impacts of desalination on the marine ...gcdp operation began in february 2009 when elevated...

Wor World Congress/Perth Convention and Exhibition Centre (PCEC), Perth, Western Australia September 4-9, 2011 REF: IDAWC/PER11-223

IMPACTS OF DESALINATION ON THE MARINE ENVIRONMENT – SOME SIGNIFICANT BENEFITS Authors: Harry F Gordon, Paul G Viskovich, Angus L Thompson, Simon D Costanzo, Elizabeth J West, Siobhan F. E. Boerlage. Presenter: Harry F Gordon Environmental Engineer – WaterSecure – Australia Abstract The Gold Coast Seawater Desalination Plant (GCDP) was constructed in response to a prolonged drought and sustained population growth in the South East Corner of Queensland. The GCDP began construction in 2006 and operation in early 2009. The GCDP now provides a climate independent source of water to the South East Queensland Water Grid. Potential environmental impacts were identified and addressed in the design and construction of the GCDP with particular focus on the marine intake and discharge of desalination effluent (commonly referred to as brine). In accordance with regulatory approval and good environmental practice a variety of environmental marine monitoring programs were implemented in order to provide an assessment of marine impacts and benefits which could eventuate from the operation of marine seawater intake and brine outfall systems. The monitoring programs which are the focus of this paper are the Receiving Environment Monitoring Program (REMP), Entrained Organism Monitoring Program (EOMP) and an additional monitoring investigation undertaken on the diffuser and intake structures (Marine Structure Assessment). The impacts and benefits of the operation of the intake and diffuser systems have been evaluated through the collection of biological monitoring data. Based on the results of the various monitoring programs it has been concluded that the plants design features and operational procedures have ensured environmental impact upon biological parameters is minimal. Baseline monitoring of the kirra-tugun embayment indicated that the area was predominantly a featureless, gently sloping, open sand environment. The results of the monitoring programs indicate that the GCDP marine structures located within the Kirra –Tugun Embayment have provided an enhanced habitat for the settlement and recruitment of epi-benthic fauna, cryptic fauna (i.e. mobile organisms living on/under other fauna e.g. crabs) and fish communities, effectively forming an artificial reef.

IDA World Congress – Perth Convention and Exhibition Centre (PCEC), Perth, Western Australia September 4-9, 2011

REF: IDAWC/PER11-223 -2-

I. INTRODUCTION The Gold Coast Seawater Desalination Plant (GCDP) commenced construction in 2006 in response to a prolonged drought and sustained population growth and density in the South East Corner of Queensland. The GCDP was constructed in order to provide a climate independent source of water to the South East Queensland Water Grid. During the design and construction of the GCDP a number of potential environmental impacts were identified in relation to the marine intake and discharge of desalination effluent (commonly referred to as brine). The key issues which have been identified in relation to the intake and discharge are listed below:

Impingement of marine organisms (i.e. damage to marine organisms through hitting or scraping the marine intake structure).

Entrainment of marine organisms (i.e. drawing marine organisms in with plant influent). Ecotoxicity of elevated salinity brine discharge.

In order to address the issues listed above several monitoring programs were developed and implemented to gather data and assess any impacts which may be occurring. Monitoring programs have been conducted prior to and through commissioning and operational phases of the project (i.e. commencement of baseline marine monitoring was in September 2006, n.b. bethic infauna monitoring did not commence until August 2007). Commissioning of the reverse osmosis (RO) component of the GCDP commenced in November 2008 where the discharge consisted of product water and brine which had a salinity comparable to seawater. GCDP operation began in February 2009 when elevated salinity brine was first released and potable water delivered to the South East Queensland (SEQ) water grid. The purpose of this paper is to review the results of the various biological marine monitoring programs implemented for the GCDP and evaluate the apparent detrimental and beneficial impacts on the marine environment, from the first 2 years of GCDP operation (February 2009 to February 2011). II. BACKGROUND The GCDP is a seawater reverse osmosis (SWRO) plant with the capacity to produce a maximum output of 133,000 m3/d and an annual average of 125,000 m3/d of potable water. The plant has also been designed such that it can be operated at 33% and 66% of the maximum capacity. Prior to construction of the marine intake and diffuser the area was predominantly a featureless, gently sloping open sand environment. The intake system has been designed to minimise impingement and entrainment of marine organisms. The seawater intake riser is fitted with a vertical coarse-bar screen. Recognising that the intake could become a natural reef and attract fish, the riser was fitted with a dome that ensures flows are mostly horizontal rather than vertical (as fish more readily swim away from horizontal flows). The intake flow rate has been designed to limit flow to 0.05m/s at the bar screen, this velocity is one third of the 0.15 m/s considered as “best technology available” by the California Coastal Commission [1] to minimize impingement for the purpose of complying with the US Clean Water Act. With these factors combined it makes it easier for fish to swim away from the intake structure during times of intake flow and plant operation.



