulahdelah. Because there was shading of subaquatic and ambient light loggers

when the sun was at low incident angles, only this period (when the sun was high overhead) is

used. Incident PAR varied according to cloud cover but generally reached 1600 – 1800

?mol/m2/s during the period December 2001 and March 2002. Values recorded during the

period showed lower levels in winter (1000 ? mol/m2/s – June 2002) increasing in Spring

(1400 ? mol/m2/s – September 2002).

The amount of PAR reaching a depth of approximately 1m varied widely among locations

within Myall Lakes and demonstrated the effect of rain events on water clarity and therefore

benthic illumination. In summer 2001 - 2002, water clarity was greater at Violet Hill

compared to Broadwater, with 2 - 2.5 times more PAR reaching the same depth at Violet Hill

than at the Broadwater. The reduction in water clarity in late January at both sites occurred

after a rain event. Water clarity gradually recovered over 6 weeks but took longer to recover

at the Broadwater than at Violet Hill.

In winter/spring 2002, water clarity was significantly higher at Myall Lake followed by Mid

Lakes, Broadwater and the upper Myall River mouth until mid July 2002. After July 2002

water clarity was higher in the Broadwater than Mid Lakes. Although the incident PAR



increased from July to September 2002, the amount of light at approximately 1m depth

steadily decreased at the latter 3 sites. This may have been related to small amounts of rainfall

in late July and August 2002.

Table 5.5 presents a summary of the logged data for winter 2002. Even in this period of below

average rainfall, there was a clear gradient of more light reaching 1m depth in Myall Lake

compared to the Broadwater. Within the Broadwater, at the Rivermouth site on average only

8.9% of incident light reached 1m depth compared Mid Broadwater (14.9%), indicating the

highly turbid nature of the Upper Myall River.

Table 5.5 Summary of logged PAR records.20 June 21 July 2002.

Location Name Mean percentage of

incident PAR at ~ 1m*

Myall Rivermouth (western Broadwater) 8.9

Middle Broadwater. 14.9

Two-Mile Lake (Korsmans Landing). 21.7

Myall Lake. 46.5

* - Depth was variable due to lake height fluctuations of +40cm.



secchi depth

Apr-9

9Ju

l-99

Oct-99

Jan-00

Apr-0

0Ju

l-00

Oct-00

Jan-01

Apr-01

Jul-0

1Oct-0

1Jan

-02Ap

r-02

Jul-02

Oct-02

dept

h (m

)

0

1

2

3

4

5River Mouth Broadwater Two Mile Myall

Figure 5.19 Secchi depths for 4 regions of Myall Lakes for the period August 2001 toSeptember 2002.

Light attenuation

Atte

nuat

ion

coef

ficie

nt (

k)

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2Feb 02 Jun 02 Sept 02

Compensation depth

RM SB NB BP KL VH ML

Com

pens

atio

n de

pth

(m)

0

2

4

6

8

Figure 5.20 Light attenuation and Compensation depth for sites within Myall Lakes forPeriod Feb – September 2002. RM = Rivermouth, SB = Southern Broadwater, NB =

Northern Broadwater, BP = Bombah Pt, KL = Korsmans Landing, VH = Violet Hill, ML =Myall Lake.

RM SB NB BP KL VH ML



Figure 5.21 Average daily PAR intensity (between 10am and 2pm) at 1m depth andrainfall at Bulahdelah.

PA

R (

umol

/m2 /s

)

0

200

400

600

800

BroadwaterViolet Hill

% P

AR

at 1

m

0

20

40

60

80

100

Dec 01 Jan 02 Feb 02 Mar 02

Rai

nfal

l (m

m)

0

20

40

60

80

100

120

RivermouthBroadwater Two Mile LakeMyall Lake

Jun-02 Jul-02 Aug-02 Sep-02

AirP

AR

(um

ol/m

2 /s)

0

200

400

600

800

1000

1200

1400

1600

1800

2000



5.3.4. Discussion – Physico-chemical water quality.

Surface water quality values recorded in Myall Lakes generally fell within normal ranges for

coastal and freshwaters (ANZECC and ARMCANZ 2000). Exceptions were slightly elevated

levels of pH in Myall Lake after September 2001 that may be due either to high productivity

of macrophytes or sulphur reduction in benthic sediments. Low dissolved oxygen on

occasions in the Rivermouth may be due to high organic loading.

Spatial differences were observed among the four regions in the degree of stratification, water

quality parameters, and water clarity. These differences reflect the relative influence of

rainfall and catchment inputs, and physical and ecological processes among the regions.

The Upper Myall Rivermouth was characterised by frequent differences between surface and

bottom temperature, salinity and DO. As well, this location had low and variable salinity,

acidic pH and low DO. Low water clarity was also found here and nearby in the western

Broadwater. This site is most influenced by rainfall and runoff from the catchment. The

observed acidic pH may result from tannic acids in the river which is typical of low-gradient

coastal rivers in Australia. Low DO is likely to be a result of high biological oxygen demand

in waters from the catchment combined with a small surface area over which oxygen from the

atmosphere can diffuse. The lower water temperatures at this location may play a role in

preventing blue-green algae blooming in this location (Chapter 4).

The Broadwater and Mid Lakes are similar in that they are normally brackish although the

salinity is somewhat variable and pH and DO values were within normal ranges. There was

reduced DO near the benthos in the Broadwater on some occasions which may be due to high

rates of sediment remineralisation and organic decomposition of material transported from the

catchment in the river. It is likely that fine particles and organic matter settle to the bottom

quickly once the flow is reduced as it reaches the Broadwater. The lower water clarity in the

Broadwater compared to the Mid-Lakes is also likely to result from the abundance of fine

particles at this site which are easily resuspended in an area open to the wind. The bathometry

and sediment composition of the Mid-Lakes region makes it less susceptible to resuspension.

Myall Lake is least influenced by rainfall and catchment influences due to its distance from

major inflows. Stratification was not observed during this study. This region has low and

stable salinity, sometimes elevated pH, normal levels of DO and high water clarity. Myall

Lake is a large open area with a depth of not more than 5 m that would experience substantial

wind mixing reducing the likelihood of stratification. The elevated pH may be due to either to

sulphur reduction in sediments or high production by ephemeral macrophyte species that

reach a high biomass in this region in late spring and summer each year.



Calculation of compensation depth shows that areas closest to river inputs (upper Myall

Rivermouth and Broadwater) which are most susceptible to reduced water clarity have the

shallowest compensation depth. This means that any decrease in water clarity in these areas

due to increased turbidity in river inputs may decrease the depth to which aquatic plants are

able to grow. Depending on the bathometry of the region, this may substantially reduce the

area available for plant growth. Macrophyte beds are an important part of the ecology of

Myall Lakes as they provide food and shelter for many species of birds and fish, stabilise

sediment, and play an important role in taking up and regulating nutrients in the water

column.

Of the physico-chemical water quality data presented here the finding that low (and

potentially) rapidly-changing conductivity, and low water clarity occur in the Broadwater is

of great significance for the development of scum-forming blue-green algal blooms in the

lakes. The coincidence of these two factors (as mentioned in Chapter 4) create a regime that

favours fresh-water algal species that can regulate their buoyancy. These are characteristics of

Anabaena, which was a primary coloniser during the 1999 bloom. It is thus no coincidence

that although the toxin-producing cells were found in the mid-lakes later, they occurred in

greatest abundance on the Broadwater. The upper Myall Rivermouth, which is the source of

nutrients and turbid water, is cooler than the Broadwater and this may influence the growth of

slower-growing blue-green algal cells. Further research would be required to confirm this

however.

The salinity regime and clear waters of Myall Lake also seems to discourage the growth of

scum-forming blue-green algae. Because this lake has no large freshwater catchment inputs,

runoff entering via the Myall River and Boolambayte Creek displaces water already resident

in the Braodwater and Mid Lakes, pushing it up into Myall Lake (pers obs – December 2002).

This mechanism appears to prevent fresh and turbid water reaching the upper parts of the

system and thus may prevent Myall Lake from providing the conditions necessary for the

scum-forming blue-green algal blooms that dominated the Broadwater in 1999-2000. The

death of phytoplankton competitors (that would otherwise out complete blue-green algae) due

to rapidly declining salinity and high turbidity following a large rain event could be a means

by which blue-green algae were able to dominate in the Broadwater (Chapter 4). The high

water clarity, stable conductivity, as well as instances of high levels of Ammonium, may

explain the dominance of the smaller-celled blue green algae (eg. Chroococcus) in Myall

Lake. As discussed in Chapter 4, these species can not control their buoyancy (thus require

good clarity and well mixed water) and are Ammonia scavengers.



So although the low-flushing of the lakes means that the system is a sink for nutrients, this

feature also means that there is a limited ingress of runoff into the upper parts of the lakes,

which seems to buffer the areas with the least water exchange ( ie. Myall Lake) from the

effects of catchment degradation (which mainly influence the Broadwater). Although it has

not been quantified it seems likely from conductivity and water nutrient results that there is a

differential impact from catchment inputs on each lake of the Myall Lakes system. The

Broadwater, which takes high nutrient runoff directly from the Myall River, undoubtedly is

receiving a far greater nutrient load than Myall Lake which appears to mainly receive water

that has been displaced from other parts of the lake system, which has had most available

nutrients removed previously. This feature has meant that very little catchment-derived silt

has accumulated on the bed of Myall Lake, and a unique benthic flora has developed instead

(see Chapter 6). Also, it has led to a situation of phosphorous limitation in Myall Lake,

making it particularly sensitive to any changes in the amount of this nutrient that it receives.

Chapter6, Aquatic vegetation and lake habitat. Understanding Blue Green Algae Blooms in Myall Lakes NSW.


6. Aquatic vegetation and lake habitat

6.1. BACKGROUND

6.1.1. Vegetation

Macrophytes are an important component of both estuarine (Allanson and Baird, 1999) and

freshwater (Sainty and Jacobs, 1994) ecosystems. They play a number of important roles

including primary production, providing habitat and food for fauna, promoting denitrification

by aerating sediments, and reducing the resuspension of sediments (Allanson and Baird,

1999). Macrophytes are good indicators of aquatic ecosystem health as they are especially

vulnerable to decline and changes in species composition in response to eutrophication and

sedimentation.

Pristine waterways are commonly characterised by long-lived macrophytes, predominantly

perennial angiosperms, although some are naturally dominated by short-lived species. For

example, seagrasses are considered an indicator of good health in NSW estuaries while the

growth of extensive beds of filamentous algae is considered a sign of poor health (Astill and

Lavery, 2001). Macrophytes, like terrestrial plants, are reliant on light in the wavelengths of

400-700nm, or Photosynthetically Active Radiation (PAR), to supply their energetic needs. In

water, PAR declines sharply with depth, restricting plant growth to the well-illuminated areas.

As a consequence, the total area that is suitable for the growth of macrophytes in a given

waterbody varies depending on the clarity of the water, and the area of the lakebed that falls

within the illuminated zone. This means that areas which appear to be ideal plant habitat

might not support macrophytes because water clarity is poor, or the bed is too deep.

As well as the physical characteristics of waterways influencing bed illumination, over the

course of a year, the area of lakebed that receives enough light to support perennial plants in a

particular lake will vary considerably. Incident Photosynthetically Active Radiation (PAR) at

noon in summer is nearly three times that of mid-winter (DLWC, unpublished data). If the

water clarity remains constant throughout the year, more light will reach the lake bed in

summer than winter.

One of the possible consequences of a large seasonal change in light penetration is seasonal

changes in the distribution or density of macrophytes. A similar change in macrophyte

communities can also be expected in response to increasing turbidity (Livingston, 2001). For

this reason, the decline of perennial plants in deeper areas of lakes can be an early warning of

deteriorating water clarity. Ephemeral species that are more suited to carrying out their entire

life-cycle during the summer months may then become more abundant, under some



circumstances, leaving bare sediment in winter when light levels are too low for plant growth.

However, the establishment of ephemeral species (eg Najas), as opposed to perennial species,

may also be influenced by the substrate type.

Numerous studies in Australia have indeed found that in waterways that have increasing

nutrient loads and declining water clarity, there is a shift in macrophyte assemblages to

species with short-lived life histories (Lavery, Lukatelich and McComb, 1991) and often a

retraction of long-lived species to shallower areas due to better light availability. While the

predominance of short-lived plants can be a key to understanding the ecological processes

operating in a waterway, naturally high variability in community composition in healthy

waterways can confuse interpretation.

Changes in the abundance, distribution and diversity of macrophyte assemblages in a

waterbody are a natural component of a normal functioning ecosystem (Allanson and Baird,

1999). Within a macrophyte bed it would be expected that individual plants that are

recruiting, maturing, and plants that are dying would be present. As well, changes in the

dominant taxa may be due to other ecological processes such as grazing or competition, or in

response to long term changes in water quality. Therefore, it is essential to sample through

time to monitor the changing composition of macrophyte beds. The main objective of this

component of the study was to provide a qualitative description of the changes in the types of

plants observed in the lakes over a 12 month period, that would provide information on the

biological characteristics of Myall Lakes and provide an indication of the likely health of this

system and a guide to where further investigation should be undertaken.

6.1.2. Lakebed sediments.

The bed of lakes and estuaries are sinks for sediment, nutrients and organic matter. However,

these nutrients are not usually available for algal growth as they are tightly bound to silt

particles, or are contained in decomposing organic matter. Therefore, most of the nutrients

entering the lake from riverine inputs are retained in the sediments and removed from the

water column for an indefinite period. Phosphorus in particular can be removed from aquatic

ecosystems in this way.

As well as capturing nutrients, sediments are able to process and remove nitrogen through

bio-geochemical processes. Microbial processes convert nitrogen in organic matter to the gas

phase (N2) that is then diffused to the atmosphere and removed from the system. While this

process of denitrification has the potential to cleanse lakes of nitrogen, the presence of

excessive amounts of organic carbon in the sediment leads to a decline in the rate of the

preceding step of nitrification (Waite, 1984). This can result in the release of dissolved



inorganic nitrogen (DIN) which can be readily taken up by algae. The actual rate of

denitrification or DIN release is dependant on a variety of factors including grainsize,

microbial assemblage present, dissolved oxygen levels, and organic content. All these factors

interact in complex ways. Therefore, rates of denitrification and DIN release cannot be

predicted from sediment nutrient concentration alone.

So while the presence of high amounts of nutrients and organic matter in material on the

lakebed need not necessarily be cause for concern, these patterns could provide some insight

to the interactions occurring between the water column and lakebed. To characterise the types

of material present on the bed of the lakes and provide a starting point for further

investigations into lakebed processes, a one-off lake wide survey was made in this program.

With the use of data kindly provided by Geosciences Australia, who surveyed the Broadwater

in 2000, a more complete picture of benthic character was made.

As well as this lake-wide survey in late 2001 it was noted that an unusual benthic microbial

assemblage was present in shallow areas, which seemed to dominate the benthos in Two-

Mile, Boolambayte, and Myall Lakes. Some preliminary investigations into the identity and

features of this microbial assemblage were made and are reported also.

6.2. METHODS

6.2.1. Vegetation assessment method.

A preliminary survey was conducted in September 2001, where the major types of

macrophyte were collected and subsequently identified by the National Herbarium. In

November 2001, February 2002, June 2002, and September 2002 qualitative assessments

were made of the distribution of the main vegetation taxa identified.

Three methods were used to identify the main types of vegetation:

1. Visual survey. In shallow water it was possible from a boat to see and rapidly identify the

macrophytes present.

2. Rake collection. Using a tethered metal rake it was possible to gather and identify loosely

rooted vegetation. The rake was thrown and dragged towards the boat several times at

each location to ensure a representative sample was collected.

3. Sled-mounted underwater video. Areas with hard-packed sand and strongly rooted

macrophytes were not well collected with the rake and were assessed using a closed-

circuit underwater video. The general method involved deploying the sled from a boat in



deep water and towing the equipment slowly towards the shore. Transects were observed

on the monitor from the boat and taped for later analysis if required.

