nutrient assessment report balta isle car/ l/ 1003872 · 2017-10-16 · balta isle nutrient...

NUTRIENT ASSESSMENT REPORT

BALTA ISLE

CAR/ L/ 1003872

Author:

Report date: 1

Cooke Aquaculture

Scotland

Crowness Rd,

Hatston Industrial Estate,

Kirkwall,

Orkney,

KW15 1RG

T: + 44 ( 0) 1856 876101

www. cookeaqua. com

Balta Isle Nutrient Assessment Report

Table of Contents

May 17, 2017

Introduction....................................................................................................... 3

Background........................................................................................................ 4

Sitedetails......................................................................................................... 5

NutrientModelling............................................................................................ 7

ECE modelling methodology.............................................................................. 8

ECECalculations................................................................................................. 9

Results............................................................................................................. 11

Discussion........................................................................................................ 15

Mitigation........................................................................................................ 16

References....................................................................................................... 17

Cooke Aquaculture Scotland 1 17


Introduction

May 17, 2017

As part of the scoping and screening process, in relation to a proposed increase in biomass

at the Balta Isle site in Shetland, Cooke Aquaculture Scotland have carried out an

assessment of the potential water column impacts. Details of the predicted nutrient

enhancement likely to result from the discharge of the finfish site are provided as well as

taking into account any cumulative impacts from other sites in the surrounding area.

An Equilibrium Concentration Enhancement ( ECE) assessment using the semi -enclosed

water model described by Gillibrand ( 2002) will be used to assess nutrient enhancement at

the Balta Isle site.

Cumulative impacts for the area will be assessed to include all sites consented in Balta

Sound however Cooke Aquaculture Scotland proposes to relinquish all other consents in

Balta Sound to accommodate the increased biomass proposed at Balta Isle.


Balta Isle Nutrient Assessment Report May 17, 2017

Background

Fish farms release nutrients as dissolved inorganic nutrients through excretion from the fish

ammonia and phosphate), particulate organic nutrients through defecation, and dissolved

organic nutrients through resuspension from the particulate fractions. The majority of the

nitrogen ( N) wastes are released to open waters ( 68% of total) in the form of ammonia

whereas the majority of the phosphorus ( P) is accumulated in sediments ( 63%). Dissolved

inorganic nutrients are rapidly assimilated by phytoplankton and bacteria, and are then

transferred to the higher trophic levels in the planktonic food web ( Olsen and Olsen, 2008).

These nutrients can enhance the growth of marine plants and algae within the water

column. High nutrient levels may lead to algal blooms and depletion of oxygen in the water

column however it is not easy to identify the causal links of harmful algal blooms, with

impacts from fish farms on productivity yet to be demonstrated, as dilution at marine sites

is generally rapid. In the marine environment nitrogen is typically a limiting nutrient so its

addition will dictate the amount of primary production ( algal growth) however phosphorous

is not considered a limiting nutrient for phytoplankton in marine waters and therefore is of

less importance than nitrogen ( Environmental Assessment Office, 1997). The Scottish

Executive Review of environmental impacts of aquaculture concluded that the present level

of fish farming is having only a small effect on the numbers and growth rate of

phytoplankton and that this effect should not be a cause of concern except in poorly flushed

areas or areas of high farm density (Scottish Executive, 2002). It is also recognised in many

areas, especially rural areas, that nutrient inputs from agricultural land well exceeds those

from fish farming operations.

A number of steps have been taken by the industry in recent years to reduce nutrient

release into the marine environment through improvements in husbandry practices, feed

technology and feed quality, however the continuing increase in total production means

that the release of nutrients to the sea from aquaculture has also increased ( Gubbins,

2003a). Therefore monitoring nutrient levels around fish farms is important to ensuring

impacts on the water column and organisms present are reduced.



Site details

May 17, 2017

The Balta Isle fish farm is located off the west coast of the island of Balta. The development

is sited to the east side of Balta Sound, a water body which runs between the islands of Unst

and Balta. The infrastructure proposed for the site is 20 cages, 100m in circumference

arranged in two groups of 5x2 cage configurations. The north group is orientated to 3190

and the south group is orientated to 50°. Grids will be 60m2, with a net depth at the site of

7m. An increase in biomass is proposed at the site from 450 tonnes to 2, 184. 8 tonnes.

There are four fish farms including the Balta Isle site in Balta Sound which will be considered

in the cumulative assessment. If permission is granted for the proposed increase in biomass

at Balta Isle the consents for the three other sites in Balta Sound will be surrendered.

Details and locations of the four sites in Balta Sound can be found in Table 1 and Figure 1.

Table 1 Details of the fish farm sites in Balta Sound.