Figure 1: GCDP Marine Intake Structure. In addition to the measures mentioned above several other design features have been implemented into the intake structure (Figure 1) to reduce potential environmental impacts. These include the use of a copper nickel alloy for the coarse bar screens to reduce the potential for marine growth on the bars. This is one area where marine growth is less desirable as it may increase flow velocities by occluding the gap between bars. The bars are also set at a spacing of 140mm apart to allow fish easy ingress and egress from the intake structure and minimize impingement and they also have rounded edges to remove sharp angles. 2.1 Desalination Process Once onshore, influent seawater is passed through two drum screens with an aperture of 3mm. Those entrained macro-organisms greater than 3mm in size are collected from the drum screens by an automated transfer system which transfers and deposits the material within two bins. The screened intake seawater is pre-treated by conventional media filtration and coagulant (Ferric Sulphate) dosing to remove remaining particulate organic and inorganic material. The filtration system consists of 18 dual media (anthracite and sand) filters. These filters are periodically backwashed in order to maintain efficiency and remove solids; the backwash water is treated in the residuals treatment area. The solids from filter backwashing (containing residual organic matter) is thickened through settlement and centrifuging and is transferred to sludge bins for off-site disposal. The treated backwash water referred to as supernatant (turbidity of supernatant is typically



The plant has a recovery rate of approximately 40%, so that 40% of seawater entering the plant becomes pure water that is remineralised and added to the SEQ water grid. The remaining 60% is rejected by the reverse osmosis (RO) membranes as RO concentrate which is combined with supernatant to form the brine discharged from the GCDP. The brine is discharged back to the ocean in the Kirra-Tugun embayment via an underground tunnel which stretches 1.2km offshore and is discharged through an elongated diffuser system. A simplified flow diagram describes the potable water and brine production processes below (Figure 2).

Figure 2: Simplified process flow diagram for potable water and brine production.

The diffuser system consists of a central riser which evenly distributes brine to two manifold arms extending 100m in an east and west direction from the riser (Figure 3). A total of fourteen diffuser ports are located on alternating sides of the manifold arms (i.e. seven on each arm) and are oriented at 60 degrees from the horizontal plane. A small (100mm) vent centrally located on the diffuser head dome also discharges brine. The purpose of the diffuser is to dilute and disperse brine back to ambient seawater conditions within the modelled mixing zone. The size of the mixing zone during calm current conditions is based upon the modelling conducted during the design of the diffuser and is approximately 320 m long and 120 m wide and is located on the same orientation as the diffuser (i.e. 60 m from any diffuser port). During high kinetic conditions (i.e. current speed ≥ 0.5m/s) modelling predicted that the mixing zone extends up to 200 m from any diffuser port to take into account the potential for increased currents to move any high salinity plume further away from the diffuser. Figure 4 shows the location and extent of the two predicted mixing zones.

Intake Drum screens

Pre‐ treatment

Residuals

Reverse osmosis

Brine

Potable Water

Sludge

Diffuser

Process

Additive

Output

Coagulant

Filter Backwash RO Concentrate

Supernatant



Figure 3: GCDP Marine Diffuser Structure (full manifolds not shown).

As demonstrated in figure 1 and 3 the domes on the inlet riser and diffuser structure are similar in size and are located at similar depths (~18 m and 16 m, respectively).

Figure 4: Orientation and location of Predicted Mixing Zones for GCDP Operation.



2.2 Monitoring Programs In accordance with regulatory approvals the operational stage of the plant required the implementation of a variety of environmental marine monitoring programs in order to provide an assessment of marine impacts and benefits which could eventuate from the operation of marine seawater intake and brine outfall systems. The monitoring programs which are the focus of this paper are the Receiving Environment Monitoring Program (REMP), Entrained Organism Monitoring Program (EOMP) and an additional monitoring investigation undertaken on the diffuser and intake structures (Marine Structure Assessment). REMP 2.2.1 – The receiving environment monitoring program has been developed and implemented in order to satisfy the following objectives:

1. Monitor the physicochemical characteristics of the marine water in the vicinity of the discharge to ascertain whether there have been ecologically significant changes that could impact on environmental values; and

2. Detect, qualify and quantify the ecological effects of the desalination effluent and its constituent contaminants released into the receiving environment from the discharge diffuser.