The general method used at each location was to perform visual surveys in shallow parts of

the area, and these were combined with transects from or towards the shore, in which the

presence of each taxa found at each 0.5m depth increment was recorded (eg. At 1m, 1.5m,

2.0m et c.). The depths were noted from an on-board depth sounder and later corrected for

variation in lake height by recording the reading at a height board at Mayers Point.

In each method a Global Positioning System (GPS) was used to record points at which

samples were taken, and in the case of the video, where a change in the benthic macrophytes

was found. In this way points were directly transferable to the Geographic Information

System GIS), which were used in the creation of the maps that follow. The distribution of

each taxa at each sampling occasion was made into a GIS shapefile for use in later

applications.

6.2.2. Lakebed assessment method.

The general method of benthos sampling was as follows:

Fifty-one locations were selected to form a rough grid pattern and the positions recorded on a

GPS. To collect material, 40 cm long, 8.5 cm diameter transparent polycarbonate cylinders

were used in a hand-operated coring device. At each location 6 replicate core samples were

taken. Care was taken to ensure undisturbed cores were collected, and that the surface/water

interface was intact. The samples were immediately sub-sampled to collect the top 2 cm of

each core. The 6 replicates were combined to form a composite sample. Samples were kept

cool and transported to the laboratory. In the laboratory, the composite from each site was

passed through a 2 mm sieve which removed seeds and recently deposited vegetation. A small

sample was mounted and examined qualitatively to check for the presence of benthic

microcystis under compound microscope. The sample was thoroughly homogenised and sub-

samples were taken which were then dispatched for analysis.

Analysis of sediment nutrient content was performed by AGAL (a NATA accredited

laboratory) and grainsize analysis was performed without charge by Geosciences Australia. A

summary of the analyses performed is presented in Table 6.1, below. All samples were

analysed for Total Organic Carbon (TOC), but approximately half of the samples were

analysed for nutrients to reduce the total cost of the analyses.



Although Total Nitrogen (TN) analysis was performed for only approximately half of the

locations, preliminary analysis found a high correlation between TOC and TN for benthic

material throughout the lake system. To extrapolate the relationship to locations that did not

have samples analysed for TN a second order polynomial equation (R2 = 0.9558) was fitted to

the data, and values for TN at other locations were calculated. Low correlations between TOC

and, Total Phosphorus (TP) and Total Sulphur (TS) were found which precluded performing

this extrapolation on these analytes.

Table 6.1. Number of samples analysed in each region of Myall Lakes.

Number of samples - AnalytesRegion

TOC TN TP TS Grainsize

Myall Lake 28 12 12 12 28+

Mid Lakes 20 8 8 8 20+

Broadwater * 21* 21* 21* 21* 21*

Myall River and Nerong Creek 6 6 6 6 6+

* - Data from 2000, provided by Geosciences Australia+ - Analysis provided by Geosciences Australia, 2002. Data not presented.

6.3. RESULTS.

6.3.1. Vegetation

Figure 6.1 to Figure 6.9 present a summary of each survey’s findings. The maps are intended

as a guide to the approximate distribution of each taxa based on:

1. The depth to which each type of plant was observed in each location,

2. The known depth contours which were mapped by DIPNR in 2002.

As mentioned, the maps are generalisations about the distributions of macrophytes, but are a

good indication of the different characters of different locations.

Taxa that occurred in discrete beds (the large macrophytes), were quite easily mapped by the

method described above, while the algae and ephemeral plants presented a more challenging

scenario. The distribution of many of these (especially Chara spp. and Nitella spp.) were

more or less ubiquitous throughout the lakes, occurring in low density in most shallow

locations. While the maps presented are intended to show a presence/absence of each type of

macrophyte, the distribution of the charophytes is restricted to locations where these taxa



formed a substantial component of the benthic flora. While this was not formally quantified in

the field, the presence of charophytes was not plotted unless they composed at least

approximately 5% of the total cover, estimated in the field visually.

6.3.2. Types of aquatic plants found in Myall Lakes

Table 6.2 presents a summary of the characteristics of the dominant taxa in Myall Lakes that

are presented in the maps.

Table 6.2. Summary of dominant plants found in Myall Lakes.

Taxon Life-strategy - Type Notes on OccurrenceVallisneria gigantea Perennial -

AngiospermExperienced winter die-back in the Broadwater instudy period. Confined to shallow areas ofBroadwater and Two-Mile lake and fringes of otherareas.

Ruppia megacarpa Perennial -Angiosperm

Confined to shallow areas of Broadwater and Two-Mile lake and fringes of other areas. Noted to beundergoing significant recruitment in deeper areas ofBroadwater in study period.

Potamogeton perfoliatus Perennial -Angiosperm

Although not found in 2001, this taxa recruited andcolonised bare shallow areas in early 2002, andbecame quite abundant by late 2002 especially in theBroadwater.

Myriophyllumsalsugineum

Perennial -Angiosperm

Present in all lakes except the Broadwater. Did notappear to change distribution in study period.

Najas marina Annual - Angiosperm Underwent great increase in biomass and distributionin all lakes except Broadwater over summer, andsuffered dramatic die-back over winter.

Charophytes? Eg. Nitella hyalina

and others.? Chara spp.

Ephemeral - greenalgae

Present all year in all lakes, but in far greaterabundance in summer in Myall Lake.

Macroalgal Assemblage? Filamentous green.

Ephemeral – variousalgae.

Present only in Broadwater on otherwise baresediment and in conjunction with macrophytes in thislake. Distribution did not appear to change over thestudy period.



Figure 6.1. Spring macrophyte distribution in the Broadwater.

Figure 6.2. Summer macrophyte distribution in the Broadwater.



Figure 6.3. Autumn macrophyte distribution in the Broadwater.

Figure 6.4. Winter macrophyte distribution in the Broadwater.



Figure 6.5. Spring macrophyte distribution in the Mid-Lakes.

Figure 6.6. Summer macrophyte distribution in the Mid-Lakes.



Figure 6.7. Autumn macrophyte distribution in the Mid-Lakes.

Figure 6.8. Winter macrophyte distribution in the Mid-Lakes.



Figure 6.9. Spring macrophyte distribution in Myall Lake.

Figure 6.10. Summer macrophyte distribution in Myall Lake.



Figure 6.11. Autumn macrophyte distribution in Myall Lake.

Figure 6.12. Winter macrophyte distribution in Myall Lake.



6.3.3. Spatial Distribution of plants in Myall Lakes.

Broadwater - Perennials.

In the Broadwater large areas of perennial macrophytes (V. gigantea to approximately 1.0m,

and R. megacarpa to approximately 1.5m depth) occur on the sandy benches on the northern

and south eastern shores. While a few individuals may be found in deeper water the steep

drop-off found near the channel areas restrict the distribution of these taxa. Deeper areas of

the R. megacarpa beds contained mainly immature plants which formed a dense turf.

In the western Broadwater the distribution of V. gigantea is further limited to approximately

0.8m, presumably because of the low light penetration in this area (see Chapter 5) and forms a

narrow band along the shore. Similarly, R. megacarpa in this area is found to only

approximately 1.0 m depth, and is restricted to the shore line areas, with a sparse small bed

being found on the bar south of the entrance of the upper Myall River. P. perfoliatus was

found to grow in similar locations to the other two species, but was found to depths of

approximately 2.0m.

Broadwater - Ephemerals.

Large areas of assemblages of filamentous green macroalgae were present on all sampling

occasions on the northern, eastern, and southern shores of the Broadwater. These were

composed of a variety of estuarine and marine genera mainly Gracillaria, Enteromorpha, and

others. These assemblages occurred mainly in conjunction with R. megacarpa beds, but were

also found to occupy bare sediment in some areas. The macroalgal assemblage was observed

to be present to approximately 2.0 m depth in some locations, and formed a dense mat on the

northern Broadwater shallows approximately 2 km in length.

Much of the sediment mapped as being ostensibly bare in the Broadwater, did support low

densities of charophytes on all occasions although these did not form dense beds as were

found elsewhere in the system. Stunted charophytes (~5 cm in height) were observed growing

in depths to approximately 2.5 m, in some locations.

Mid-Lakes – Perennials

The sand bars of Two-Mile Lake and Korsmans Landing, have a similar macrophyte

community composition to the bars of the Broadwater, with the addition of Myriophyllum

salsugineum which grows in conjunction with the other taxa. Stable beds of V. gigantea and



R. megacarpa are present all year to a depth of approximately 1.5m. However apart from this

southern portion of Two-Mile lake, and east of the mouth of Boolambayte Creek, there are no

large beds of perennial macrophytes in the mid-lakes. Although Boolambayte Lake does

contain the same macrophyte taxa as Two-Mile Lake these plants are not present other than as

narrow beds along the shore and around Goat and Sheep Islands.

Some of the cause of the lack of perennial macrophytes might be attributed to the steep bed

edges in ‘The Narrows’ of northern Two-Mile Lake, which does not contain shallow areas

that might support macrophyte communities. However, Boolambayte Lake which does have

large areas of shallow bed that might be expected to hold perennial macrophytes is also

without large beds, so presumably the absence of perennial plants is due to some other factor.

Mid-Lakes – Ephemerals / Annuals

During summer the mid lakes support an abundance of charophytes and N. marina which

occupy all parts of these lakes to approximately 3.5 m depth. Even the deepest parts of

Boolambayte Lake are thus able to support these plants, which form very dense beds which

reach the water’s surface in many locations. Two-Mile lake also was found to support large

areas of N. marina, but did not contain beds of charophytes as extensive as those found in

Boolambayte Lake.

Myall Lake – Perennials

Myall Lake does not contain any substantial areas of perennial macrophytes, although nearly

all the rocky fringing shoreline areas do support a narrow band of V. gigantea, R. megacarpa,

and M. salsugineum, on the northern and southern shores. Although a formal assessment of

plant health was not undertaken, during the study period the macrophytes appeared to be

healthy (not fouled with epiphytes) and produced flowers (V. gigantea in summer, M.

salsugineum in winter). No noticeable change in the density or depth to which the plants were

growing was seen during the study period.

Myall Lake – Ephemerals / Annuals

As was found for the Mid-Lakes, almost the entire bed of Myall Lake is shallow enough to

allow the growth of charophytes and N. marina for some of the year. Consequently, at the

peak of the growing season dense shoals of these plants were found in most parts of the lake.

In places that were less than 3 m deep N. marina was observed forming mono-specific shoals

over 2 km long that reached the surface of the lake. There did not appear to be any spatial

differences in the abundance of these plants within Myall Lake other than a low abundance of



these taxa in shallow sandy areas, which contained small scattered plants. The sandy areas of

western Myall Lake (Neranie Sands) and the south western corner (Palmers Bay) did not

support extensive beds of these plants, and were mainly bare sediment on all sampling

occasions.

6.3.4. Temporal Change in the Distribution of plants in Myall Lakes.

A number of changes in the abundance and distribution of macrophytes in the lakes were

observed in the study period. Table 6.3 summarises the changes through time within the study

period of the area covered by each taxa.

Table 6.3. Summary of extent of cover of each taxa.

Approximate Total Area of each Taxon in Myall Lakes.(Hectares)Taxa

SpringNov. 2001

SummerFeb. 2002

AutumnJune 2002

WinterSept. 2002

V. gigantea 377 377 377 377R. megacarpa 710 710 710 710

M. salsugineum 140 140 140 140P. perfoliatus 0 191 382 568Charophytes 2310 4159 4159 2186N. marina 1412 5443 5443 526

Macroalgal Assemblage 210 210 210 210

6.3.4.1. Najas marina and Charophytes – Annual growth cycles

The most obvious changes over the 4 surveys is the large annual change in area covered by N.

marina, which underwent a large summer bloom and winter die-back in all areas except for

the Broadwater. This species was observed to grow vigorously from seed (presumably) in

early spring to mature plants in summer, which then broke up and decayed over winter. Much

of the areas formerly occupied by living Najas was found to contain decaying fragments in

Autumn 2002. Drifting fragments containing seeds is a mechanism by which this species is

distributed (Sainty & Jacobs, 1994). Sediment samples taken from most areas of Myall Lakes

in September 2002 often contained large numbers of seeds.

Although plants over 4 m in length were found in the lakes, the roots system of this species

consists of relatively short (~40 cm) simple roots that arise from a creeping underwater stem,

and is densely covered with short (<10 mm) fine hairs. It would appear that this species is

able to extract nutrients from the benthos, but may also be reliant on absorbing water borne

nutrients through its leaves like many aquatic plants (Sainty & Jacobs, 1994).

In conjunction with the summer growth of Najas, Charophytes also underwent a large

summer increase in area covered by living plants, and winter die-back in the study period. An



increase of approximately double the area occupied in winter was observed, with roughly 4,

100 hectares of lakebed containing these plants in summer.

All lakes of the system except the Broadwater supported a summer bloom of these taxa.

Although individual Najas plants were found scattered in many locations in the Broadwater,

only a small area demonstrated a significant abundance of these in summer. In parts of the

Broadwater small charophytes were found to be fairly abundant as small clumps, but not in

large monospecific stands that were observed elsewhere.

6.3.4.2. Vallisneria gigantea – Broadwater die-off

Although a detailed assessment of the standing stock and productivity of this taxa was not

performed there seemed to be a significant die-off of adult plants in the winter of 2002 in the

Broadwater. Other areas did not appear to be affected. Overall, the areal distribution of plants

did not change appreciably following the decline, but a noticeable thinning of the beds was

found in the September 2002 survey, which followed the die-off. The northern shore and

shoal to the north of the Lower Myall River entrance was observed to contain virtually no

mature plants, in the winter of 2002. Large numbers of small V. gigantea were found in these

locations that lost adult plants, so this decline did not cause a complete loss of this taxa from

these areas.

Curiously, locations elsewhere that contained this taxa did not display a loss of adult plants. A

dense bed near the entrance of the Upper Myall River was found to contain both adult and

juvenile plants, as did Two-Mile Lake, which was not found to suffer the winter die-off.

6.3.4.3. Potamogeton perfoliatus – Widespread colonisation.

This taxa was not recorded in the November 2001 survey, but was found in many locations by

February 2002 and became widespread later in 2002. Potamogeton colonised bare substratum

(mainly sandy locations) in many areas of the Broadwater, Two-Mile Lake, and Violet Hill in

early 2002, and was well established in the Broadwater in Autumn 2002. In particular the

northern and southern shores of the eastern Broadwater became densely populated with this

species, perhaps utilising free space created by the decline in the density of mature Vallisneria

plants at around the same time. In late 2002 this species was present in approximately 570

hectares of lakebed, perhaps growing from seeds which had been dormant.

6.3.5. Benthic Survey - Results and Discussion.

The results of the benthic surveys were plotted in a GIS application and the contours of

nutrient gradient were extrapolated to form the maps shown in Figure 6.13 to Figure 6.16. The



data used combines the 2000 Geosciences Australia survey of the Broadwater, as well as the

recent DIPNR 2002 work in other parts of the lake. To check for temporal differences that

might make combining the datasets unwise, samples were taken close to the 2000 survey

locations and were analysed in this study. No significant differences were shown for the

grainsize or nutrient content of sediments taken in 2002 when compared to 2000.

6.3.5.1. Percent Total Organic Carbon (TOC).

There was a general gradient of higher percent TOC with increasing distance from the

Broadwater. While TOC was generally below 10% of dry weight of sediment in the

Broadwater, very high percent TOC was found in Myall Lake, with some locations exceeding

25%. However, sandy areas of Myall Lake (eg. Neranie Sands and Palmers Bay) had similar

values to the sandy benches of the Broadwater. The Mid-Lakes had TOC of between 10% and

15%.

As was mentioned in Chapter 5, this distribution is probably a result of a low load of

suspended inorganic clay and silt being transported into Myall Lake and a high amount of

deposition of plant material on the lake bed following the Najas and Charophyte blooms that

occur each summer.