CAR licenceMaximum Site centre position

Distance toSite name biomass

WGS 84 NGRnumber

tonnes) Balta Isle ( km)

60o45. 065' N 465742CAR/ L/ 1003872 Balta Isle 2, 184. 8*

00047. 746' W 1208159

60045. 042' N 464800CAR/ L/ 1003067 Swarta Skerry 490 0. 94

00° 48. 783' W 1208100

60° 44. 342' N 464800CAR/ L/ 1003871 Huney 200 1. 65

00° 48. 809' W 1206800

Baltasound 60045. 374' N 463900CAR/ L/ 1003870 80 1. 92

Harbour 00° 49. 762' W 1208700

Proposed new biomass, previous consented tonnage 450 tonnes.



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Figure 1 Fish farm locations in Balta Sound.



Nutrient Modelling

Nutrient enhancement of a water body can be estimated by using two types of models. The

first is used for assessing semi -enclosed water bodies and is described by Gillibrand ( 2002).

This model is a technique used by Marine Scotland in the ' Locational Guidelines for

Authorisation of Marine Fish Farms in Scottish Waters' issued to aid marine fish farm

planning. This model is based on a semi -enclosed loch scenario with exchange of the water

body achieved through the ebbing and flooding tide to the extent that constant nutrient

input achieves a steady state concentration with tidal export and replenishment.

The second model is used for assessing sites which are not located within semi -enclosed

water bodies described by Gillibrand ( 2006) and is an alternative approach to calculating the

ECE for open water sites. Length and width of nutrient plumes are defined by parameters

extracted from hydrographic survey data where current velocities have been resolved to

along shore and across shore components. The open water model is dependent on clearly

defined tidal constituents to calculate the plume dimensions and volume on a tidal

excursion.

Hydrographic data recorded at the Balta Isle site illustrates an area not strongly influenced

by tides with relatively low current speeds and a small proportion of material ( 18%)

transported away from the site. Based on current speed analysis the site is classified as

moderately flushed, slightly quiescent and partially resuspensive. A lack of bidirectional

currents through the water column and an amplitude anisotropy value around 1 is further

evidence that there is a weak tidal influence at the site.

The Balta Isle site is located within Balta Sound which is listed as a designated area in

Marine Scotland Science ' Locational Guidelines for Authorisation of Marine Fish Farms in

Scottish Waters'. Taking into account the hydrographic data for the site and the designation

of Balta Sound by Marine Scotland Science as a semi -enclosed water body the ECE

assessment methodology described by Gillibrand ( 2002) is the most appropriate to assess

the nutrient enhancement of the Balta Isle site.



ECE modelling methodology

May 17, 2017

The ECE model is a simple box model used to predict the level of enhancement of soluble

nutrient nitrogen from fish farming sources, treating nitrogen as a conservative substance.

The model is a function of the flushing rate of a sea loch or voe, nitrogen source rate and

total consented biomass within a defined area.

The nutrient considered by the model is nitrogen, mainly in the form of dissolved ammonia

but also accounting for nitrogen emitted as particulate waste and re -dissolving into the

water column from the seabed. This is equivalent to considering that seabed conditions at

farms are generally not deteriorating with time. The combined source of nitrogen from

dissolved and particulate wastes is 48. 2kg N per tonne of salmon produced. This value is

derived from a mass balance model used to estimate the release of dissolved and

particulate nitrogenous waste from cultivated salmon ( Davies, 2000). Such an estimate is

dependent on details such as stocking, feeding and harvesting strategies employed during

cultivation. This information was derived from the records of a major salmon producer in

Scotland averaged over a large number of their on -growing sea cage sites. Total nitrogen

discharge rate is therefore the sum of the dissolved and particulate rates.

The ECE models predict the relative levels of nutrient enhancement. The results of the

model is scaled 0- 5 to give a nutrient enhancement index ( Table 2). Areas with higher ECE

values are considered to be the most environmentally sensitive to further fish farming

development due to high predicted levels of nutrient enhancement.

Table 2 Index of nutrient enhancement, derived from predicted levels of equilibrium

concentration enhancement ( ECE) for nitrogen.

Predicted ECE for nitrogenous nutrients

arising from fish farming ( µmol 1- 1)

Nutrient enhancement index

10 5

3- 10 4

1- 3 3

0. 3- 1 2

0. 3 1

0 0



ECE Calculations

May 17, 2017

The calculations used to determine the ECE values for Balta Sound using the semi -enclosed

water body model are detailed in the ' Scottish Executive Locational Guidelines for Fish

Farming: Predicted Levels of Nutrient Enhancement and Benthic Impact' ( Gillibrand, 2002).

A summary of the calculations used to assess nutrient impact are detailed below.