The objectives of this monitoring program are achieved through a water quality monitoring and sampling program and a benthic infauna and particle size distribution (PSD) sampling program. In order to address the objectives, the evaluation of potential impacts associated with the discharge of brine from the outlet diffuser has been undertaken using marine organisms as indicators of environmental health. The release of a dense saline plume from the diffuser has the potential to impact benthic, epi-benthic and infauna (organisms living on and in the seabed). These organisms cannot readily relocate, and therefore are good indicators of impacts associated with the release of brine. The aim of the benthic infauna monitoring program is to provide an indication of whether the dense plume discharged from diffuser ports alters the abundance and community structure of the benthic infaunal community at the edge of the calm mixing zone. The aim of carrying out PSD analysis is to evaluate any potential changes in benthic habitat. The sampling of benthic infauna is undertaken at 12 sites consisting of the four sites surrounding each of the three locations (i.e. impact centre, north control and south control) used for baseline water quality monitoring. The control sites were selected as they are similar in nature to the diffuser location but far enough away to not be affected by discharges. These locations are outlined in Figure 5 below.



Figure 5: Monitoring location plan.

EOMP 2.2.2 – The entrained organism monitoring program is a continuous monitoring program developed and implemented in order to address the following objective:

Qualify and quantify the significance of the ecological effect(s) of the desalination plant’s seawater intake in regards to entrained marine organisms.

This objective is achieved through the quantification of organic matter captured at the drum screens and within the thickened sludge from the pre-treatment filter backwash treatment. Marine Structure Assessment 2.2.3 – Maintenance work carried out on the inlet and diffuser structures in mid-2010 provided an opportunity to acquire data on the floral and faunal communities that have colonised the inlet and diffuser structures after approximately 16 to 18 months of operation. This work was scoped and commissioned in order to provide an insight into the near-field (i.e. within the predicted calm mixing zone) effects of discharged brine and also the influence of the structures themselves on benthic invertebrate fauna and fishes. III. MONITORING METHODOLOGIES The monitoring programs outlined in the previous section were developed to assess the potential marine impact of the operations of the GCDP. These programs (except the marine structure assessment) were submitted for review by relevantly experienced independent third parties prior to submission and subsequent approval by the Queensland Department of Environment and Resource Management (DERM).



The activities required to carry out the monitoring programs have been outsourced to independent third party consultancy organizations. The following sections outline the methodologies employed by the contracted consultants in order to satisfy the requirements of the monitoring programs. 3.1 REMP (Benthic Infauna and PSD) Monitoring of benthic infauna has been undertaken each summer and winter around the diffuser and two reference sites over an extended period, prior to and during plant construction, commissioning and operation. The benthic infauna monitoring program is carried out in conjunction with an assessment of particle size distribution which provides information on the substrate type that characterises the habitat for infauna and plays a significant part in dictating the assemblage of organisms that inhabit the sediments. The sampling is conducted using a 0.026 m2 van Veen grab at the 12 sites as shown in figure 5 above. From each of the 12 sites, six replicate sediment samples were collected; five of the replicate samples were used for benthic infauna analysis, with the sixth used for PSD analysis. Benthic infauna samples were sieved in the field using a 1.0 mm mesh sieve. The material retained in the sieve was preserved in 4% buffered formalin (containing Bengal Rose dye) for laboratory sorting, identification and counting of organisms. The sixth sample, collected for particle size analysis, was combined and placed into a sealed plastic bag for transport to the laboratory for wet sieving to determine particle size distribution. The data collected as part of this monitoring program were statistically evaluated using a Before-After/Control-Impact (BACI), repeated-measures Analysis of Variance (ANOVA) in order to assess potential impacts of brine discharge on infauna abundance and species richness. This statistical comparison determines similarities and differences between the impact (i.e. monitoring at the edge of the calm mixing zone) and control monitoring sites both before (i.e. baseline monitoring) and after operations commenced. 3.2 Entrained Organisms Monitoring Program (EOMP) 3.2.1 Screenings - The EOMP Monitoring program has been designed and implemented to evaluate entrainment of marine organisms. In addition, video monitoring footage of the marine intake structure has been collected to monitor the level of occlusion of the inlet screen which would increase water velocity. The bins used for the collection of screenings emanating from the drum screens are located on load cells which are continuously monitored through the online monitoring system. When a sufficient volume of material is collected samples are periodically analysed to determine biomass, algal content and inorganic content. It should be noted that the entrainment rate was anticipated to be much higher during the design of the drum screen collection system. This conservative estimate has lead to design and construction of a system which is capable of handling much larger volumes than have been observed. The sizing of the transport mechanism has lead to the loss of some organic matter. Changes to system operation in July 2010 has solved some of the issues and more screenings have been observed since this work was completed. Additional works to re-align the drum screen collection chute (planned for July 2011) is anticipated to further increase the efficiency of the collection system.