6.3.5.2. Total Nitrogen (TN).

The concentration of TN in sediments was very highly correlated with TOC and consequently

the distribution of TN mirrors that for TOC. Again, far higher concentrations of TN were

reported in the benthic material from Myall Lake, than were found in the Broadwater.

Sediments from the Broadwater and Nerong / Upper Myall River contained less than 10

gN/kg dry sediment, as did the southern portion of Two-Mile Lake. In contrast ‘The Narrows’

(northern Two-Mile Lake) Boolambayte Lake and Myall Lake had concentrations as high as

30 gN/kg, except in sandy areas which were less than 5 gN/kg.

6.3.5.3. Total Phosphorus (TP).

In contrast to Total N, Phosphorus concentration in benthic material was poorly correlated

with sediment TOC and was similar throughout the lake system. Generally, the greatest

concentrations were found in the deeper parts of each lake system (> 1 gP/kg dry sediment),

and shallow sandy areas had the lowest concentrations (<0.01 gP/kg dry sediment), but there

was considerable variability in the concentration found in similar areas. For example two

nearby locations in Myall Lake of similar depth had respective concentrations of 0.26 gP/kg,

and 0.82 gP/kg, which is more than a three-fold difference.



6.3.5.4.Total Sulphur (TS).

While sulphur is an important macronutrient for plant growth, it is less common for it to be

present in limiting concentrations in estuarine waters because of the high concentration of this

nutrient in seawater (Waite, 1984). The concentration of this element in the benthic material

of this system was the converse of what might be expected. With the lowest concentrations

being present in areas closest to the source of seawater (ie. the Broadwater) and much higher

concentrations being found in all other parts of the system. Equally high (>2 gS/kg dry

sediment) concentrations were present in Nerong Creek, the Upper Myall River, and many

parts of Myall Lake, while concentrations of <0.01 gS/kg dry sediment were typical of sandy

locations in all areas.

6.3.5.5. Grainsize Analysis.

No data is presented for this analyte. The method utilised in this study to perform grainsize

analysis, using the dispersal of laser light in a slurry of suspended sediment sample in liquid,

returned results that were in conflict with simple observations of sediment properties. It is

thought that because of the physical properties of the benthic material (containing mucous and

algal colonies) an unrepresentative value of each size category was reported.

A small recent survey of grainsize using conventional methods found significantly different

results to those returned by the laser scattering method (Pers. Comm. A. Kubiak, Masters

candidate The University of Sydney). Consequently the grainsize data are not being presented

for this survey.



Figure 6.13. Benthic percent TOC – September 2002.

Figure 6.14. Benthic Total Nitrogen – September 2002.



Figure 6.15. Benthic Total Phosphorus – September 2002.

Figure 6.16. Benthic Total Sulphur – September 2002.

mg/kg)

>1000



6.3.5.6. Benthic Microcystis sp.

In mid 2001, bathometric surveyors reported the presence of an unconsolidated organic

benthic material in much of Myall Lake. It was noted because it created difficulties in

mapping the lakebed, due to its ability to absorb sonar signals. The Myall Lakes vegetation

surveys that were began in November 2001 also noted in shallow bays the occurrence of a

highly organic, algal-like material that resembled decomposing plant material. It was also

noted that large amounts of gas which smelt strongly of Hydrogen Sulphide (H2S) were

liberated by the movement of boats in these shallow bays.

Some preliminary investigations revealed that the material was composed of high densities of

algal cells which were grouped into colonies and bound in a mucous matrix. Some of the cells

were also thought to resemble various blue-green algal taxa including Aphanothece and

Microcystis although the exact identity of the cells was unclear. Samples that were

subsequently identified by DIPNR were initially thought to be Microcystis, although the

material was unlike samples encountered before. In particular the fact that the material was

benthic and sheathed in mucous did not conform to known descriptions of this taxon.

Although the discovery of the benthic microbial material was incidental to the vegetation and

sediment surveys, a small survey was undertaken to map the distribution of the benthic

microbial layer in Myall Lakes, and commence some investigations into the identity of the

organism. Because of the initial finding of the similarity of the organism to Microcystis, a

mouse bioassay was conducted on samples taken from shallow bays. This analysis found that

4 of the 5 samples submitted were mildly hepatotoxic.

In early 2002 numerous samples were dispatched to laboratories in Australia and one in the

U.K. and toxicity testing was conducted to search for microcystin and cylindrospermopsin

toxins. The results of these analyses were inconclusive and in conflict between laboratories.

In mid 2002 DIPNR initiated formal investigations into the genetic sequencing of the

organism to identify the similarity of the alga to known blue-greens, and to identify the

presence of genes that coded for the production of microcystin toxin. The work being

performed by Brett Nielan of the School of Biotechnology and Biomolecular Sciences, at The

University of NSW.

In late 2002 it was found that the main organism in the benthic microbial layer was a

previously undescribed species that had a high (96% similar) genetic similarity to Microcystis

flos-aquae, a taxon known to be able to produce microcystin under some circumstances.

Further investigations found that genes that enable the organism to produce microcystin toxin



were also present, but that gas vacuoles, that might enable the cells to become buoyant, were

lacking.

In conjunction with the benthic nutrient content assessment in late 2002 (section 6.3.5),

samples were also qualitatively assessed for the presence of the new Microcystis organism in

all samples by examining a small sample under compound microscope. It was found that the

organism was present in variable densities in nearly all samples except those taken in the

Broadwater, Nerong Creek, and Myall River. Although the numbers of colonies per unit

volume was not quantified, it seemed that sandy areas of Myall and the Mid Lakes had little

or none of the organism, while the shallow bays where the organism was first observed had

the highest density of colonies. Based on the observed distribution there is approximately

7,500 hectares of lakebed which contains these cells in variable densities.

The distribution of the benthic Microcystis sp. corresponds well with initial field observations

of benthic material quality which noted (before the organism was identified) that the benthos

in some areas had a cohesive quality that was unlike usual estuarine or lacustrine muds. This

was distinct to the shallow bays, which appeared like composting vegetation. In particular

cores taken from the bed of the upstream lakes have a consistency similar to jelly, which can

be ‘fractured’ along lines into smaller pieces which retain a firm character. It would seem then

that the jelly-like character may be a consequence of much microbial material on the lakebed,

and that, the Microcystis sp. may play a significant role in the ecology of these areas and the

lake as a whole.

6.4. DISCUSSION.

Discussing the findings of these surveys is extremely difficult because of the unique benthic

microbial layer which appears to play a very important role in determining the character of

much of the system. Interpreting the significance of both the distribution of vegetation types

and benthic nutrient concentrations are confused by the presence of the benthic microbial

layer which is probably an important link in understanding the ecology of the lakes. In the

absence of definite knowledge of the role of the microbial layer, the discussion following

attempts to draw some conclusions about the vegetation and benthic nutrient surveys.

6.4.1. Vegetation

Vascular plants.

A clear distinction between the character of the Broadwater and Two-Mile Lake (the

downstream lakes), and that of Myall and Boolambayte Lakes (the upstream lakes) was

found. In brief, while the downstream lakes contain large areas of perennial angiosperm



macrophyte beds which persist throughout the year, the upstream lakes are dominated mainly

by annual / ephemeral plants and macroalgae, which demonstrate a more seasonal cycle.

Generally, it would be assumed that the absence of these perennial plants is a sure sign of

poor aquatic health and that the waterway is in decline. Adams et al. (1999), for example

describe the loss of perennial macrophytes as one of the steps that occur in the progression of

a eutrophied waterway degrading into a disturbed, algal-dominated system. It is confusing

then that the highest water nutrient concentrations and the least light penetration (Chapter 5)

were usually found in the Broadwater than other parts of the system, and then largest beds of

macrophytes are also present in this waterway.

Similarly, finding that ephemeral plants are dominant in Myall Lake would normally lead to

the conclusion that this waterway was in poor health, and that excess nutrients were likely to

be present in this waterway. Likewise, the high concentration of benthic nutrients (except

total phosphorus) and organic carbon in Myall Lake seems also to indicate that this waterway

is suffering from an overload of nutrient inputs and is in poor condition.

An alternative, more probable, model however could lie in the finding of large amounts of

benthic microbial material which seems to play a role in excluding the occurrence of

perennial macrophyte bed development. Much of the gently sloping or flat lakebed of Myall

Lake which would be expected to hold macrophyte beds is covered with the benthic

Microcystis sp. instead, while steeply sloping rocky areas nearby (which don’t allow the

retention of Microcystis sp) supports small healthy stands of these plants. While correlation

does not necessarily indicate causation, this anomaly implies that some mechanism may be

preventing the growth of perennial plants in areas that contain the benthic microbial layer.

It seems unlikely that competitive interactions (eg. shading or space monopolisation by

Najas) are excluding perennial macrophytes because of the complete absence of even juvenile

plants in areas containing Microcystis sp. and the fact that such plants are present in adjacent

rocky areas.

Whatever (if any) mechanisms are responsible for the exclusion of perennial macrophytes

from areas containing large amounts of benthic Microcystis sp. is presently unknown.

However, it is likely that it may be a combination of the lack of benthic attachment provided

by the material (all the perennial macrophytes in Myall Lakes are quite buoyant) and the

smothering or decomposition of propagules by microbial action, which contribute to the

prevention of macrophyte establishment.

Charophytes.



Although the distribution of perennial macrophytes in the lake system is counter to an

intuitive assessment of aquatic health (ie. there are few of these plants in the healthiest part of

the lakes), the distribution and abundance of charophytes is more in line with the perceived

and measured gradient of eutrophication. Many charophytes are only able to grow in low

nutrient (particularly phosphorus) conditions (Auderset-Joye et al., 2002), and have been lost

where nutrient enrichment of freshwaters has occurred. Some taxa are known to only occur in

groundwater-fed wetlands which are particularly low in phosphorus (Bornette et al., 1996).

Auderset-Joye (2002) described changes in the abundance in distribution of charophytes in

Swiss lakes since 1800 to 2000 using herbarium collections and contemporary sampling.

Much of the change found was centred around sites of nutrient enrichment of waterways. One

of the taxa found in that study showed that Nitella hyalina, which is abundant in Myall Lakes,

was adversely affected by increases in nutrients. Other studies in Australia on shorter time

scale have established correlations, if not causation, between elevated nutrients and declines

in charophyte abundance (eg. Casanova and Brock, 1999).

It is apparent then that fact that these plants which have been demonstrated to be sensitive to

eutrophication are abundant in Myall Lake and less so in the Broadwater is circumstantial

evidence of differences in nutrient loads. Other physical factors such as the widely different

salinity regime of each of these lakes, and different benthos, however clearly confound the

direct interpretation of this pattern of distribution. It is possible though, that these plants could

be a useful bioindicator of future environmental health in this system.

Although further study is required, if Nitella or Chara could be utilised as indicators of

environmental decline due to nutrient enrichment they could be a very valuable asset in

managing the future health of the lakes. To monitor changes in the presence of these taxa it

would be necessary to quantify the abundance (standing crop or productivity) of the plants.

The plants are distributed throughout the lakes, but are present only as small plants in the

Broadwater.

The absence of these plants in locations known to be high in nutrients, such as in the western

Broadwater, and the presence in the eastern Broadwater (noting physico-chemical water

quality is similar at each location), suggests that there may be a good correlation between

elevated nutrient concentrations and lack of plants in this system at present. Consequently, the

potential for charophytes to be used as a bioindicator in this system seems likely.



6.4.2. Benthic Nutrient Content.

It is clear that (apart from the sandy areas) the material on the bed of Two-Mile,

Boolambayte, and Myall Lakes is very high in nitrogen and, sulphur and organic carbon in

comparison with the Broadwater, and that there is a gradient of increasing concentration in

the Mid lakes region. As previously mentioned, the presence of high benthic nutrient content

is not necessarily an indication that there is significant nutrient being added to the water

column from the sediments, and this might only occur under conditions of benthic anoxia.

It is possible that the presence of photosynthetic Microcystis sp. and the addition of much

organic material following Najas and charophyte blooms in these areas, which presumably is

broken down by benthic microbes, has created a biologically active benthic layer which

contains much organic matter, both living and decomposing. As well, the main source of silt

and clay which might lead to a ‘dilution’ of benthic nutrient concentrations by weight, is

located in the Broadwater and the precipitation of particles before they reach the upstream

lakes means that little inorganic material is deposited.

The fact that Total Phosphorus is low in most samples in the upstream lakes suggests strongly

that this could be the limiting nutrient in these locations, although further studies would be

needed to confirm this.

6.4.3. General Discussion

The overall implications for the presence of a highly organic, and possibly biologically active

lakebed in managing the health of Myall Lakes is presently unknown. Apart from seemingly

influencing the types of plants that can grow in these areas a variety of more subtle ecological

affects might also exist that require further investigation.

Because the lakes are shallow and easily turned over, the respiratory oxygen demand of such

material is unlikely to cause deoxygenation of benthic waters, and the physico-chemical

measurements made have not found anoxia in bottom waters in these lakes. However, if

Myall Lake were to become stratified for an extended period it is possible low dissolved

oxygen could eventuate, which might have severe consequences for lake health.

Perhaps the greatest role the material may play in lake health is how it cycles nutrients within

the system. The benthic microbial material may at times serve as a scavenger of water-borne

nutrients which could be part of the reason that water column nutrients are typically lowest in

Myall Lake. As well, the material may play a role in cycling nutrients and releasing them to

fuel plant growth. In Chapter 5 a small study is reported into the concentration of nutrients

present in benthic waters of Two-Mile Lake. A high concentration of NOx was found over an



area known to contain the benthic microbial layer. As well, in the shallow bays where the

decomposing plant material and abundant Microcystis sp. are found the interstitial-water

ammonium concentration was found to be extremely high (~15 mg/L - Pers. Comm, Andrew

Sampaklis, Honours candidate, University of Newcastle, 2003).

It is clear that the benthic microbial material, because of its widespread distribution and

demonstrated high nutrient content, has the potential to play a significant role in mediating

and regulating the concentration of water column nutrients and physical water quality. Several

studies are presently underway to examine various aspects of this material’s qualities, which

will assist in understanding its importance for managing the lake’s ecology.

Although a full understanding of the influence of the benthos over the macrophytes of the

lakes is not possible at present, clear differences between the character of the two major

waterbodies (Myall Lake and the Broadwater) of this system are apparent. This disparity

presumably developed historically because of differences in the quality of water delivered to

the receiving waters of each lake, and the maintenance of each is reliant on the continuation

of those conditions.

Although water quality would have declined in recent years, the Broadwater probably always

has received intermittent fresh, turbid and somewhat nutrient-laden waters from the Myall

Catchment, and will continue to do so. Myall Lake on the other hand which is has clearly an

oligotrophic character, could be very badly harmed by declining water clarity and increased

nutrient loads.

As detailed in Chapter 5 upper Myall Rivermouth and Broadwater which are most susceptible

to reduced water clarity have the shallowest compensation depth. This means that any

decrease in water clarity in these areas due to increased turbidity in river inputs may decrease

the depth to which aquatic plants are able to grow. Depending on the bathometry of the

region, this may substantially reduce the area available for plant growth. At present,

macrophyte beds are restricted to the shallow areas of the Broadwater, indicating a response

to lower light levels

An increase in phosphorus and declines in water clarity in Myall Lake would undoubtedly

disturb the annual cycle of charophyte and Najas growth, which occupies the entire bed of the

lake including the deepest areas of the waterway. These changes would probably be noticed

first in the deeper areas of the lake, as lakebed illumination in these areas would be first to fall

below the required intensity required for plant growth. Whether or not the benthic Microcystis

sp. would be affected is unknown.

Chapter 7, Synthesis of the data. Understanding Blue Green Algae Blooms in Myall Lakes NSW.