The flushing time of the water body can be calculated by assuming that the water volume is

replaced by the volume of water entering and leaving on each tide, the " tidal prism"

Edwards and Sharples, 1986).

Flushing time (TF) in days is calculated using the equation:

TF = 0. 52V

0. 7A. R

Where:

V is the volume of the water body (m3)

A is the surface area of the water body (m2)

R is the tidal range ( m)

The factor 0. 52 is the number of days per tidal cycle ( 1 tidal cycle = 12. 4 hours = 0. 52 days)

and the factor 0. 7 approximates the mean tidal range from the spring tidal range, R

Edwards and Sharples, 1986).

Flushing rate is calculated using the equation:

Q = 365. V

TF

The factor 365 converts the units from m3 d- 1to

m3

y-1. The flushing rate is now the total

quantity of water that is exchanged over a year.

The ECE model uses the simple equation:

ECE = S. M/ Q

Where:

M is the total consented biomass of all the finfish farms in the water body ( tonnes)

Q is the flushing rate of the water body (may1),

calculated by hydrographic characteristics

of the system

S is the source rate (total discharge of nutrient nitrogen kg tonne production)



To standardise the source rate with the calculations used in the Locational Guidelines the

nitrogen discharge of 48. 2 kg N per tonne of production is used, derived from Davies ( 2000).

The ECE units were converted from kg/m3

to µg/ I ( 1kg= 1, 000, 000µg) and then finally to µmol/

I since measurementsof dissolved nutrients are traditionally presented in these units. To

convert from µg/ I to µmol/ I the ECE value was divided by the molecular weight of nitrogen (

14g). Cooke

Aquaculture Scotland 1 17


Results

May 17, 2017

Data inputs for the ECE model have been obtained from Marine Scotland Science ' Locational

Guidelines for Authorisation of Marine Fish Farms in Scottish Waters' ( March 2017). These

include the area, volume, tidal range, flushing time and flushing rate of Balta Sound. The

production cycle for the Balta Isle site is 22 months with 2 months fallowing. To adopt a

precautionary approach and to follow the methods detailed by Gillibrand (2002) the source

of nitrogen from dissolved and particulate wastes was set at 48. 2 kg Nitrogen per tonne of

salmon produced.

The ECE modelling parameters are presented in Table 3 with Balta Sound, the Locational

Guideline area defined by Marine Scotland Science used for the ECE calculation, illustrated

in Figure 2.

Table 3 Balta Sound ECE model parameters

Area ( km2) A 3. 7

Volume of voe ( Mm3) V 30. 5

Tidal range ( m) R 1. 9

Flushing time (d) Tf 3. 3

Flushing rate ( Mm3/ yr) Q 3, 375

Nitrogen per tonne production ( kg) S 48. 2



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Figure 2 Balta Sound Locational Guideline area



As stated in Marine Scotland Science ' Locational Guidelines for Authorisation of Marine Fish

Farms in Scottish Waters' ( March 2017) a maximum biomass of 1, 220 tonnes can be

produced from the four sites in Balta Sound currently. With the increase in biomass at the

Balta Isle site this increases to 2, 954. 8 tonnes.

Three ECE modelling outputs have been reported in Table 4. The first is for the current

tonnage in Balta Sound, the second is for the proposed new tonnage to include an increase

in biomass at Balta Isle and the third is only taking into account the proposed new biomass

at Balta Isle as the other three sites consents will be revoked if the new development at

Balta Isle is approved.

Table 4 Balta Sound ECE model outputs

ECE ( 1): All sites -current tonnage

Total biomass ( t) M 1, 220

ECE ( µg/ I) 17. 42

ECE ( µmol/ I) 1. 24

Nutrient Enhancement Index 3

ECE ( 2): All sites -increased tonnage Balta Isle

Total biomass ( t) M 2, 954. 8

ECE ( µg/ I) 42. 2

ECE ( µmol/ 1) 3. 01


ECE ( 3): Balta Isle new tonnage only

Total biomass ( t) M 2, 184. 8

ECE ( µg/ 1) 31. 2

ECE ( µmol/ 1) 2. 23




The current predicted nutrient enhancement value for the Balta Sound area is 1. 24 µmol 1- 1

equivalent to a nutrient enhancement index of 3. The value is at the lower end of index

category 3 which ranges from 1 to 3 µmol/ l.

The predicted nutrient enhancement value for the Balta Sound area will increase to 3. 01

µmol 1- 1 equivalent to a nutrient enhancement index of 4, with an increase in biomass at

the Balta Isle site. The value is just within index category 4 which ranges from 3 to 10

µmol/ l.