Figure 6: Photograph of the Entrained Organisms Transfer System at the GCDP.

3.2.2 Sludge testing - Samples of the sludge produced in the residuals section are collected and analysed for total organic matter, total inorganic carbon, total organic carbon and total carbon, on an ad-hoc basis. Sampling and analysis of the sludge for total organic content enables the evaluation of any entrained organic matter which is not captured at the drum screens. 3.3 Marine Structure Assessment The following sections outline the methodology for the assessment of epi-benthic communities and fish assemblage around the structures. Epi-benthic Communities 3.3.1 - In order to undertake the assessment of the marine structures, a two-step approach to data gathering was employed; the first step acquired data in situ before the inlet and diffuser structures were disturbed (epi-benthic flora and fauna, and fish), and the second step acquired data once the structures were brought to the surface (cryptic fauna of the epi-benthic communities) for a final maintenance inspection. The assessment was focused primarily upon the domes located at the centre of the inlet and diffuser structures. To quantitatively measure epi-benthic flora and fauna, 72 replicate quadrats of high quality digital stills (that supported Coral Point-Count image analysis) were haphazardly taken on each dome on 18 June 2010. Epi-benthic fauna and flora coverage within each quadrat was estimated by overlaying a matrix of 75 points (distributed using a stratified random approach) on the image using image analysis software (Coral Point Count with Excel extensions (CPCe)), and taxa were identified under each of the points. Flora and fauna from each dome were identified to the lowest practical taxonomic level (generally species units; i.e. Ascidian sp. 1, Ascidian sp. 2 etc.) and into major taxonomic groups (i.e. ascidians, polychaetes etc.). Scrapings of benthic communities from the hard external surface of each of the inlet and diffuser structures were collected to examine the colonisation of epi-benthic communities, and particularly cryptic species that may have been missed in the photo quadrats. The inlet and diffuser structures



include a greater area than just the domes. However, the scraping samples were collected from the domes and main riser structures (as shown in Figures 1 and 3). There were also some differences between the inlet and diffuser structures, in that the diffuser structure was larger and more complex than the inlet structure. Samples were collected from the inlet on 8 July 2010 and from the diffuser on 5 August 2010, when the structures were removed from the water. Twenty replicate samples were haphazardly collected from the outside surfaces of each structure using a scraper to remove all material from within a 25 cm x 25 cm quadrat. Samples were placed in ziplock bags and preserved in seawater with approximately 15% methylated spirits. Samples were returned to the laboratory for examination and enumeration. All samples were stained with Rose Bengal, and macro-invertebrates were picked, sorted into morpho-species, counted and identified. Flora and fauna from each structure were identified to the lowest practical taxonomic level (generally to family) and also grouped into major taxon groups. The number of barnacles was visually estimated due to a large number of clumped individuals making individual counting unreliable. The total abundance of each taxon was recorded for each sample. For epi-benthic flora and fauna (in-situ assessment), percent cover of taxa, diversity (number of taxa per m2) and the percent cover of each major taxonomic group were calculated for each quadrat. For cryptic fauna of the epi-benthic communities (scrapings) the total density (total number of individuals per m2), taxonomic richness and abundance of each major taxon groups were calculated for each quadrat. Univariate analyses were used to detect changes between the inlet and diffuser structures. For both in-situ and scraping data, comparisons were made between inlet and diffuser structures using one-way analyses of variance (ANOVAs). Multivariate analyses consider changes to the community structure as a whole, rather than to a single component of the community (e.g. indicator species) as in univariate analyses. Multivariate analyses provide a powerful tool to determine similarities or dissimilarities in community composition (type and abundance of each taxa) among pre-determined factors (e.g. structures). Community composition was compared between structures using one-way analyses of similarity (ANOSIMs) for both in-situ and scraping data, with structures as the factor. Where required the data was transformed using standard statistical techniques for use in both the univariate and multivariate analyses.