7. Synthesis of the data.The 'Monitoring Blue Green Algal Blooms in Myall Lakes' project was designed to answer a

range of specific questions posed by the community and project sponsors regarding blue-

green algae in Myall Lakes and the overall health of the lakes system. The preceding chapters

in this report provide an introduction to the lakes system; background to the problem; and the

results of the various studies undertaken during the course of the project. This chapter

attempts to answer those questions, drawing on the information in the previous chapters.

Rather than repeating the information provided in the previous chapters, reference is made to

the relevant sections where appropriate.

7.1. WHAT ARE THE PHYSICAL AND BIOLOGICAL CONDITIONS / PROCESSESWHICH CONTRIBUTE TO BLUE-GREEN ALGAL BLOOMS IN MYALLLAKES?

Blue-green algae blooms in Myall Lakes were first confirmed in Bombah Broadwater in

April, 1999. These blooms were composed of large, toxigenic, scum forming species such as

Anabaena, and later Microcystis. These species were not recorded in bloom concentrations

after July 2000. However, in 2001 and 2002, small non-toxigenic species such as

Chroococcus and Merismopedia were recorded in Myall Lake and Mid Lake areas at levels

which caused a high alert status to be instated1. These two types of blue-green algae have

quite different characteristics and physiology including size, buoyancy and nutrient

requirements. Consequently, different taxa of blue-green algae will bloom in response to

different environmental conditions within the lakes at any given point in time.

7.1.1 Anabaena/Microcystis blooms in the Broadwater.

The environmental conditions which allow Anabaena and Microcystis to gain competitive

advantage over other phytoplankton species in waterways generally include warm water, low

salinity, elevated nutrient inputs and increased turbidity (see Chapter 4 for more detail). All

these conditions occurred during the period from April 1999 to July 2000 when blue-green

algal blooms, dominated by Mycrocystis and Anabaena, were recorded in the Broadwater.

Water temperatures range from 10 to 28?C in Myall Lakes annually and ranged between 11 to

23?C at the time of the blooms. Summer temperatures are favourable for blue-green algal

growth. During the period of the bloom, the salinity in the Broadwater was very low

(<2mS/cm). This was caused by moderate rainfall in the catchment in late 1998, followed by

large rainfall events in March and April 1999 (see section 2.2.1 for details for details on

1 High Alert for recreational use is 15,000 cells/mL for potentially toxic species or 2mm3/L for contactirritant species.



climate). It is likely that these inflows were large enough to cause the entire Broadwater to

become essentially fresh until July 2000. As salinity increased after this time, toxigenic blue-

green algae concentrations declined rapidly, and have not been recorded in bloom

concentrations since. Section 4.3.3 describes the relationship between the various algae taxa

and salinity concentrations. In Fig. 4.7 it can be seen that Anabaena and Microcystis

concentrations both decline rapidly after salinity concentrations exceed the 2 to 4 mS/cm

range.

The rain events of late 1998 and early 1999, would have also washed large quantities of

nutrients into the Broadwater. Studies in 2001/2002 have shown that the catchment of the

Upper Myall River can produce up to 45.1 tonnes of nitrogen (N) and 9.4 tonnes of

phosphorus (P) in a single rain event (Chapter 3). Modelling of nutrient generation for the

Myall Lakes has shown that contributions from the catchment are a major source of nutrients.

Phosphorus concentrations in the water column were often high at the mouth of the Upper

Myall River, and in the Broadwater throughout this study, also indicating the Upper Myall

River is the main nutrient source to the Broadwater. Delivery of Phosphorous through

sediment recycling is also a potential source, however, preliminary studies (AGSO, 2000) on

this were inconclusive.

It is also likely that light penetration in the Broadwater decreases during large flow events due

to large loads of sediment washed in from the catchment. Even in dry periods, the Broadwater

has relatively lower clarity because of tannins in the water, and wind driven re-suspension of

fine particles from the bottom (this is discussed in more detail in Chapter 5). . Because both

Anabaena and Microcystis have the ability to control their buoyancy, and hence where they

are positioned within the water column, they are able to outcompete other species when light

penetration into the water column is low.

7.1.2 Chroococcus dominated assemblages in Myall Lake .

Although the Anabaena and Microcystis blooms occurred primarily in the Broadwater and

Two Mile Lake, extensive sampling throughout the Myall Lakes was undertaken to determine

the spatial extent of the bloom. In October 2000, high biovolumes of blue-green algae were

detected in Myall Lake and continued sporadically during the life of the project. These

blooms were composed of a mixed assemblage of small species usually dominated by

Chroococcus and occasionally Merismopedia. These species produce compounds (ie. toxins)

which cause skin irritation. They do not produce the neurotoxins and hepatotoxins that are

typical of Anabaena and Microcystis respectively and therefore are less harmful to human

health. These algae are not as visible as the Anabaena/Microcystis blooms as the cells are not

buoyant, and therefore remain well mixed through the water column.



It is impossible to know for certain whether or not these species were present in Myall Lake

in large numbers prior to April 2000 due to infrequent sampling and the use of laboratory

techniques that were mainly intended to assess human health risks from large-celled

(toxigenic) blue-green taxa. After April 2000 a different laboratory method was employed,

which found small-celled taxa in low concentrations in Myall Lake and Violet Hill. After

April 2000 monthly sampling (except for August and September 2000) at these locations

found low concentrations at most sites until December 11th, 2000, when all samples from the

upper system were found to contain elevated concentrations of small-celled blue-green algae.

Although the general pattern of low abundances of small-celled taxa in winter, and a bloom in

Spring that was observed in Myall Lake in 2001 and 2002 was the same in 2000 (Chapter 4,

Figure 4.4) there was a significant difference in the composition of the blue-green algae.

While the spring blooms of 2001 and 2002 were dominated by Chroococcus, with low

numbers of Merismopedia being present, the opposite was true in 2000, Merismopedia being

dominant and Chroococcus being either absent or scarce until January 2001. This distinct

difference between 2000 and the subsequent 2 years could indicate a succession of these two

taxa, and that the environmental disturbance shown in the Broadwater in 1999/2000 was

being reflected in the ecology of the phytoplankton in other parts of the lake system.

Conditions that are likely to favour these small species over other algal groups, such as

diatoms or green algae, are nitrogen enrichment, silica limitation (disadvantaging

competitively superior diatoms), clear water and a well mixed water body. Also, if the bloom

and succession of Merismopedia / Chroococcus was a result of disturbance elsewhere in the

lake system, subtle ecological changes may also have had an influence on the appearance of

these taxa.

During the study, there was some evidence of nutrient enrichment in Myall Lake with

extremely high values of ammonium (NH4+) recorded at times. Small blue-green algal species

do not fix nitrogen and thus thrive in conditions of high nitrogen availability, particularly

NH4+. As there is no major riverine inflow into Myall Lake, the NH4

+ is likely to be

regenerated from the sediments. The floor of Myall Lake is covered in a highly organic layer,

which may be involved in the release of NH4+ into the water column from the sediment under

certain conditions.

Silica is required by diatoms for incorporation in their cell walls. In low silica conditions

(<0.5 mg/L), they are unable to compete effectively with non-siliceous algae (Wetzel and

Likens, 2000). Creeks and rivers are the main source of reactive silica in coastal waters.

Given the large distance from major riverine inputs to Myall Lake, silica limitation in Myall



Lake is a possibility. Low concentrations of soluble silica (<0.3 - 1.8 mg/L) were recorded in

Myall Lake in 1972-1973 by Johnson (unpublished manuscript). In September 2000 reactive

silica from all locations throughout the lake system reported values below 0.1mg/L.

The clarity of the water in Myall Lake was consistently higher than in other parts of the lake

throughout this study. In addition, the water body is relatively stable as it has a long residence

time and is not greatly influenced by riverine inflows. It is also well mixed by wind. As small,

blue-green algal taxa are not able to regulate their position in the water column, a well-mixed

water body with adequate light throughout for photosynthesis would create favourable

conditions for their growth. In addition to this, the smaller celled species appear to have a

greater tolerance of increased salinity levels. This gives them an advantage over larger celled

species (Microcystis and Anabaena) in conditions of high water clarity, low P / high N, and

relatively increased conductivity.

The differing characteristics of the Myall Lake from the Broadwater appear to influence the

type of algae taxa present at any given time. It is only after prolonged rainfall, and hence

displacement of saline water by turbid freshwater in the Broadwater, that toxic blooms of

Anabaena and Microcystis are likely to occur. The conceptual diagrams (Figures 7.1 and

7.2), provide a pictorial representation of the factors which lead to the development of algal

blooms on Myall Lakes.



7.2. WHAT ARE THE RELATIVE CONTRIBUTIONS OF NUTRIENT SOURCESTO ALGAL GROWTH IN THE LAKES?

7.2.1. The role of nutrients in algal growth

Nitrogen (N) and phosphorus (P) are the nutrients that most often limit algal growth in aquatic

and estuarine environments. These nutrients must be in a dissolved inorganic form – nitrogen

as ammonium (NH4+) and nitrate (NOx) and phosphorus as phosphate (PO4

-) – to enable

uptake by algae. The amount and availability of nutrients in a water body will depend on the

form in which they are delivered, and cycling of nutrients and organic matter within the lake.

7.2.2. Sources of nutrients to Myall Lakes

Nutrients enter Myall Lakes through a number of sources including rainfall, groundwater,

surface runoff and riverine inflows. The relative contribution of each source is summarised

below (further detail can be found in Chapter 3). Once nutrients enter the lake, they are cycled

through aquatic plants, algae (including macroalgae and phytoplankton) and sediments. These

processes are important in a very enclosed system like Myall Lakes, as there is little export of

nutrients from the system through flushing. It is important to make the distinction between

external nutrient sources, and internal nutrient cycling. Under certain conditions, internal

nutrient cycling may return nutrients to the water column to stimulate algal blooms. However,

they do not represent a new source of nutrients to the lake.

7.2.2.1 Rainfall

Rain contains small amounts of nutrients often associated with dust particles. The

contribution of rainfall directly to coastal waters is generally considered small or negligible.

However, Myall Lakes has a large surface area (>100km2) and although the amount is only a

small proportion of the annual budget, the contribution of direct rainfall is significant. Direct

rainfall was calculated to contribute 1.3 tonnes of P and 10 tonnes of N per year, which is

approximately 10% of total annual load from the catchment, in an average rainfall year.

7.2.2.2 Groundwater

There are no accurate quantitative estimates of groundwater discharge to Myall Lakes (MHL

1998) (see Chapter 3). Therefore nutrient concentrations of ground water cannot be used to

calculate an accurate nutrient load to the lake. Results of groundwater testing showed that

nitrogen concentrations were naturally high even in areas remote from human activity. Some

contamination of groundwater with nutrients, especially during summer was detected near

camping grounds at White Tree Bay and Myall Shores Resort. Most nutrients generated by



anthropogenic activities undertaken on the foreshores are delivered to the lakes system via

groundwater. Nevertheless, as discussed in the following section, these do not represent a

major contribution to overall nutrient loads.

7.2.2.3 Catchment Inflows

Riverine inflows during wet weather events were shown to be the largest source of nutrients

to Myall Lakes. These flows carry nutrients and sediment generated in the catchment through

activities such as soil erosion (sheet, rill, gully, and streambank), sewage disposal, intensive

agriculture, fertiliser application and clearing of vegetation. The main riverine input into

Myall Lakes is the Upper Myall River, which flows into the western edge of the Broadwater.

A much smaller riverine input is made by Boolambayte Creek, which enters at Two Mile

Lake.

Estimates of the nutrient loads delivered to the lake from each catchment, and from foreshore

areas of Myall Lakes were modelled using the Catchment Management Support System

(CMSS). This modelling identified the catchment of the Upper Myall River as the major

contributor of nutrients to Myall Lakes, and highlighted dairy farming and poultry farming

(assuming the litter is spread within the catchment) activities as significant contributors,

particularly, given the relative area of land they occupy. The annual load of nutrients from the

catchment of the Upper Myall River was estimated to be 96.5 tonnes of N and 12.8 tonnes of

P per year which represents 70% and 80% of the annual load of N and P respectively, from all

catchment sources.

Results of sampling during rain events by an autosampler stationed at Bulahdelah were in

close agreement with estimates of nutrient loads obtained by modelling. Up to 45.1 tonnes of

N and 9.4 tonnes of P were calculated to be delivered to Myall Lakes in a single rain event of

270 mm. Modelling (using the CSIRO developed SEDNET model) is currently being

undertaken in the Myall Lakes catchment to allow better pinpointing of diffuse nutrient

sources.

7.2.2.4 Nutrient recycling within the lake

Myall Lakes acts as an effective trap for nutrients and sediment due to its naturally limited

capacity to export nutrients and sediment to the ocean through tidal exchange. Therefore the

internal cycling of nutrients within the lake is likely to be very important in nutrient dynamics

and algal growth. Inorganic (bioavailable) nutrients that enter the lakes from the catchment

are likely to be rapidly consumed by phytoplankton and macroalgae. When these algal cells

die, they sink to the bottom of the lake and decompose, and under certain conditions the



nutrients can be released back into the water column. Significant amounts of nutrients are also

delivered from the catchment attached to sediment particles and organic matter, which sinks

to the lake bed. Nutrients that reach the lake bed are recycled through complex bio-

geochemical cycles. These cycles do not represent a new source of nutrients to the lake

system, rather they are pathways by which nutrients delivered from external sources are

processed. These processes may either remove nutrients from the lake through burial in lake

sediments, remove nitrogen through denitrification, or, under certain conditions, release

inorganic (bioavailable) nutrients to the water column that are then available for algal growth.

In Myall Lakes, two preliminary investigations have been undertaken to examine the potential

of nutrient release from the sediments (the AGSO study described in Chapter 2 and the near-

benthic and benthic sampling described in Chapters 5 and 6 respectively). The former study,

although restricted to the Broadwater, showed that denitrification efficiency was low in

muddy sediments, and that significant quantities of ammonium (NH4+) were returned to the

water column, which could potentially fuel algal blooms. The amount of inorganic

phosphorus (PO4) released from the sediments was small. However, phosphorus release

usually requires low oxygen conditions, which did not occur at the time of the study, but have

been recorded in the Broadwater at other times.

The denitrification efficiency recorded in muddy sediments in the Broadwater at the time of

the study is comparable to other estuarine sites in Australia which are considered eutrophied.

Low denitrification, and release of ammonium and phosphorus, is increased in conditions of

high organic loading, low oxygen, and high turbidity which decreases light penetration to the

sediment surface. These conditions occur with increases in nutrient and organic matter loads

from the catchment. In contrast, reducing the nutrient and organic carbon load will create

conditions which are suitable for increasing denitrification and a reduction in the flux of

nutrients from the sediment. While internal nutrient cycling may play an ongoing and

important role in algal growth for some time, the loads entering the system from the

catchment are the main area where action to reduce nutrient inputs will be most effective.

Reducing the nutrient loads entering the lake is likely to reduce the intensity or frequency of

algal blooms.

The studies described in Chapters 5 and 6 also support sediment nutrient release as a mode of

fuelling algal blooms in the lake system. In particular, the role of the Microcystis sp. layer in

nutrient recycling (particularly N) requires further investigation in Myall Lake, where it is

hypothesized that the majority of N that fuels algal blooms is derived from benthic sources.



7.2.3. Summary of nutrient source data:

One of the key issues, which this project has attempted to understand, is the source and role of

nutrients in the establishment of blue-green algal blooms in the Myall Lakes system. From the

assessment of nutrient sources to the lake system it has been shown that there is significant

delivery of nutrients to the lake system in freshwater inflows. However it is the cumulative

impacts of the freshwater inflows over time which is the most significant issue or factor in the

development of blue-green algal blooms in the Myall Lakes system.

The assessment of sources and contributions of nutrient to the Myall Lakes (which is

summarised in Table 7. 1) identifies nutrient inflow from the catchment as the major

contributor of nutrients to the lake system. The inclusion of estimates describing rainwater

and groundwater contributions provides contextual data reflecting the ‘natural’ nutrient

cycling in the landscape.

