Modelling aquaculture impacts

MOM (Modelling - Ongrowing fish farms - Monitoring)This model developed in Norway is a three component model for

modelling organic impacts.The fish sub-model simulates the release of particulate material from

the farm based on information on the feeding rate and composition of food. Uptake, retention and excretion are all calculated in relation to the temperature and size of the fish.

The output from this sub-model provides the initial conditions for the dispersion sub-model which simulates dispersion and sedimentation rates of excess feed and faecal pellets.

The sediment sub-model calculates the maximum decomposition at the seabed for a particular scenario and oxygen concentration in the benthic boundary layer is also calculated.

The combination of these sub-models allows the calculation of maximum fish production that a site can sustain without adverse benthic effects.

AWATS - Aquaculture Waste Transport SimulatorThe AWATS model is a mathematical model to simulate

tidal and wind-driven currents, waves, and the resulting dispersion of fish food and faecal matter in coastal areas.

This model was one of the first aquaculture organic impact models to include complex models of the descriptions of spatially varying current around the study area.

In addition, wind driven flow and waves are also included as processes having an effect on the subsequent dispersal of discharged particulate material.

This model originally lacked resuspension which causes deposited particles to be re-entrained into near bed flows and advected away from the initial footprint area.

DEPOMOD

This model is a lagrangian particle tracking model which predicts the dispersion of particulate wastes arising from aquaculture activities and associated benthic impacts.

It was developed from a sewage dispersion model also developed by SAMS, but required extensive modification to data input requirements and validation for the fish farming environment.

There are three main modules: • particle tracking, • resuspension • benthic response. Predictions of solids accumulation (g m-2 yr-1) determine

the benthic response using a relationship between solids accumulation and benthic indices validated for Scottish fish farms.

Current profiles in stratified waters are complex. Particles settling at different rates are subject to current shear and turbulence

0 C u rre n t V e lo c ity

S ou rce

C o a rse M ed iu m

F in e

MERAMOD

• Is a conversion of Depomod from cols water areas to temperate areas

• There is an addition of wild fish component to take into account the utilisation of waste feed by wild fish under the cages

• It also takes into account the different species and behaviour of faecal pellets in the water column.

• It is validated for cage farms in the Mediterranean

FLOW OF IN FORM ATION THROUGH M ERAM OD

MERAMOD MODULES (I)

GRID GENERATION MODULEINPUT• CAGE POSITIONS• STATION POSITIONS• BATHYMETRY

INPUT• CAGE POSITIONS• STATION POSITIONS• BATHYMETRY

INPUT• CAGE POSITIONS• STATION POSITIONS• BATHYMETRY

watercolumn

sea surface

GRID GENERATION MODULEINPUT

•CAGE POSITIONS

•STATION POSITIONS

•BATHYMETRY

PARTICLE TRACKING MODULE

•DIFFERENTIAL SETTLING OF PARTICLES

• ADVECTION OF PARTICLES BY CURRENTS

• REPRESENTATION OF CURRENT SHEAR

• TURBULENCE (RANDOM WALK)

WILD FISH MODULE•Input pelagic/ benthic feeding

effects by wild fish

sea surface

INPUT

•FEED INPUT/ SPECIES CAGE BY

CAGE; HYDROGRAPHIC DATA;

SETTLING VELOCITY DATA

•VARYING LEVELS OF

SCENARIO COMPLEXITY

MERAMOD modules (I)

MERAMOD MODULES (II)

INPUT

• VALIDATED RESUSPENSIONMODEL PARAMETERS

(e.g. critical resuspension, depositionshear stress; erodibility constant)

INPUT

• VALIDATED RESUSPENSIONMODEL PARAMETERS

(e.g. critical resuspension, depositionshear stress; erodibility constant)

INPUT

• VALIDATED RESUSPENSIONMODEL PARAMETERS

(e.g. critical resuspension, depositionshear stress; erodibility constant)

BENTHIC MODULE

• BENTHIC COMMUNITYSUCCESSION LINKED TO QUANTITATIVE INPUTS OFSOLIDS

BENTHIC MODULE

• BENTHIC COMMUNITYSUCCESSION LINKED TO QUANTITATIVE INPUTS OFSOLIDS

carbon/ solidsaccumulationg m-2 yr-1

underlyingsedimentlayer

bed surface

watercolumn

RESUSPENSION & CARBON DEGRADATION

• RESUSPENSION FROM BED

• CARBON DEGRADATION - G MODEL

RESUSPENSION & CARBON DEGRADATION

• RESUSPENSION FROM BED

• CARBON DEGRADATION - G MODEL

BENTHIC MODULE• BENTHIC COMMUNITY SUCCESSION LINKED

TO QUANTITATIVE INPUTS OF SOLIDS carbon/ solidsaccumulationg m-2 yr-1

underlyingsedimentlayer

bed surface

watercolumn

FLUX/DEPOSITION MODULE• FLUX/ DEPOSITION ON BED

• CARBON DEGRADATION - G MODEL

MERAMOD modules (II)

Crucial input data for modelling

There are a number of key input data issues which need to be addressed when developing an existing model for application in a different environment. Although the principal physical processes can be applied to different areas, the input data used to drive these components need to be critically assessed.

Sediment trap experiments (model validation)Sediment trap experiments (model validation)

75 cm

H:D = 5:1 ratio

x6 or x12x6x6

Upper (U) Lower (L)Water column

(WC)

1. Deploy2. Retrieve, filter, dry3. Calculate observed flux(total waste particulate material = g solids m-2 yr-1)4. Check calculation

Typical impact footprints

Dispersive sitesStrong currents

Impact over a larger area (up to 100 m) but less intense

Typical of fish farms in Scotland

Depositional sitesWeaker currents

Impact over a limited area (up to 30 m)

But more intense

Typical of farms in Greece

R2 = 0.82

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110100100010000100000

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. m-2

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020406080100120140160

110100100010000100000

R2 = 0.52

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bund

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Species

Abundance

Modelled flux (g m-2 yr-1)

020004000600080001000012000140001600018000

110100100010000100000

R2 = 0.71

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110100100010000100000

Model Model validationvalidation

Shannon Weiner

Use benthic data to establish relationships between benthic indices and flux predictions

Use of models in knowledge transfer

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0 A5 A1 0 A2 5 A

5 0 A

N

a . t i g h t l y c l u s t e r e d ( s q u a r e )b . l a r g e l y s p a c e d o u t ( c i r c u l a r )

S o l i d s f l u x ( g m y r )-2 -1

100 m

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Easting (m )

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Closely spaced cages Largely spaced

Sedimentation – 4 cages weak current

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4 cages C M 10

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Sensitive habitats