Figure 7: A diver taking a photo during the in-situ inlet dome assessment.



Fish Communities 3.3.2 - The richness and relative abundance of fish species at each structure were assessed by underwater visual census (UVC) by scuba divers. Fish were identified in the field and photographs were taken to confirm identification where required. IV. RESULTS & DISCUSSION 4.1 Benthic In-fauna Benthic in-fauna monitoring conducted since the first baseline monitoring event in August 2007 has recorded a high degree of variability in organism abundance and diversity at both impact and reference sites over the course of the monitoring program (Figures 8 and 9, respectively). Based on these results it can be noted that abundance and diversity of infauna has shown an increasing trend since an initial decline in early 2008 prior to the commencement of GCDP operations. The outcome of the BACI repeated-measures ANOVA found that there was no significant difference (p



Figure 8: Summary of Mean Infauna Abundance and Standard Deviation (SD) (i.e. individuals per sample) Marine construction commenced July 2007.

Figure 9 : Summary of Mean Species Richness and SD (i.e. number of species per sample) Marine

construction commenced July 2007. The results of particle size distribution have been assessed to evaluate the potential impacts to benthic habitat quality for infauna. Sediment particle size measured in all monitoring events carried out since August 2007 indicate a reasonably uniform distribution dominated by sand-sized particles (0.075 mm – 2.0 mm). The measured sand content of samples throughout the sampling program has been found to range between 82% and 99%. Minor variations were, however, noted in February and August 2010 with an increase in gravel content recorded. However it should be noted that the increase in gravel content was not consistent at all sampling locations with 15.75% in February 2010 found at NC only. Results for August 2010 found 3.25% and 4.75% gravel content in samples collected at the NC and IC sites, respectively. The fraction of fine particles (silt and clay) was also found to be slightly higher at NC and IC sites during the August 2010 monitoring event (3.75% and 4.75%, respectively). Overall, the consistency in results over the monitoring period indicate a relatively stable strata distribution with minor variations observed at both impact and control locations indicating it is unlikely that the variations are the result of desalination plant operation and more likely a result of localised scouring due to the dynamic environment at the site. Longer term monitoring will provide more data which may enable further evaluation of sediment distribution trends. 4.2 Entrained Organisms Screenings 4.2.1 Results from monitoring at the intake indicate only two occasions to date where any significant mass of entrained organisms have been recorded. Based on these events the total mass of entrained organisms over the period of operation equates to approximately 110kg. Based on this figure and the total intake volume between February 2009 and February 2011 (138,000 ML) the entrainment rate is approximately 0.80g/ML. Where distinct fish or fish matter or other identifiable species (e.g. shrimp) are observed the matter is segregated and weighed separately.

0.0

5.0

10.0

15.0

20.0

25.0

Aug‐07 Feb‐08 Aug‐08 Feb‐09 Aug‐09 Feb‐10 Aug‐10

Mean species diversity/ sam

ple

Date

NC

IC

SC

Baseline Commissioning OperationMarine Construction



Sample Date

Comments

Weight kg

Lab results Test Result

May 2009 Fish 20kg Not tested N/A

1-Sep-10

Fish 91.4g Not tested N/A

Drum screen waste* 2kg Not tested N/A

9-Sep-10

Drum screen waste*

2kg

Ash (inorganic) content at

550ºC

33.70%

Organic content

66.30%

TKN as Nitrogen

23,700 mg/kg

Fish 49.5g Not tested N/A

21-Sep-10 Drum screen waste* 10kg Ash (inorganic) content at

550ºC

40.20%

Organic Content

59.80%

11-Oct-10 Drum screen waste (predominantly cornflake seaweed)