7.3. WHAT IS THE NUTRIENT STATUS OF MYALL LAKES?

Determining the nutrient status of a coastal water body is a difficult task primarily due to the

non-linear responses of aquatic systems to nutrient loads, and intermittent nature of nutrient

delivery. Aquatic ecosystems that are oligotrophic may ‘switch’ to eutrophic conditions

relatively quickly. Other factors that complicate the task of assessing nutrient status in coastal

waters include:

? High natural variability of many parameters used to assess nutrient status (nutrient

concentration and loads, chlorophyll - ? , phytoplankton composition),

? Complex, long term changes in parameters due to factors other than nutrient loading eg.

water quality (other than nutrients), seasonal effects, or species specific responses,

? Differences in the pathways for nutrient cycling between fresh and estuarine systems,

? The effect of water body residence times on nutrient cycling and susceptibility to nutrient

loads,

? The influence of drought and flood conditions on timing of delivery of nutrients, and

changes to water quality parameters.

While the occurrence of toxigenic blue-green algal blooms in the Broadwater is a likely

symptom of eutrophication, an assessment of the nutrient status of Myall Lakes should

incorporate a range of characteristics of the system.



7.3.1. Techniques to assess nutrient status

An assessment of nutrient status is particularly difficult in Myall Lakes given its unusual

characteristics. These include changes in nutrient chemistry and water quality parameters

associated with long term changes in salinity; considerable differences in character and

ecology between interconnected lakes, and little previous information on the water quality

and phytoplankton communities. However, there are a number of ways in which the

information collected during this project can be used to make a preliminary assessment of the

nutrient status of Myall Lakes. These include:

? comparing the characteristics of Myall Lakes with known signs of eutrophication based

on research in other coastal lakes; and

? sustainable loads assessment - comparing nutrient loads to Myall Lakes with other NSW

coastal lagoons.

7.3.1.1 General signs of eutrophication

Evidence from a large number of studies from Australia and around the world have shown

that the general characteristics of eutrophication of coastal lakes include:

? changes in the composition of the phytoplankton community with dominance by blue-

green species;

? an increase in frequency of filamentous and phytoplankton algal blooms, and decline in

macrophyte and seagrass communities;

? an increase in plant and animal biomass;

? a decrease in species diversity;

? a decrease in water clarity;

? an increase in sedimentation;

? the development of anoxia; and

? high organic loads in the sediment.



It is important to note that short term trends in these parameters may simply be responses of

the system to natural variations, and that there is little information for Myall Lakes to enable

assessment of long term trends.

7.3.1.2 Sustainable loads of nutrients

Scanes et al. (1997) applied a nutrient assessment to a range of NSW coastal lakes, by

comparing catchment nutrient loads with a subjective index of degradation based on

characteristics of each system. From this, a risk assessment for coastal lakes from catchment

loads of nitrogen and phosphorus was derived and estimates of sustainable loads of nutrients

to coastal lakes developed. This assessment was applied to Myall Lake by comparing loads of

nutrients to the Broadwater, Mid Lakes and Myall Lakes to these risk categories (Scanes et

al.1997).

7.3.2. Assessing the nutrient status of Myall Lakes

Due to the large differences in physical and biological characteristics among the different

lakes, the nutrient status of the Broadwater, Mid-Lakes and Myall Lake will be assessed

separately.

Table 7. 1 Nutrient status of Myall Lakes compared to sustainable nutrient loadassessment of Scanes et al. (1997).

Risk of EutrophicationLake Nutrient Averageweather Load

(Tonnes/km2/yr)Low Moderate High

Broadwater Nitrogen 4.6 ?Phosphorus 0.6 ?

Mid-Lakes Nitrogen 1.0 ?Phosphorus 0.1 ?

Myall Lake Nitrogen 0.3 ?Phosphorus 0.02 ?

Note that loads are calculated for average rainfall for nutrient runoff from the catchment and may underestimate actual loads as

this assessment does not account for movement of nutrients between lakes or contributions from regenerated nutrients in

sediments.

7.3.2.1 Broadwater

Of the three lakes, the Broadwater receives the highest nutrient load from the catchment, has

experienced toxigenic algal blooms, has relatively lower water clarity, low denitrification

efficiency of muddy sediments, and some areas of filamentous macroalgae. These

characteristics would indicate a eutrophic status. However, there are large areas of healthy

macrophytes, no evidence of anoxia, and a relatively diverse fish community that forms the



basis of an ongoing commercial fishery. These characteristics would indicate an oligotrophic

or mesotrophic status.

The conditions which trigger toxigenic blue-green algal blooms in the Broadwater are

associated with high rainfall events – fresh water, high nutrient loads, and turbid conditions

(Chapter 4). During periods of below average rainfall, the Broadwater does not exhibit

sustained algal blooms. If this area were in a highly eutrophic status, it would be expected that

macrophyte communities would decline. Phytoplankton blooms would persist during low

rainfall periods, with the dominant species shifting from blue-greens to dinoflagellates with

increasing salinity. There may also be reports of bottom water anoxia and associated fish kills.

It appears then, that the Broadwater does experience periods of eutrophication associated with

high rainfall events, but is able to ‘recover’ to a mesotrophic status during periods of low

rainfall (see Figures 7.1 and 7.2).

According to the model of Scanes et al. (1997), the estimated nutrient load to the Broadwater

under average rainfall conditions places the Broadwater in Moderate Risk category for

eutrophication. However, studies in March 2001 showed that up to 43% and 67% of the

annual loads of nitrogen and phosphorus respectively were delivered to the Broadwater in a

single rain event. The risk of eutrophication would then be significantly increased during

these wet weather events.

This is an early warning sign that unsustainable loads of nutrients are reaching the Broadwater

and there is potential for the system to switch to a eutrophic status if nutrient loads continue.



Figure 7. 1 Conceptual diagram showing nutrient loading to the Broadwater underconditions of large freshwater inflows.

Figure 7. 2. Conceptual diagram showing system functioning in dry weather.



7.3.2.2 Myall Lake

Myall Lake is the largest of the three lakes, has no major riverine input and is furthest from

tidal exchange. Consequently it has an extremely long flushing time. Its phytoplankton

assemblages are diverse and are dominated by non-toxigenic blue-green species and green

species, some of which are typical of eutrophic lakes; the sediments have an extremely high

organic carbon and total nitrogen content (see Chapter 6); and the water column concentration

of ammonium is sometimes extremely high (see Chapter 5). These conditions would indicate

a mesotrophic or eutrophic status. However, it is also characterised by low estimated nutrient

loads, large seasonal blooms of macroalgae, particularly charophytes; clear water; low

phosphorus concentrations in the water column and sediments, and has not experienced

blooms of toxigenic blue-green algae. These characteristics would indicate an oligotrophic

status for this lake, with characteristics indicating it is limited by phosphorus.

There are a number of factors that may influence the particular characteristics of Myall Lake.

The absence of large blooms of toxigenic blue-green algae may be due to phosphorus

limitation. The main source of phosphorus to Myall Lakes system is the Upper Myall River,

which would be diluted and absorbed in the Broadwater and Mid-Lakes over the 10-15 km

distance to Myall Lake. The dominance of species other than diatoms may be due to very low

levels of silica in Myall Lake. The presence of Najas, rather than perennial macrophytes may

be due to a lack of suitable substrate due to the flocculant, organic nature of the lake bed (see

the description of the Mycrocystis layer in Chapter 6). Rooted macrophytes such as

Vallisneria occur in Myall Lake, but only in rocky areas. The charophytes that occur in Myall

Lake are typical of freshwater systems with low phosphorus inputs. However, these are very

sensitive to nutrient sources and cannot physiologically tolerate elevated nutrient

concentrations.

Estimates of nutrient load (Chapter 3) would place this area in a low risk category for

eutrophication according to Scanes et al. (1997). However, given its unique characteristics

and extremely long flushing time, the susceptibility of this lake to any increase in phosphorus

loads is extremely high.

7.3.2.3 Mid-Lakes

Two Mile and Boolambayte Lakes lie between the Broadwater and Myall Lake and have

intermediate characteristics between the two. The Mid Lakes has a moderate nutrient load,

has experienced some toxigenic algal blooms, has moderately low water clarity (compared to

Myall Lake), moderate to high organic carbon and nitrogen in sediment. Again, these



characteristics would indicate a mesotrophic to eutrophic status. However, macrophyte

communities are diverse and composed of both rooted and floating species and the water is

relatively clear. These characteristics would indicate an oligotrophic to mesotrophic status.

According to the sustainable nutrient model (Scanes et al, 1997) estimates of nutrient load to

the mid lakes would place it at the upper end of the low risk category for eutrophication in

average rainfall conditions, but would probably be in the Moderate Risk category during rain

events.

7.3.3. Risks due to increasing nutrients

The Broadwater is the lake that is most susceptible to existing nutrient loads carried in by the

upper Myall River from the catchment. It exhibits characteristics that favour blue-green algae

under high rainfall conditions. At present it is able to recover from these events during periods

of low rainfall. However, if the nutrient load is not reduced, the Broadwater is likely to show

signs of eutrophication (algal blooms, low oxygen, and loss of diversity) even in periods of

low rainfall.

Myall Lake is presently oligotrophic to mesotrophic but there is an extremely high risk of

eutrophication from any increase in phosphorus loads to the lake from catchment sources. If

phosphorus load increases and clarity decreases, it is likely that the Najas will be lost and the

lakes may switch to a phytoplankton dominated system, with toxigenic blue-green algal

species occurring. Its low level of connectedness from direct catchment inputs, however,

provide it with some level of protection. High organic Carbon levels in the sediment are

speculated to be the result of decay, over long time periods, of the annual (prolific) growth of

Najas and also reflect very little delivery to the system of sediment-laden, turbid waters from

the catchment. The role of the Microcystis layer in recycling N and its potential contribution

to growth of Chroococcus requires further study.

The Mid Lakes has characteristics which are intermediate between these two systems. It has

lower nutrient loads than the Broadwater, but the presence of charophytes indicates it is also

at risk from increases in nutrients, particularly phosphorus.



7.4. SUPPORTING THE DEVELOPMENT OF EFFECTIVE MANAGEMENTSTRATEGIES TO REDUCE CATCHMENT LOADS

Information gained from studies to investigate the ecology and nutrient status of the Myall

Lakes system has been used to formulate broad catchment based strategies and to develop

priority actions to reduce the risk of future blue-green algal blooms. The key theme from this

work is the need to adopt nutrient management activities in the catchment. The focus of these

are reducing nutrients at the source and promoting strategies to intercept and reduce

movement of nutrients into waterways.

Information from the Myall Lakes investigations suggests that there may be a long time frame

before management actions will deliver an outcome due to the potentially significant internal

nutrient loading in the system. The challenge for the community, resource management

agencies and local authorities is to be able to understand the implications of these findings

and to ensure that realistic expectations can be established.

7.4.1. Regional Strategic Focus: Lower North Coast Catchment Blueprint.

In early 2000, Catchment Management Boards (CMBs)2 were established by the NSW

government to strengthen the community-government partnerships in managing natural

resources. These catchment management boards are comprised of membership from rural

landholders, the Aboriginal community, nature conservationists, local government and state

government representatives.

The Lower North Coast Catchment Management Board (LNCCMB) area covers approx 13

200 km2 and includes the Manning, Wallis Lake, Smith Lake, Myall and Karuah catchments.

The catchment board has developed an Integrated Catchment Management Plan for the Lower

North Coast which has been "designed to provide direction and priorities for the investment

of funds and activities by our community, industry; local and state governments; to manage

and improve our natural resources" (DLWC, 2003).

The Catchment Board’s Integrated Catchment Management Plan has identified a number of

targets with regard to managing the areas terrestrial biodiversity, soil health, aquatic health,

and water quality. The Board has recognised blue-green algal blooms in the Myall lakes as a

significant natural resource management issue for the Lower North Coast and has endorsed

targeted actions to deal with the issue of nutrient management in the Myall Catchment.

2 Catchment Management Boards have now been replaced by Catchment Management Authorities.The former LNCCMB has now been incorporated into the Hunter / Central Rivers CatchmentManagement Authority (HCRCMA). While specifics of the LNCCMB Blueprint may change, theintent will remain the same.



A Lower North Coast Catchment Board water quality target has been established with the

goal of reducing total phosphorus levels in the Myall River (a high priority river)3 by 10 % by

the year 2012. In establishing this target the catchment board recognised the importance of

reduction of all nutrients entering the waterways and was conversant with the data showing

correlations between total P levels and Total N levels for the Myall River. Hence the decision

for the use of total P as an indicator for nutrient management success. Monitoring programs

established to report on this target include monthly nutrient and storm event sampling to

report on catchment loads together with proposals to further develop catchment nutrient loads

as a co-operative project with CSIRO using SedNet catchment modelling programs.

Management targets, among others, identified / endorsed by the LNCCMB targeted at

improving water quality in the Myall River include;

? 100% adoption by landholders of BMPs for chicken litter use and diary effluent

management of farming lands by 2005;

? development of off stream watering / riparian fencing / restricted access to waterways;

and

? promotion of strategies to maintain / enhance / net gain of effective and functioning

riparian / littoral vegetation.

The LNCCMB has used the knowledge gained from the investigations into the causes of the

Myall Lakes algal blooms to endorse a general catchment wide approach for the reduction of

nutrients entering coastal waterways in all river systems in the catchment board area. The

LNCCMB has also recognised that co-operative community action is required to address the

issue of nutrient management at a catchment scale. As such, it has endorsed priority

management actions that support the development and capacity building of community

groups and funding for implementation of Community Catchment Plans.

7.4.2. Local catchment Level : Myall Community Catchment Plan

A cooperative project was developed between the community and DIPNR to oversee the

development of a community catchment plan to tackle land degradation and water quality

issues in the Myall Lakes' catchment. The outbreak of the blue-green algal blooms in the

Myall Lake system providing the catalyst for the Plans’ development.

3 High priority rivers are those that have been determined by DIPNR and the CMB to have the mostelevated levels of phosphorus and nitrogen in the Lower North Coast catchments.



To oversee the development of the plan a 'Catchment Planning Group' was formed, with

representatives from government agencies and a broad cross-section of the community

including cattle, dairy/chicken farmers, environmental, land-care, chamber of commerce,

tourism and the Myall Lakes Blue-green Algae Action committee representation.

The Myall Lakes Community Catchment Management Plan identifies a number of objectives

that describe long term goals for the management and/or control of the land management

issues in the catchment. In order to achieve these objectives, the Community Catchment Plan

details a number of strategies and actions.

The C&CS Monitoring Blue-green Algae project was developed with reference to the issues

identified as part of the Catchment Plans' development, and specific actions recommended by

the Plan. These include actions to support community understanding of algal issues and

importance of catchment nutrient management. The C&CS project facilitated community

information days and produced community newsletters with the focus on explaining lakes

system ecology, and factors influencing algal blooms.

7.4.3. Specific initiatives: Dairy Industry trials to investigate effectiveness of bufferstrips

Nutrient movement from improved pasture to waterways has been identified as one of the

targeted management issues as part of the Myall Lakes Community Catchment Plan and the

LNCCMB (Lower North Coast Catchment Management Board) Integrated Catchment

Strategy. Data collected as part of the C&CS project has been used in educational material

produced to support adoption of management actions.

In the Myall River Valley, dairy production is often undertaken in conjunction with poultry

production, with manure from chicken sheds spread on pastures as fertiliser. The regular

application of manure and/or fertiliser has the potential to result in movement of nutrients

from the landscape to waterways and hence contribute to eutrophication. A number of studies

have identified the benefits to catchment water quality where vegetated buffer strips, and/or

application free buffer strips are used as part of the property management regime.

The Dungog-Gloucester Dairy Development Team has commenced a study to develop local

data to report on the effectiveness of poultry manure/fertiliser application free buffer strips.

