Modelling aquaculture impacts

choppedspleenMechanics

Feb 21, 2014 (3 years and 5 months ago)

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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 Simulator

The 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

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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 INFORMATION THROUGH MERAMOD
MERAMOD MODULES (I)
GRID GENERATION MODULE
INPUT

CAGE POSITIONS

STATION POSITIONS

BATHYMETRY
INPUT

CAGE POSITIONS

STATION POSITIONS

BATHYMETRY
INPUT

CAGE POSITIONS

STATION POSITIONS

BATHYMETRY
water
column
sea surface
GRID GENERATION MODULE
INPUT

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 RESUSPENSION
MODEL PARAMETERS
(e.g. critical resuspension, deposition
shear stress; erodibility constant)
INPUT

VALIDATED RESUSPENSION
MODEL PARAMETERS
(e.g. critical resuspension, deposition
shear stress; erodibility constant)
INPUT

VALIDATED RESUSPENSION
MODEL PARAMETERS
(e.g. critical resuspension, deposition
shear stress; erodibility constant)
BENTHIC MODULE

BENTHIC COMMUNITY
SUCCESSION LINKED TO
QUANTITATIVE INPUTS OF
SOLIDS
BENTHIC MODULE

BENTHIC COMMUNITY
SUCCESSION LINKED TO
QUANTITATIVE INPUTS OF
SOLIDS
carbon/ solids
accumulation
g m
-
2
yr
-
1
underlying
sediment
layer
bed surface
water
column
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/ solids
accumulation
g m
-
2
yr
-
1
underlying
sediment
layer
bed surface
water
column
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)

75 cm

H:D =
5:1 ratio

x6 or x12

x6

x6

Upper (U)

Lower (L)

Water column
(WC)

1. Deploy

2. Retrieve, filter, dry

3. Calculate observed flux

(total waste particulate
material = g solids m
-
2

yr
-
1
)

4. Check calculation




Typical impact footprints


Dispersive sites

Strong currents

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

Typical of fish farms in Scotland


Depositional sites

Weaker currents

Impact over a limited area (up to 30 m)

But more intense

Typical of farms in Greece

R
2
= 0.82
0
20
40
60
80
100
120
140
160
1
10
100
1000
10000
100000
Species (no. m
-2
)
R
2
= 0.96
R
2
= 0.7454
0
20
40
60
80
100
120
140
160
1
10
100
1000
10000
100000
Species (no. m
-2
)
1MD4
1MD5
R
2
= 0.52
1000
10000
100000
1000000
1
10
100
1000
10000
100000
Abundance (Ind. m
-2
)
1000
10000
100000
1000000
1
10
100
1000
10000
100000
Abundance (Ind. m
-2
)
1
10
100
1000
1
10
100
1000
10000
100000
Modelled flux + 1 (g m
-2
yr
-1
)
Biomass (g m
-2
)
1
10
100
1000
10000
1
10
100
1000
10000
100000
Modelled flux + 1 (g m
-2
yr
-1
)
Biomass (g m
-2
)
Species



Abundance

Modelled flux (g m
-
2

yr
-
1
)

R
2
= 0.48
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
1
10
100
1000
10000
100000
A/S
0.0
500.0
1000.0
1500.0
2000.0
2500.0
3000.0
3500.0
4000.0
1
10
100
1000
10000
100000
A/S
1MD4
1MD5
R
2
= 0.71
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
1
10
100
1000
10000
100000
H'
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
1
10
100
1000
10000
100000
H'
R
2
= 0.37
-200
-100
0
100
200
300
400
1
10
100
1000
10000
100000
Modelled flux (g m
-2
yr
-1
)
Eh (4 cm)
-250
-200
-150
-100
-50
0
50
100
1
10
100
1000
10000
100000
Modelled flux (g m
-2
yr
-1
)
Eh (4 cm)
R
2
= 0.26
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1
10
100
1000
10000
100000
Simpson
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1
10
100
1000
10000
100000
Simpson
Model
validation

Shannon Weiner

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


Use of models in knowledge transfer

100
150
200
250
300
350
400
2
0
0
2
5
0
3
0
0
3
5
0
4
0
0
4
5
0
0A
5A
10A
25A
50A
N
a. tightly clustered (square)
b. largely spaced out (circular)
Solids flux (g m yr )
-2 -1
100 m
0
100
200
300
400
500
600
Easting (m)
0
1
0
0
2
0
0
3
0
0
4
0
0
5
0
0
6
0
0
N
o
r
t
h
i
n
g

(
m
)
0A
5A
10A
25A
50A
500
2500
5000
10000
30000
Closely spaced cages

Largely spaced

Sedimentation


4 cages weak current

200
300
400
500
600
700
800
4 cages CM10
200
300
400
500
600
700
800
500
1000
2000
3000
4000
5000
6000
8000
10000
14000
18000
Sensitive
habitats

Sedimentation


4 cages strong current

200
300
400
500
600
700
800
4 cages CM06
200
300
400
500
600
700
800
500
1000
2000
3000
4000
5000
6000
Sensitive
habitats