75kg Not tested N/A

Shrimp 5g 13-Oct-10 Fish 77g Not tested N/A 6-Dec-10 Fish 16.56g Not tested N/A

Table 2: Mass and analytical results for screenings collected in the drum screen system. (* Seaweed, sponge, shell etc). The drum screen waste is generally collected over a period of several days i.e. the weight indicates volumes collected between the samples dates shown above. Where possible fish or

other identifiable species (i.e. shrimp) are segregated and weighed separately. The drum screen waste transfer system was augmented in July 2010 and has since enabled more efficient and effective transfer of screenings collected from the drum screens to the bins located on the load cells. The analytical results for the sample collected in September 2010 indicates the majority of the drum screen waste (66.3%) was organic matter which was made up of fish and algal material. The remainder of the sample (33.7%) was inorganic matter (predominantly shells). Sludge Analysis 4.2.2 - Preliminary results of thickened pre-treatment sludge indicate that the sludge consists of approximately 80% moisture and the percentage of total organic carbon (TOC) ranges between 1.15% and 1.64% (the remainder is typically made up of ferric hydroxide). Based on the influent flows and sludge production rate during January and April 2010 the organic content in the influent is calculated to range between 0.83 mg/L to 0.85 mg/L. The ambient organic carbon content of seawater (measured as TOC) is typically in the range of 1.0 mg/L. Therefore based on a comparison of the sludge results with ambient seawater TOC



concentrations it suggests that the intake of seawater to the GCDP has not contributed to additional organic content entrainment.

Sludge Sample

Date

Plant Operating Capacity

Daily Sludge Production

Total Organic Content of Sludge

(TOC)

Organic Matter

Entrained Weight

Daily Influent Volume

Calculated Influent concentration of organic matter

% tonnes/day % based on lab analysis kg m3 / day mg/L

12 January 2010 66% 12.86 1.64% 211 255 000 0.83

22 April 2010 33% 14.06 1.15% 162 190 000 0.85

Table 3: Sludge analytical results and organic content evaluation 4.3 Marine Structure Assessment Epi-benthic communities 4.3.1 – For the in-situ survey, there was a much larger (statistically significant) coverage of flora (percent per quadrat), present as macroalgae, on the inlet dome compared to the diffuser dome (p < 0.05) (Figure 10). In contrast, there was a much larger (statistically significant) coverage of fauna on the diffuser dome compared to the inlet dome (p < 0.05). That is, the inlet dome was the host of more macroalgae and less sessile fauna compared to the diffuser dome. This may be a result of the different environmental conditions surrounding each of these structures such as salinity (i.e. elevated salinity surrounding the diffuser during operational periods ranges between 45 and 60 psu).

Figure 10: Mean per cent and SD of Flora and Fauna per Quadrat on the Inlet and Diffuser Structures

Identified from Coral Point Counts. Overall, there was a higher taxonomic richness of epi-benthic flora and fauna on the inlet dome compared to the diffuser dome. However, there was no statistically significant difference between the inlet and diffuser domes (p > 0.05) (Figure 11 below). Ascidians were the dominant fauna on both inlet and diffuser domes. The percent cover of ascidians on the diffuser dome was significantly greater than on the inlet dome (p < 0.05) and the percent cover of polychaetes on the inlet dome was significantly grpeater than on the diffuser dome (p < 0.05). Macroalgae were the only flora recorded and percent cover was significantly greater on the inlet dome compared to the diffuser dome (p < 0.05). Figures 11 and 12 show the mean taxonomic richness and abundance of major taxon, respectively.

010203040506070

Fauna FloraPer

cent

per

qua

drat

(%

)

Inlet



Figure 11: Mean Taxonomic Richness and (SD) on the Inlet and Diffuser Structures Identified from

Coral Point Counts.

Figure 12: Mean Abundance and SD of Major Taxon Groups on the Inlet and Diffuser Structures

Identified from Coral Point Counts. The nMDS plot shows the differences between the inlet and diffuser dome community structure, with points closer together more similar than points further apart. While there was some overlap between epi-benthic communities (measured as species units) on the inlet and diffuser domes, there was also some significant separation between the two groups (p < 0.05). The dissimilarity between domes was mainly attributed to two ascidian species, one polycheate species, green turf algae and rubble cover (substrate that is larger than sand, predominantly shell grit in this case) (See Figure 15 A). Despite similar taxonomic richness of epi-benthic communities on the inlet and diffuser domes, there were distinct differences between the structures of each community. Differences in community composition of the two structures could be attributable to the higher salinity (brine salinity ranges between 45 and 60 psu) levels surrounding the diffuser structure; alternatively, differences may also be attributed to the random nature of colonisation of species on newly submerged structures.