The trial has been developed to provide benchmark data that substantiates the industry

endorsed "best management practices" to reduce potential run-off from fertiliser applications.

Run-off data collected from paddocks with/without vegetated (non application) buffer strips



identified a 25 % reduction in nutrient loading where buffer strips are used. This reiterates

that the use of buffer strips may provide a significant decrease in catchment nutrient loads.

A field day was held on one of the trial sites with summary information distributed providing

further information about the role of nutrients in estuary system health.An extract from the

information sheet produced for the Poultry Litter Field Day, organised by NSW Agriculture

and Dungog Gloucester Dairy Development team, is shown in Figure 7-3.It shows the effects

of increased nutrient loads on the functioning of a conceptualised estuary.

In healthy river and estuary systems nutrient inflows are in balanced with that of thenatural rate of processing.

Nutrient cycling in a healthy estuary system.

Increased nutrient movement from catchments can result in severe stress for riversand estuary systems with excess nutrients creating algal (plankton) blooms.



Nutrient cycling in an unhealthy estuary system.

Figure 7-3 Extract from Poultry Litter Field Day Handout (Source: DIPNR,unpublished)

7.4.4. Specific Initiatives : Upgrading of effluent management systems on the foreshores

of Myall Lakes

Myall Lakes National Park is one of the most frequently visited national parks in NSW.

Visitation generally peaks during holidays, particularly the summer and Easter holiday

periods with camping probably the most popular recreational activity within the park. For this

reason NPWS Northern Directorate developed a recreation management strategy aimed at

reserving the parks' values and attributes while providing an appropriate range of recreational

opportunities (NPWS, 2002). A major component of this strategy is the provision of minimal

facilities essential for public safety and environmental protection.

As part of the strategy toilet facilitates are provided at all major camping and picnic areas

within the park as a whole. The Myall Lakes Plan of Management (NPWS, 2002) states that

toilet facilities need to be located at camping areas with a capacity of more than five sites to

ensure that they do not impact upon groundwaters and subsequently, surface waters. The Plan

of Management also summarises the actions and guidelines for the management of the whole

park and highlights as a high priority the need to provide non-polluting toilet systems for

camping areas with a capacity of more than five sites (NPWS 2002). It goes on to also state

that visitors to small camping areas with less than five sites will be required to provide their

own self-contained toilet systems. This is to be monitored and if deemed to have unacceptable

environmental impacts toilets will be constructed.



As a result, NPWS initiated a program of replacing all existing pit toilets along the Myall

Lakes foreshore. To date facilities have been upgraded at all major camping and picnic areas

around the Lakes and have been replaced with new Gough Hybrid toilet systems (Turner

2004). This system is a wet composting toilet and is completely sealed so no effluent can

escape into the groundwater. The system consists of a series of three holding tanks, the third

of which is pumped out as required to ensure that the system is completely isolated from the

surrounding groundwater.

As these toilets have intermittent usage throughout the year a regular maintenance program

has been implemented to ensure that the tanks are operating effectively and are pumped out

when required to prevent overflow.

In addition to the facilities managed by NPWS, a commercially operated camping area exists

within the park operating under lease between the NSW Government and the lessee for the

'Myall Shores Resort Camping/Caravan Park at Bombah Point and Ferry Service'. Under the

lease Myall Shores Eco Resort operates 132 camping /caravan sites having a maximum

occupancy of 600 people on a 14 hectares site at Bombah Point.

In accordance with detailed development controls prepared by NPWS Myall Shores Eco

Resort was required to prepare a Master Plan for Myall Shores Eco Resort, which was

adopted by NPWS in 2002. The Master Plan includes comprehensive performance objectives

and detailed standards relating to operation of the park, which includes effluent disposal.

Myall Shores Eco Resort is currently implementing the Master Plan, which includes an

upgrading of toilet facilities and effluent disposal. As part of the Myall Lakes Plan of

Management NPWS have highlighted, as a high priority, the need to ensure that the

redevelopment of the Myall Shores Eco Resort complies with the approved Master Plan and

achieves the outcomes sought by NPWS for the park as a whole.



7.5. DEVELOPING PRO-ACTIVE ASSESSMENT PROTOCOLS TO ASSIST IN THEMANAGEMENT OF FUTURE ALGAL BLOOMS

An early warning of the likelihood of impending blue-green algal blooms would be very

helpful in the management of human health concerns in this system. Before this is possible a

good understanding of the conditions that allow the formation and persistence of blooms is

necessary. Sampling of parameters that have been identified as being precursors of excessive

phytoplankton growth in this system could thus provide a means of predicting the likelihood

of a bloom occurring.

As was mentioned in Section 7.1 above , and described in some detail in Chapter 4, two

distinctly different types of blue-green algal blooms have occurred in the system which

were/are initiated and moderated by quite different environmental conditions.

It is clear that the 1999 – 2000 blooms of Anabaena and Microcystis that occurred in the

Broadwater, Two-Mile and Boolambayte Lakes, was enabled by a sequence of rainfall events

that rendered the Broadwater and mid lakes very fresh. The runoff events also would have

produced nutrient laden turbid water that favoured these buoyancy regulating taxa. Under

normal (average rainfall) conditions, it appears that the water nutrient concentrations are not

elevated enough, the water clarity is reasonable, and the salinity is too high for these taxa. It

seems reasonable to conclude then, that a discrete change in conditions produced a change in

the algal community to one that favoured blue-greens over algal taxa that would otherwise be

competitively superior (Chapter 4).

It appears that this change was brought about by a period of high rainfall, but rainfall events

of similar magnitude have occurred previously. As such, this alone was not responsible for a

shift in algal community towards blue-greens. It is also highly likely that the long-term

accumulation of nutrients in the sediment may also assist in fuelling blooms following an

influx of freshwater. Subsequent monitoring of runoff events has also found that heavy

downpours facilitate the transport of disproportionately large nutrient loads in comparison to

events that deliver the same total amount of rain over a longer period. So the intensity of

rainfall could also have played a part in the 1999 bloom.

Once the toxigenic bloom was established it persisted until salinity gradually became high

enough to preclude these taxa from the phytoplankton assemblage. Apart from the catchment

rehabilitation measures mentioned in Section 7.4 there are no strategies that can prevent a

bloom of this nature becoming established, nor measures that can be taken to hasten the

decline of these blooms.



There is sound evidence that understanding the trends of changing salinity can provide an

early warning for the risk of toxigenic algal blooms which might provide some notice to the

local community of the potential loss of recreational amenity. It is therefore recommended

that long-term real time monitoring of salinity be undertaken to assist as an early warning for

the potential of a bloom occurring in the broadwater. An initial trigger of 2mS/cm or lower

conductivity would be useful initial warning system.

7.6. MYALL LAKES – WHERE TO FROM HERE?

The results of the project have identified the key characteristics, and ecological and physical

processes that contribute to the occurrence of blue-green algal blooms in Myall Lakes. This

study has provided information on the levels of temporal and spatial variation of different

parameters including water quality, nutrient concentrations, phytoplankton blooms,

macrophyte growth, and sediment characteristics. Because the project was undertaken over an

eighteen month timeframe, it effectively only represents a “snap-shot” of conditions within

the Myall Lakes. In addition, time and resource limitations has dictated that not all aspects of

the lakes biological, chemical, and physical processes could be studied in detail. As a result,

the project has also highlighted knowledge gaps that could be addressed to improve future

management of the lake and its catchment. The findings have stimulated considerable

scientific interest from other agencies, and from a number of universities.

7.6.1. Continued Monitoring in Myall Lakes and its Catchment

NPWS are committed to continue monitoring to determine the types and amount of blue-

green algae from a public health risk perspective.

The project has identified the conditions under which toxigenic algae might occur in the

lakes, and highlighted the times of year, and locations that small-celled blue-green algae

predominate. These findings have made it possible to focus monitoring to times and places

that are most likely to detect risks to public health from blue-green algae, thus ensuring a

cost-effective monitoring program. This monitoring program will consist of sampling on

reduced spatial and temporal scales to determine the composition of the phytoplankton

community, including blue-green species, and measure water quality parameters, nutrient

concentrations and water clarity.

To examine nutrient and phytoplankton responses to a rainfall event, a short-term sampling

program was initiated in December 2002 following a rainfall event of 253 mm at Bulahdelah

on the December 10th - 11th, 2002. From 12 December 2002 – 14 January 2003, an intensive

program of sampling was conducted throughout the Myall Lakes at intervals of 1, 2, 4, 6, 8,



12, 22 and 34 days after the rain event. The results of this study will be analysed to determine

the response of phytoplankton to the event.

Sampling of nutrient loads to the Broadwater during rain events will continue to be collected

by the autosampler located at Bulahdelah. In addition, DIPNR will continue to monitor

nutrient concentrations on a monthly basis in the Upper Myall River at Bulahdelah.

7.6.2. Additional ongoing investigations

Benthic Microcystis layer in Myall and Mid-Lakes: Sediment surveys during the project

revealed the presence of a highly organic layer containing a previously unknown benthic

blue-green algal species, that is closely related to the toxin-producer Microcystis. A series of

investigations additional to the project were commissioned by DIPNR to determine the

properties, toxicity and taxonomic status of this material. Ongoing studies by the University

of Newcastle, will investigate the role of this material in releasing or absorbing nutrients to, or

from, the water column. This would assist in determining its role in fuelling algal blooms,

particularly during low rainfall periods. A number of other studies by the University of NSW

and Australian Nuclear Science and Technology Organisation (ANSTO) are directed at

investigating the age and composition of the Microcystis layer and uptake of benthic

Microcystis material into the food chain through grazing. Additional work is occuring to

identify sediment biomarkers to determine whether toxigenic algal blooms have occurred

previously in the lakes.

Phytoplankton growth and nutrient limitation: It is possible that the type of nutrient (nitrogen

or phosphorus species) which stimulates phytoplankton blooms in Myall Lakes will vary

among the three lakes, and at different times depending on the prevailing environmental

conditions. Determining the type of nutrients that stimulate phytoplankton blooms is going to

be crucial to support the nutrient reduction programs in the catchment. Studies to address this

issue will be undertaken by The University of Newcastle.

Hydrodynamics of Myall Lakes: Although there is ample evidence of the strong currents

between each lake at Bombah Point and Violet Hill, there is no quantitative information on

the amount or direction of water movement between the lakes, especially after rain events.

DIPNR has collected data that will assist in determining the dynamics of water movement

between the lakes at these locations. This information will be used to support a more detailed

project by The University of Newcastle to model the hydrodynamics of the Myall Lakes.



7.6.3. Future Studies

There is still relatively little known about many aspects of physical and ecological processes

and characteristics important in maintaining the health of Myall Lakes. The topics below are a

suggested list of future studies that are likely to be of direct relevance to assessing the nutrient

status and risk of algal blooms in Myall Lakes in the short to medium term.

Determining sustainable loads of nutrients:

While the project has identified excess nutrients from the catchment as a cause of

eutrophication in Myall Lakes, and the Catchment Blueprint has identified nutrient reduction

strategies as a priority action, a quantitative target which will be effective to reduce algal

blooms has not been determined. Applying the “Sustainable Loads of Nutrients to Estuaries

Model” to Myall Lakes using information collected during the project would assist in

quantifying the load of nitrogen and phosphorus which can be delivered to Myall Lakes to

minimise the risk of damage to the health of the system. The information from this study

could be used to revise the nutrient target for Phosphrous established by the LNCCMB.

Health of Macrophytes and Seagrass:

One of the consequences of eutrophication in aquatic ecosystems is often a decline in the

distribution, biomass and health of macrophytes and seagrass. There is little quantitative

information on the growth and biomass of aquatic macrophytes in Myall Lakes. Due to the

high nutrient loads entering the Broadwater, this area is likely to be the most susceptible to

nutrient enrichment. A program to monitor the growth, biomass and condition of macrophyte

communities is required to assess the long-term health status of Myall Lakes and determine if

nutrient reduction strategies are effective.

Salinity modelling:

The risk of toxigenic algal blooms occurring in the Broadwater appears to be greatly

increased when above average rainfall delivers nutrients and reduces the salinity in the

Broadwater to less than 2mS/cm. Information on the volume of riverine inflow required to

cause these conditions, and how riverine inflow disperses throughout the lakes is needed to

develop a predictive model to determine the conditions which will increase the risk of future

blue-green algal blooms in Myall Lakes.



Sediment / nutrient fluxes:

The work undertaken by the project, as well as the earlier work undertaken by AGSO, has

highlighted the potential of nutrient fluxes from the sediment as a major internal source of

nutrients, which may also fuel blooms under certain conditions. Denitrification efficiency has

been identified as a useful tool in determining the nutrient status of a number of coastal

estuary systems. Further work on sediment / nutrient fluxes within the Myall Lakes system is

required to determine the ability of the lake’s sediment to process nutrients. Such a study

would compliment the work already underway by the University of Newcastle (see earlier).

Studies of other nutrients:

Chapter 4 provided information on algal succession in Myall Lakes, with reference to other

similar studies. Of particular interest in Myall Lakes is the role of Silica limitation in

determining algal succession and its influence on diatoms.

Groundwater:

Groundwater studies undertaken by DIPNR to determine the potential of contamination due to

onsite effluent disposal highlighted high natural background levels of nutrients in the

groundwater. At present, there is no accurate information on nutrient fluxes into and out of

the lake as a result of interactions with groundwater.

Chapter 8, References. Understanding Blue Green Algae Blooms in Myall Lakes NSW.

NSW Department of Infrastructure, Planning and Natural Resources 170

8. References.Adams , J.B., G.C. Bate and M.O. O'Callaghan. 1999. 'Primary Producers', in Estuaries of South Africa,(editors, B.R. Allanson, and D. Baird), Cambridge University Press, Cambridge.

Anderson, D.M., P.M. Gilbert and J.M. Burkholder. 2002. 'Harmful algal blooms and eutrophication:Nutrient Sources, composition, and consequences', Estuaries, 25 (4b), 704-726.

Allanson B.R., and D. Baird. 1999 Estuaries of South Africa. Cambridge University Press, UK 340p

Asaeda T., V. Kien Trung, J. Manatunge, and T. Van Bon. 2001. Modelling macrophyte-nutrient-phytoplankton interactions in shallow eutrophic lakes and the evaluation of environmental impacts.Ecological Engineering 16:341-357.

Astill, H. and P.S. Lavery. 2001. 'The Dynamics of unattached benthic macroalgal accumulations in theSwan-Canning Estuary', Hydrological Processes, 15, 2387-2399.

Atkinson, G., M. Hutchings, P. Johnson, W.D. Johnson and M.D. Melville. 1981. 'An ecologicalinvestigation of the Myall Lakes region', Australian Journal of Ecology, 6, 299-327.

Auderset Joye, D., E Castella and J. B. Lachavanne. 2002. 'Occurrence of Characeae in Switzerlandover the last tow centuries (1800-2000)', Aquatic Botany, 74, 369-385.

Australia and New Zealand Environment and Conservation Council and Agriculture and ResourceManagement Council of Australia and New Zealand (2000) Australian and New Zealand Guidelinesfor Fresh and Marine Water Quality.

Agriculture and Resource Management Council of Australia and New Zealand, 1997, Draft NationalProtocol of Monitoring of Cyanobacteria and their Toxins in Surface Waters, Based on outcomes of anational workshop held in Albury, Oct 1 1997.

Australian Geological Survey Organisation. 2000. 'Benthic Nutrient Fluxes in Bombah Broadwater,Myall Lakes', Report Number 2000/33, (editors D. Palmer, D.J. Fredericks, C. Smith, and D.T.Heggie), Department of Industry, Science and Resources Canberra.

Baginska, B.P.,. Cornish, E.S. Hollinger, G. Kuczera and D. Jones. 1998. 'Nutrients export from ruralland in Hawkesbury-Nepean Catchments', in Proceedings 9th Australian Agronomy Conference CSUWagga Wagga.