If the new cage setup and tonnage proposed at Balta Isle is approved the licences of the

other three sites in Balta Sound will be surrendered, therefore the predicted nutrient

enhancement value for the Balta Sound area will be is 2. 23 µmol 1- 1 equivalent to a nutrient

enhancement index of 3.



Discussion

Due to the non -tidal nature of the current data recorded at the Balta Isle site and the

designation by Marine Scotland Science of Balta Sound as a semi -enclosed water body the

ECE model described by Gillibrand ( 2002) was deemed the most appropriate to assess

nutrient enhancement of the Balta Sound area.

The current predicted nutrient enhancement value for Balta Sound is 1. 24 µmol 1- 1 when

the four sites are stocked to maximum biomass ( 1, 220t), giving a nutrient enhancement

index value of 3.

When the increased biomass at Balta Isle is introduced to the area ( 2, 954. 8t) the predicted

nutrient enhancement value increases to 3. 01 µmol 1- 1 and moves the area into nutrient

enhancement category 4.

As Cooke Aquaculture Scotland propose to surrender the licences for Baltasound Harbour,

Swarta Skerry and Huney if the new development at Balta Isle is approved ( 2, 184.8t) then

the predicted nutrient enhancement value for the Balta Sound area would be 2. 23 µmol 1- 1.

This would mean Balta Sound was ranked within nutrient enhancement index category 3,

the same ranking as Balta Sound currently has.

A category 3 rating is mid -way on the nutrient enhancement index scale therefore there will

be some build- up of nutrients at the Balta Isle site however due to the location of the Balta

Isle site to the east of Balta Sound, in a strait which discharges north and south to energetic

open water it is not considered significant in terms of the current regime of the surrounding

area. With the tidal nature of the waters out with Balta Sound and the direction of transport

of material north and north east from Balta Isle, nutrients will be dispersed quickly out the

north mouth of Balta Sound.

Nutrient input to the waters around the islands of Unst and Balta from land run- off are

considered relatively low, derived primarily from agriculture notably sheep farming. There

will be some nutrient enrichment in the vicinity of the development due to nutrient release

from the fish farm, but due to the hydrographic conditions of the surrounding area it is

unlikely to lead to any environmental impacts. The majority of the effluent from the site will

be dispersed in the energetic waters to the north of the site.



Mitigation

May 17, 2017

In order to minimise nutrient input from the Balta Isle site, measures are in place to reduce

the amount of waste feed entering the water column and settling on the seabed.

Improvements in feeding efficiency and feed quality could reduce waste entering the water

column lowering the environmental impact.

The sites within Balta Sound have relatively low tonnages with none of the sites historically

producing maximum biomass during their production cycles. The Huney site has not been

used since October 2003. The three other sites have been used within the last one to two

years but have only produced collectively, approximately 50% of the maximum tonnage

505t) of the area. As the total tonnage being produced by the sites in Balta Sound is

reduced there will be lower nutrient enhancement in the area.

Monitoring will be carried out in accordance with SEPA water quality monitoring procedures

throughout the production cycle to monitor nutrients entering the water column and to act

as an early warning of a potentially harmful bloom.



References

May 17, 2017

Cooke Aquaculture Scotland ( 2016) Balta Island Hydrographic Survey Report

27/ 07/ 16)

2000). Waste production by farmed Atlantic salmon ( Salmo solar) in Scotland.

ICES CM 2000/ 0: 01, 12 pp.

Environmental Assessment Office ( 1997). Nitrogen as the limiting nutrient for

eutrophication in coastal marine ecosystems. Evolving views over three decades 1997

2006) Improving Assimilative Capacity Modelling for Scottish Coastal Waters:

II. A Model of Physical Exchange for Open Water Sites. SAMS Marine Physics Report No. 168

2002) Scottish Executive

Locational Guidelines for fish farming: predicted levels of nutrient enhancement and benthic

impact. Scottish Fisheries Research Report Number 63. FRS, Aberdeen.

2003a) OSPAR

eutrophication assessment of aquaculture hotspots in Scottish coastal waters. FRS Marine

Laboratory Collaborative Report 07/ 03, 149 pp.

Marine Scotland Science ( March 2017) Locational Guidelines for the Authorisation of Marine

Fish Farms in Scottish Waters.

2008) Environmental impact of aquaculture on coastal planktonic

ecosystems. In:

Fisheries for global welfare and environment. Proc Sth World Fisheries Congress 2008,

Terrapub, Tokyo, p 181- 196.

Scottish Executive, ( 2002). Review and Synthesis of the Environmental Impacts of

Aquaculture, The Scottish Association for Marine Science and Napier University.

2001) The significance of residual currents in the interpretation of the EU

Urban Wastewater Treatment Directive in coastal locations. Marine Pollution Bulletin, 40,

17- 21.


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