0

5

10

15

20

Inlet DiffuserN

umbe

r of t

axa

per

m2



For scraping samples, overall, there was a slightly higher density (number of individuals per m2) of epi-benthic communities on the diffuser structure compared to the inlet structure (refer Figure 13). However, this was not a statistically significant difference (p > 0.05).

Figure 13: Mean Total Density and SD of Epi-Benthic Communities on the Inlet and Diffuser Structures

Identified from Scrapings.

Figures 14 and 15(B) below indicate that the results for mean taxonomic richness of epi-benthic flora and fauna was slightly higher on the inlet structure compared to the diffuser structure, however this was not found to be statistically significant (p> 0.05). Polychaetes dominated (in terms of number of individuals per m2) both inlet and diffuser structure communities, and had a significantly higher density on the diffuser structure compared to the inlet structure (p < 0.05). The density of barnacles was also significantly higher on the diffuser structure (p < 0.05). In addition, the density of sponges was significantly higher on the diffuser structure compared to the inlet structure (p < 0.05). There was a clear separation of communities on the inlet and diffuser structures (p< 0.05). A large number of taxon (> 50) contributed to this dissimilarity. This included spoon worms from the class Echiura (contributed 3.2%), an unidentified bivalve sp. (contributed 2.8%), the marine gastropods Opisthobranchia (contributed 2.7%), and polychaetes from the family Flabelligeridae (contributed 2.7%). Figure 16 provides a summary of the results of scraping samples and shows the distribution of major taxonomic groups on both the inlet and diffuser structures.

0200400600800

100012001400

Inlet Diffuser

Num

ber o

f ind

ivid

uals

pe

r m2

020406080

100120140

Inlet Diffuser

Num

ber o

f tax

a pe

r m2



Figure 14: Mean Taxonomic Richness and SD of Epi-Benthic Communities on the Inlet and Diffuser Structures Identified from Scrapings.

Figure 15: nMDS plots (A): Comparing the Species Units on the Inlet and Diffuser Structures,

identified from Coral Point Counts (non transformed data) and (B): Comparing the Taxa on the Inlet and Diffuser Structures Identified from Scrapings (Note: statistical transformation of the data was required

in order to carry out this analysis). Green = Inlet Blue = Diffuser

Figure 16: Mean Abundance and SD of Major Taxon Groups on the Inlet and Diffuser Structures

Identified from Scrapings.

Fish Communities 4.3.2 -Fish assemblages associated with the underwater inlet and diffuser structures of the Gold Coast Desalination Plant comprised of species from all trophic levels, including planktivores, herbivores and invertevores. Yellowfin bream (Acanthopagrus australis), stripey (Microcanthus strigatus), big-scale parma (Parma oligolepis), woodward’s pomfret (Schuettea woodwardi) and yellowtail (Trachurus novaezelandiae) were abundant at both the inlet and diffuser



structures. Considerably fewer species were recorded in association with the inlet structure (18) than with the diffuser structure (38). The higher number of fish species at the diffuser structure is likely to reflect the greater area, diversity and complexity of physical structure that is present at the diffuser. The greater physical heterogeneity of the diffuser structure is likely to provide fish with an enhanced diversity of physical refugia from both water currents and predators. While there was no brine discharge at the time of undertaking the visual fish count, it should however, be noted that video surveillance of the marine structures has indicated a large numbers of fish congregating around the diffuser structure during times of brine discharge. V. CONCLUSIONS The biological monitoring data collected as part of the monitoring programs outlined in this paper has enabled the evaluation of the impacts and benefits of the intake and diffuser systems. Based on these results the Gold Coast Desalination Alliance have concluded that the plants design features and operational procedures have ensured environmental impact upon biological parameters is minimal. Prior to construction of the marine intake and diffuser the area was predominantly a featureless, gently sloping open sand environment. The results of the monitoring programs indicate that the marine structures located within the Kirra-Tugun embayment have provided an enhanced habitat for the settlement and recruitment of epi-benthic fauna, cryptic fauna and fish communities effectively forming artificial reefs. References:

1. Californian Coastal Commission, 2004. Seawater Desalination and the California Coastal Act 2. Gold Coast Desalination Operational Marine Monitoring Reports (Feb 2008 to January 2011).

Sinclair Knight Merz (SKM) 3. Gold Coast Desalination Plant: Inlet and Diffuser Structures: Comparison of Biodiversity and

Community Composition. (August 2010), FRC Environmental.

impacts of desalination on the marine ...gcdp operation began in february 2009 when elevated...

Documents