Baker, P.D. 1999. 'Role of akinetes in the development of cyanobacterial populations in the lowerMurray River, Australia', Marine and Freshwater Research, 50, 562-279.

Baker, P.D., L.D. Fabbro. 1999. A Guide to the Identification of Common Blue-Green Algae(Cyanoprokaryotes) in Australian Freshwaters, Identification Guide No.25, Cooperative ResearchCentre For Freshwater Ecology, Albury.

Blue Green Algal Taskforce 1992 Blue Green Algae, Final Report Summary, Department of WaterResources, Parramatta.

Boney, A.D. 1988. Phytoplankton, Second Edition, Edward Arnold, London 188pp.

Bornette, G., M. Guerlesquin, and C.P. Henry. 1996. 'Are the Characeae able to indicate the origin ofgroundwater in former river channels ?,' Vegetation, 125 (2), 207-222.

Boulton A.J. and M.A. Brock. 1999 Australian Freshwater Ecology: Processes and Management.Gleneagles Publishing, Glen Osmond.

Bowling, L.C. 2001. 'Notes on Algal Identification, Enumeration and Sampling', Unpublished - HunterRegion Blue-Green Algal Course Notes 14-15th May 2001, Newcastle City Hall, NSW Department ofLand and Water Conservation, Sydney.

Bowling, L.C., 1994, Occurrence and possible causes of a servere cyanobacterial bloom in LakeCargelligo, New South Wales , Australian Journal of Marine and Freshwater Research, 45, 737-745.

Bowling, L.C., and P.D. Baker. 1996. 'Major cyanobacterial bloom in the Barwon-Darling River,Australia in 1991, and underlying limnological conditions', Australian Journal of Marine &Freshwater Research, 47, 643-657.



Brierley, G.J., and K. Fryirs. 1998. 'A fluvial sediment budget for Upper Wolumla Creek, South Coast,New South Wales, Australia', Australian Geographer, 29 (1), 107-124.

Brooks, A. 1999. Lessons for river managers from the Fluvial Tardis: Direct insight into post-Europeanchannel changes from a near-intact alluvial river. In Rutherfurd, I. and Bartley, R. (Eds) Proceedings ofthe Second Australian Stream Management Conference, Vol 1, Adelaide, pp. 121-128.

Burch, M.D., and B.C. Nicholson. 2000. 'Minimisation of Cyanobacteria toxins in drinking water byreservoir management and water treatment', Proceedings, Xth World Water Congress, Melbourne, 11-17th March 2000.

Caitcheon, G., I. Prosser, D.G. Wallbrink, J. Olley, A. Hughes, G. Hancock, and A. Scott, 2001.'Sediment delivery from Moreton Bay’s main tributaries: a multifaceted approach to identifyingsediment sources', Proceedings from the Third Australian Stream Management Conference Brisbane27 -29 August 2001, (editors I. Rutherford, F. Sheldon, G. Brierley, C. Kenyon), pp 103-107.

Casanova, M.T., and M.A. Brock. 1999. 'Charophyte Occurrence, Seed Banks and Establishment inFarm Dams in New South Wales', Australian Journal of Botany, 47, 437-444.

Chorus, I. and J. Bartram. 1999. Toxic Cyanobacteria in Water: A Guide to their Public HealthConsequences, Monitoring and Management, (editors I. Chorus and J. Bartram), E & FN SpoonLondon 416 pages.

Clarke, K.R., and R.M. Warwick. 1994. Change in Marine Communities: An Approach to StatisticalAnalysis and Interpretation, 2nd Ed, Plymouth Marine Laboratories, United Kingdom.

Clarke, K.R., and R.M. Warwick. 2001. Change in Marine Communities: An Approach to StatisticalAnalysis and Interpretation, 2nd Ed, PRIMER-E: Plymouth Marine Laboratories, United Kingdom.

Dennison W.C. and E.G. Abal 1999. Moreton Bay Study: A Scientific Basis for the HealthyWaterways Campaign. South East Queensland Regional Water Quality Management Strategy,Brisbane 246p

DLWC 2002 Poultry Littler Field day Information Sheet. DLWC Hunter Region

DLWC, 2003.'Intergrated Catchment Management Plan for the Lower North Coast 2002 - Lower NorthCoast Catchment Management Board.' NSW Department of Land and Water Conservation, February2003.

DLWC. 2000. 'Hunter, Karuah & Manning Catchments State of the Rivers and Estuaries Report -2000', State of the Rivers and Estuaries Report - 2000, NSW Department of Land and WaterConservation, Sydney.

DLWC. 2000(b). 'Myall Lakes National Park Groundwater Study', (editor S.A. Realica), NSWDepartment of Land and Water Conservation, Sydney.

DLWC. In press. 'Myall Lakes Catchment Data Collation Report', (editors M.W. Dasey, and N. Cook)NSW Department of Land and Water Conservation, Sydney.

DLWC, 2000. Department of Land and Water Conservation Hunter Region Unpublished data

Entry J.A., and W.H. Emmingham. 1996. Nutrient content and extractability in riparian soilssupporting forests and grasslands. Applied Soil Ecology 4: 19-124.

Eyre B. 1997. Water quality changes in an episodically flushed sub-tropical Australian estuary: a 50year perspective. Marine Chemistry 59:177-187.

Fabbro, L.D., and L.J. Duivenvoorden. 2000. 'A two-part model linking mulitdimensionalenvironmental gradients and seasonal succession of phytoplankton assemblages', Hydrobiologia, 438,13-24.

Falconer, I.R., and A. Choice. 1992. 'Toxicity of edible mussels (Mytilus edulis) growing naturally inan estuary during a water bloom of the blue-green alga Nodularia spumigena', EnvironmentalToxicology and Water Quality: An International Journal, 7, 119-123.

Farley, T and R. Davies. 1993. Catchment Management Support System (CMSS) user manual, CSIRODivision of Water Resources, Canberra.

Fay, P. 1983. The Blue-Greens (Cyanophyta, Cyanobacteria): Studies in Biology No.160, EdwardArnold Publishing, Great Britain.



Fogg, G.E., W.D.P. Stewart, P. Fay and A.E. Walsby. 1973. The Blue Green Algae, Academic Press,London.

Gonsiorczyk T., P. Casper and R. Koschel. 1998. Phosphorus-binding forms in the sediment of anoligotrophic and eutrophic hardwater lake of the Baltic Lake district (Germany). Water Science andTechnology 37 (3): 51-58.

Gunnars, A. and S. Blomqvist. 1997. 'Phosphate exchange across the sediment-water interface whenshifting from anoxic to oxic conditions - an experimental comparison of freshwater and brackish -marine systems', Biogeochemistry, 37, 203-226.

Hallegraeff, G.M., and D.D Reid. 1986. 'Phytoplankton species succession and their hydrologicalenvironment at a coastal station off Sydney', Australian Journal of Marine and Freshwater Research37, 361-377.

Hancock, F. 1997. 'Draft nutrient management plan for the Hunter Valley - a report for the HCMT',NSW Department of Land and Water Conservation.

Harris G.P. 2001 The biogeochemistry of nitrogen and phosphorus in Australian catchments effects oflanduse and flow regulation and comparisons with global patterns. Marine and Freshwater Research52:139-149

Harris, G. P. 1999. Comparison of the biogeochemistry of lakes and estuaries: ecosystem processes,functional groups, hysteresis effects and interactions between macro- and microbiology', Marine andFreshwater Research, 50, 791-811.

Harris, G.P. 1999 (b) The response of Australian estuaries and coastal embayments to increasednutrient loading and changes in hydrology In “Australasian Estuarine Systems: Carbon, Nitrogen andPhosphorus Fluxes. (Eds: S.V. Smith and C.R.Crossland) pp 112 –24 LOICZ Reports and StudiesNo.12 (LOICZIPO: Texel, The Netherlands.

Harris, G. P. In preparation. 'Anthropogenic impacts on the ecosystems of coastal lagoons -fundamental processes and management'.

Harris, G.P. 1994. 'Pattern, process and prediction in aquatic ecology: A limnological view of somegeneral ecological problems', Freshwater Biology, 32, 143-160.

Harris, G.P., and G. Baxter. 1996. 'Interannual variability in phytoplankton biomass and speciescomposition in a subtropical reservoir', Freshwater Biology, 35, 545-560.

Hart, B.T., M. Grace, R.L. Oliver, and C. Rees. 1995. 'Nutrient cycling and algal blooms in the DarlingRiver', Researching the Barwon Darling: Proceedings of the Bourke Conference, N.S.W. 8-9th Nov1995, (editors M.C. Thoms, A. Gordon, and W. Tatnell), NSW Department of Land and WaterConservation, Sydney.

Healthy Rivers Commission of New South Wales. 2002. 'Independent Public Inquiry into CoastalLakes: Final Report', Healthy Rivers Commission, Sydney.

Hillman, K., R.J. Lukatelich, and A.J. McComb. 1990. 'The impact of nutrient enrichment on nearshoreand estuarine ecosystems in Western Australia', Proceedings of the Ecological Society of Australia, 16,39-53.

Howard-Williams, C. and M.R.M. Liptrot. 1980. 'Submerged macrophyte communities in a brackishSouth African estuarine lake system', Aquatic Botany, 9, 101-116.

Johnson, W.D., and M. Johnson. 1973. ‘Chemistry of the Myall Lakes System’, Unpublishedmanuscript, The University of New South Wales, Sydney, 11pp.

Jorgensen E.E., T.J. Canfield, and F.W. Kutz. 2000. Restored riparian buffers as tools for ecosystemrestoration in the MAIA; processes, endpoints, and measure of success for water, soil, flora and fauna.Environmental Monitoring and Assessment 63:199-210.

Krebs, C.J. 1985. 'Community Change', in Ecology - The experimental analysis of distribution andabundance, (editor C.J. Krebs), Harper and Row. New York.

Lajtha, K., and R.H Michener. 1994. Stable isotopes in ecology and environmental science. BlackwellScientific, London.



Lavery, P.S., R.J. Lukatelich, and A.J. Mc Comb. 1991. 'Changes in the biomass and speciescomposition of macroalgae in a eutrophic estuary', Estuarine, Coastal and Shelf Science, 33, 1-22.

Livingstone, R.J. 2001. Eutrophication processes in coastal systems: origin and succession of planktonblooms and effects on secondary production in Gulf Coast estuaries, CRC Press, Florida.

Lower North Coast Catchment Board. 2002. 'Integrated Catchment Plan for the Lower North Coast2002', NSW Government, Sydney.

Lukatelich, R.J., and A.J. McComb. 1986. 'Nutrient levels and the development of diatom blue-greenalgal blooms in a shallow Australian estuary', Journal of Plankton Research, 8(4), 597-618.

Mander Ü., V. Kuusemets, K.Lõhmus, and T. Mauring. 1997 Efficiency and dimendioning of riparianbuffer zones in agricultural catchments. Ecological Engineering 8: 299-324.

Manly Hydraulics Laboratory. 1998. Myall Lakes / River Water Quality Monitoring Report MHL906.NSW Public Works and Services, Sydney.

Manly Hydraulics Laboratory. 1999. 'Port Stephens/Myall Lakes Estuary Processes Study Report MHL913 January 1999', NSW Department of Public Works and Services, Sydney.

Manning/Karuah/Great Lakes Regional Algal Coordinating Committee (MKGLRACC). 2000.Manning/Karuah/Great Lakes Regional Algal Contingency Plan.

McCausland, A., P.A. Thompson, and S.I. Blackburn. 2002. 'The effect of changes in light availabilitycaused by mixing on the growth of Anabaena circinalis (Nostocales, Cyanobacteria) and Aulacoseriasp. (Centrales, Bacillariophyceae)', Phycologia, 40 (6), 530-541.

Mc Kee K.L., I.C. Feller, M. Popp and W. Wanek (2002) Mangrove iotopic (delta N-15 and delta C-13) fractionation across a nitrogen vs phosphorus limitation gradient. Ecology 83 (4): 1065-1075.

Menéndez M., and F.A. Comin. 2000. Spring and summer proliferations of floating macroalgae in aMediterranean coastal lagoon (Tancada Lagoon, Ebro Delta, NE Spain). Estuarine, Coastal and ShelfScience 51 (2): 215-226.

Mitrovic, S., and L. Bowling. 1996. Factors in the Formation of Cyanobacterial Blooms: Implicationsfor Rivers. Literature Review. Report No. TS96.089 of the Centre for Natural Resources, Departmentof Land and Water Conservation. July 1996. 48p.

Morand, P. and X. Briand. 1996. 'Excessive growth of macroalgae: A symptom of environmentaldisturbance', Botanica Marina, 39, 491-516.

Murray, A.G., and J.S. Parslow. 1999. Modelling of nutrient inputs in Port-Phillip Bay - A semi-enclosed marine Australian ecosystem', Marine and Freshwater Research, 50, 597-611.

Myall Shores Resort Manager, 2001.

Nanson, G. and C. Doyle. 1999. 'Landscape stability, quaternary climate change and Europeandegradation of coastal rivers in southeastern Australia', Proceedings from the Second Australian StreamManagement Conference Adelaide 8-11 February 1999, (editors I. Rutherford, and R. Bartley), 473-479.

National Health and Medical Research Council (NHMRC). 1994. Health Effects of ToxicCyanobacteria (Blue-Green Algae), AGPS, Canberra.

National Land and Water Resources Audit. 2001. 'National Land and Water Resources AuditWaterway and Estuarine, and Catchment Landscape Health', National Land and Water ResourcesAudit, CSIRO, University of Queensland, AGSO CRC for Coastal Zone, Estuary and WaterManagement. 25-29pp.

NPWS. 2002. 'Myall Lakes National Park & Myall Coast Reserves Plan of Management', NSWNational Parks and Wildlife Service

OECD 1982. Eutrophication of waters: Monitoring, Assessment and Control. Final Report,Organisation for Economic Co-operation and Development, Paris.

Outhet, D. 2002. 'Sediment Budget of the Myall River Catchment Reconnaissance Field Trip 16/10/02',unpublished internal report, NSW Department of Land and Water Conservation, Sydney.



Paerl, H.W. 1988. 'Growth and reproductive strategies of freshwater blue-green algae (Cyanobacteria)',in Growth and Reproductive Strategies of Freshwater Phytoplankton, (editor C.D. Sandgren),Cambridge Uni Press, New York.

Pillotto, L.S., R.M. Douglas, M.D. Burch, S. Tamarin, M. Beers, G.J. Rouch, P. Robinson, M. Kirk,C.T. Cowie, S. Hardiman, C. Moore and R.G. Attewell. 1997. 'Health effects of exposure toCyanobacteria (blue-green algae) during recreational water related activities', Australian New ZealandJournal of Public Health, 21(66), 562-571.

Rai, A.K. 1997. Cyanobacterial Nitrogen Metabolism and Environmental Biotechnology, NarosaPublications, Delhi.

Roy,P.S, R.J. Williams, A.R. Jones, I. Yassini, P.J. Gibbs, B. Coates, R.J. West, P.R. Scanes, J.P.Hudson, and S. Nichol. 2001. 'Structure and Function of South-east Australian Estuaries', EstuarineCoastal and Shelf Science, 53 (3), 351-384.

Ryan, N.J. 2002. 'An Investigation of the Factors Leading to Cyanobacteria Bloom Development andSuccession in Myall Lakes', Thesis submitted in partial fulfilment of the requirements for the GraduateDiploma in Natural Resources, University of New England, Armidale .

Ryan, N. (ed) 2000 Manning Karuah Great Lakes Regional Algal Contingency Plan, Department ofLand and Water Conservation.

Saadi, O.E., A.J. Esterman, S. Cameron, and D.M.Rodder. 1995. 'Murray River water raisedcyanobacterial cell counts and gastrointensinal and dermatological symptoms', The Medical Journal ofAustralia, 162, 122-125.

Sainty, G.R., and S.W.L. Jacobs. 1994. Waterplants in Australia, Sainty and Associates, Sydney.

Scanes P., G.Coade, D. Large, and T. Roach. 1998. Developing criteria for acceptable loads ofnutrients from catchments. Proceedings of Coastal Nutrients Workshop, October 1997, Sydney, NSW,Australia 89-99.

Sampaklis A. 2003. Nutrient content of hydrous organic sediment (gyttja) in Myall Lake and the effectsof its injection into overlying water. Honours Thesis, School of Applied Sciences, University ofNewcastle, Newcastle NSW, Australia. 100p

Scheffer M., S.H. Hosper, M.L. Meijer, B. Moss, and E. Jeppesen. 1993. Alternative equilibria inshallow lakes. Trends in Ecology and Evolution 8 (8): 275-279

Scheffer M. 1998. Ecology of Shallow Lakes. Chapman and Hall. London 357p

Schwarz, A.M., and I. Hawes. 1999. 'Mechanisms Underlying the Decline and Recovery of aCharacean Community in Fluctuating Light in a Large Oligotrophic Lake', Australian Journal ofBotany, 47, 325-336.

Skilbeck, C.G, E. Franke, A. Cramp, P. Purser and J.S. Tribble. 1999. 'A record of coastal changepreserved in high-stand littoral lakes from a stable passive margin (central eastern coast of Australia)',The non steady state of the inner shelf and shoreline: coastal change on the decades to millennia.Abstracts with Programs, Inaugural meeting of IGCP Project #437, Coastal Environmental Changeduring Sea Level Highstands, (editors C. Fletcher, and J.V. Mathews), University of Hawaii, 195 –202.

Skilbeck, C.G., T.C. Rolph, N. Hill, J. Woods and R.H. Wilkens. In press. 'HoloceneMillennial/Centennial-Scale Multi Proxy Cyclicity in Temperate Eastern Australian EstuarySediments', Submitted to Journal of Quaternary Research December 2001.

Stewart, W.D.P. 1972. 'Heterocysts of blue-green algae', in Taxonomy & Biology of Blue-Green Algae,papers submitted to the 1st Int. Symp. On Taxonomy and Biology of Blue-Green Algae, Madras 8-131970, (editor T.V. Desikachary), University of Madras.

Thom, B.G. 1965. 'Late quaternary coastal morphology of the Port Stephens-Myall Lakes Area, NSW',Journal and Proceedings, Royal Society of New South Wales, 98, 23 –36.

van der Molen D.T., R. Portielje, P.C.M. Boers, and L. Lijklema. 1998. Changes in sedimentphosphorus as a result of eutrophication and oligotrophication in Lake Veluwe, The Netherlands. WaterResearch 32 (11): 3281-3288.

Victorian Government. 1996. Blue-green algae and nutrients in Victoria - A resource Handbook,Government Of Victoria Melbourne 128 pages.



Wetzel R.G., and G.E Likens. 2000. Limnological Analyses, 3rd Edition. Springer-Verlag, New YorkWetzel & Likens, 2000 (JW)

Winder J.A., and D.M.H Cheng. 1995. ‘Quantification of Factors Controlling the development ofAnabaena circinalis blooms’, Research Report No.88, Urban Research Association of Australia,Melbourne.

Winder, J.A. 1994. 'Quantification of Factors Triggering the development of Anabaena circinalisblooms', Masters Thesis, University of Technology, Sydney

Worth, G.D. 1992. 'Some Aspects of the Sedimentology of the Broadwater, Myall Lakes, NSW', Thesissubmitted to the Department of Geography, The University of Newcastle NSW. Newcastle.

Young, W.J, F.M. Marston and R.J. Davis. 1996. 'Nutrients export and land use in AustralianCatchments', Journal of Environmental Management, 47, 165-183.

Personal Communications

Coade, G. 2002 Personal Communication NSW Environmental Protection Authority.

Harris G.P. 2002. Personal Communication 28/11/02 CSIRO Land & Water.

McKibbin, B. 2001. Personal Communication Myall Shores Resort Manager

Tuckerman, G. 2002. Personal Communication Environmental Officer, Great Lakes Council.

Turner, D. 2004. Personal Communication Myall Lakes Park Officer. NPWS Booti Booti Office.


9.1. APPENDIX 1. Groundwater quality data in Myall Lakes National Park. Concentrations in mg/L.Sample ID Site Location Date Class Type pH Water

TemperatureConductivity

? S/cmNa K Mg Ca Mn Fe NH4 F Cl Br SO4 NO3 NO2 HCO3 CO3 P SiO2 O2 N2

42980 1 The Big Gibber Quarry Jan-77 Na-Cl Groundwater 6.1 200 27 1.2 3.2 1 44 14.4

47057 2 The Big Gibber Quarry Jan-77 Na-Cl Groundwater 6.4 180 26 1.2 3.5 1.6 43 12 0.28

78017 3 Mungo Brush Aug-99 Na-Cl Groundwater 5.4 18 357 51 2.7 7 2.3 0.25 0.14 89 0.3 13 0 0 16 0 0.015

78018 4 Mungo Brush Aug-99 Na-Mg-HCO3-Cl Groundwater 5.4 17 39 5.4 0.6 1.1 0.5 0.2 0.11 7.4 < .2 0.8 0 0 15 0 0.025 0.5

78019 5 White Tree Bay Aug-99 Na-Mg-Cl-HCO3 Groundwater 5.9 16.3 416 56 3.4 12 5.3 1 0.68 95 0.3 3.4 0 0 58 0 0.05 1.1

78020 6 Broadwater Aug-99 Na-Cl Groundwater 4.1 17 121 14 0.6 1.6 0.8 0.45 0.08 25 < .2 0 0 0 0 0 0.055 0.8

78021 7 Bombah Point Aug-99 Na-Cl Groundwater 4 14.6 112 13 0.3 1.2 0.9 0.4 0.09 19 < .2 0 0 0 0 0 0.07 0.85

78022 8 Myall Shores Aug-99 Na-Mg-Cl Groundwater 5 14.9 128 17 0.7 3.8 1.4 4.9 0.1 29 < .2 0 0 0 11 0 0.035 1.4

78023 9 Myall Shores Aug-99 Na-Ca-Mg-HCO3-Cl Groundwater 6.3 17.7 97 12 1 2.8 5 2.1 0.1 7.6 0 4.3 0 0 36 0 0.015 0.45

78024 10 Korsmans Landing Aug-99 Na-Cl Groundwater 5.8 17 858 120 2.3 14 18 8.3 0.24 220 0.6 57 0 0 54 0 0.015 55

78036 11 Yagon May-00 Na-Cl-HCO3 Groundwater 6.9 18.8 766 106 5.7 14.4 10.8 0.01 180 0.7 28 0.3 0.24 86 0 0 0.24

79756 12 Mungo Point Oct-99 Na-Cl Groundwater 5.8 1575 240 8.2 31 17 0.1 4.6 0.07 0 460 1.4 0 0.02 17 0 0.015 0.5

79757 13 Bombah Point Oct-99 Na-Cl Groundwater 6.1 195 27 1.5 3.6 3.1 0 0.55 0.21 0 47 0.2 1.4 0 0.02 17 0 0.015 0.3

80300 14 Old Gibber Rd Jun-00 Na-Mg-Cl Groundwater 4 19.4 106 11 1.6 2 0.6 0.65 0.14 1 19 0.02 0.054 0.95

80301 15 River Mouth Jun-00 Na-Mg-Cl Groundwater 3.8 19 131 11 1.6 2 0.6 0 0.99 0.18 0 25 0 0.6 0 0.01 0 0 0.051 0.96

MD1 16 Myall Lake area Jul-75 Na-Cl Groundwater 6.3 200 30 1.2 3.2 0.8 52 6.7 6.03 12

MD4 17 Myall Lake area Jul-75 Na-Cl Groundwater 6.8 150 20 1 2.1 0.5 48 7 0.09 10

MD7 18 Myall Lake area Jul-75 Na-Cl Groundwater 6.5 160 22 1.1 2.4 0.8 47 6.2 0.05 10

SR1 19 Seal Rocks Sep-74 Na-Cl Groundwater 7.2 352 48 2 6 2.3 82 14 0.4 19

A 20 Upper Myall River Apr-78 Mg-Ca-Na-Cl-HCO3 River 7.7 20.8 270 15 0.7 8.5 13.8 39 13.5 0.38 60 13.7

B1 21 Upper Myall River Apr-78 Ca-Na-Mg-HCO3-Cl River 7.4 19 230 12.5 0.5 6.3 10.9 32 12 0.04 68 15.5

C1 22 Upper Myall River Apr-78 Na-Ca-Cl-HCO3 River 7.2 17.8 230 25 3.7 5 9.2 42 10.7 53 16.7

C2 23 Little Myall River Apr-78 Na-Ca-Cl-HCO3 River 7 18.2 160 18.6 3.2 2.3 11.3 31 10.8 0.02 43 19.2

L2 24 Myall River Apr-78 Na-Cl River 6.2 21.2 5200 963 38.5 125 39.5 1849 250 34 4

Ls 25 Myall River Apr-78 Na-Cl River 5.9 21.2 510 80 8.4 10.5 5.2 135 19 0.22 34 5.2

River 1 26 Crawford R. Feb-75 Na-Mg-Cl River 35 2 6.7 2.5 65 7.5 28

River 2 27 Upper Myall Feb-75 Na-Mg-Cl-HCO3 River 32 2 6.8 5 57 12.5 40

M 28 Myall River Broadwater Apr-78 Na-Cl Lake 5.7 21.6 2900 550 37.8 65 19 960 105 0.15 34 7.3

N 29 Lower Myall Broadwater Apr-78 Na-Cl Lake 6.3 21.5 5400 1080 39 126 42 1917 260 0.26 0.12 34 9

R 30 The Broadwater Apr-78 Na-Cl Lake 6.5 22.3 5300 1120 43 130 42.5 1967 284 0.12 39 8.4

S 31 Bombah Point Apr-78 Na-Cl Lake 5.3 21.6 5400 1080 44 137 43.8 1988 273 0.04 34 8.3

Mungo 32 Mungo Jul-75 Na-Cl Swamp 4.7 120 18 0.7 3 1 46 10 0.18 15

Neranie 33 Neranie 1974 Na-Cl Swamp 4.5 440 70 2.5 10 2 140 24 1 15

Scientific 34 Scientific Dec-75 Na-Cl Swamp 4.4 100 17 0.3 2.5 0.5 40 4 0.16 10

Seal Rocks 35 Seal Rocks Jul-74 Na-Cl Swamp 4.8 300 38 3.5 5 2.5 90 15 0.6 18

Smith Lake 36 Smith Lake Dec-75 Na-Cl Swamp 4.5 140 23 1.3 2.1 1 50 3.8 0.03 7

Wooli 37 Wooli Dec-75 Na-Cl Swamp 4.8 190 34 0.8 3.5 1.3 60 6.6 0.02 10

X2 38 Smith's Lake Apr-78 Na-Cl Swamp 6.6 21.6 140 21 2.4 1.8 0.1 33 8.8 0.18 15 2.7

Z 39 Bombah Point Apr-78 Na-Cl-SO4 Swamp 4.5 21.6 140 27 3.4 2.7 0.1 50 30 0.22 12 4

CSR1 40 Myall Lakes NationalPark

Jul-75 Na-Cl Runoff 6.7 100 16 2.8 1.7 2.5 33 0 2.1 11

CSR4 41 Myall Lakes NationalPark

Jul-75 Na-Cl Runoff 6.5 290 33 7 0.6 0 63 15 12.4 17

Upper Myal 42 Upper Myall 1972 Na-Cl-HCO3 Runoff 7.3 84 10 3.6 1.5 1.5 43 0 5 20

B2 43 Upper Myall River Apr-78 Na-HCO3-Cl Rain 6.4 50 2.5 1.4 0.5 0.5 5 2.2 1.3 21 0.8

Tank 1 44 Smith's Lake Feb-75 Na-Cl-HCO3 Rain 6.1 0.5 0.7 0.5 11.4 2.2 18

Tank 2 45 Upper Myall Feb-75 Na-HCO3-Cl Rain 2.6 0.5 0.45 0.8 4.7 2.4 17

X1 46 Smith's Lake Apr-78 Na-Cl-HCO3 Rain 6.9 60 5.6 0 0.5 10 2.6 0.16 11

Sea 47 World's Average Na-Cl Sea 8.1 25 10783.8 399.1 1283.7 412.1 0 6.8 19352.9 67.2 2712.4 0 0 107 16.1


9.2. APPENDIX 2

9.2.1. Theoretical assessment of toilet facilities nutrient contribution

In the assessment of the potential for tourism facilities to contribute nutrient loads to the

system, two scenarios were considered. The first is a ‘worse case’ scenario, which assumes

that all human-generated effluent, is disposed directly to the lakes. All effluent produced at

Myall Shores resort and additional waste produced by visitors to the national park were

incorporated in a direct waste input scenario. The second is a more realistic assessment based

on consideration of septic system design and incorporating a ground water contribution.

9.2.2. Assessment of tourist facilities contribution (‘worse case’).

9.2.1.1. Myall Lake National Park.

Nutrient contribution from human waste as per ‘worse case’ scenario.

Annual Park Visitors numbers 52 195 adults (average 143 day ),

Waste produced - every adult visitor’s waste directly in lake = 454 kg/N/ year; 62

kg/P/year.

With estimates derived from US EPA data. Toilet waste per adult 8.7 g N; 1.2 g P.

9.2.1.2. Myall Shores ‘Ecotourism’ resort.

Annual Occupancy assuming 400 person a day * (40 % occupancy),

146 000 visitors year, plus washing, showering et c. if directly released into lake,

Estimated nutrient generation per person of 11.2 g/N; 4 g/P per day (US EPA, 1980). The

visitors to Myall Shores are counted here as additional visitors to the National park area.

Table 9.1. ‘Worse case’ sewage input and waste-water discharge scenario.

Site Nitrogen kg / yr Phosphorus kg/yrMyall Shores 1635 584Myall Lakes National Park 454 62Total direct sewage 2089 646

Table 9.2. Comparison of ‘worse case’ input estimates with catchment loads.


Site Nitrogen kg / yr Phosphorus kg/yrTotal direct waste input 2089 646Estimate of catchment load 138400 16040

9.2.1.3. More realistic assessment of potential tourist facilities contribution

Investigation of ground water around NPWS pit toilet sites and the Myall Shores transpiration

trenches provide a more representative estimate of nutrient contribution from these sources.

These estimates were developed using high estimates of grey water production per site.

Upper estimates of grey-water produced per park visitor per day for campsites were

calculated at 51.7 L/person/day and 88 L/person/day at Myall Shores Resort area (US EPA,

1980). The following table provides an estimate of the nutrient load from facilities use in the

Myall Shores resort and Myall Lakes National Park.

Table 9.3. Estimation of potential annual nutrient load from tourism facilities.

Total Nitrogen (kg) Total Phosphorus (kg )Facilities Location

Ave. Daily Total Peak Annual Ave. Daily Total Peak Annual

Myall Shores 6.8 91.52 2345.1* 0.23 3.1 79.1

NPWS Facilities

Broadwater 0.6 81.8 278.2 0.02 2.7 9

Mungo Brush 0.2 53.2 128.5 0.02 1.6 11.3

White Tree Bay 0.3 83.1 164.7 0.03 4.9 15.8

Korsmans Landing 0.1 30.8 73.9 0.02 4.3 10.3

Total NPWS 645.3 46.4

Total TouristFacilities

340.42 2990.4 16.6 125.5

? Note 1. The Groundwater system is naturally high in Nitrogen and it is considered that measured nitrogen is acombination of groundwater plus nutrient seepage from trench (Chapter 2).

? Note 2. No faecal coliforms were detected in any ground water samples (Chapter 2).? Note 3. The AGSO Biomarker studies also found no trace of human sewerage contamination in lake

sediments.

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