modelling the impact of finfish aquaculture on sediment...

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MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRY Daniele Brigolin, University of Venice ECEM 2007, Trieste November 27-30 Pastres Roberto University of Venice, Italy EU FP6 ECASA project www.ecasa.org.uk Chris Cromey, T.D. Nickell SAMS, Oban, Scotland (UK) D.R. Aguilera, Pierre Regnier University of Utrecht, The Netherlands

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Page 1: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT

BIOGEOCHEMISTRYDaniele Brigolin, University of Venice

ECEM 2007, Trieste November 27-30

Pastres Roberto University of Venice, Italy

EU FP6 ECASA projectwww.ecasa.org.uk

Chris Cromey, T.D. Nickell SAMS, Oban, Scotland (UK)

D.R. Aguilera, Pierre Regnier University of Utrecht, The Netherlands

Page 2: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Outline

• Impacts of finfish farming on the sediment geochemistry;

• Description of the model;

• Study site and field data description;

• Results of model calibration;

• Response of model output to the establishment of a new salmon farm;

• Perspectives.

Page 3: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Finfish farming impacts on the sediment

Potential impacts on the sediment (e.g. Hargrave et al., 1997; Pearson & Black, 2000)

currents

Wasted food

sedimentation

burial

Oxic and anoxic mineralization

Faeces

S=, NH4+, DIP

Increase in the superficial OC concentration

Decrease of the oxygen penetration depth

Increase in dissolved nutrient concentrations

Increase in S= concentrations

Changes in macrofaunal community

Changes in the fluxes at the sediment-water interface

Changes in the chemical properties of the sediments provide a measure of the impact caused by the fish farm which is integrated over time.

Benthic impacts are proportional to:

Exposure of the site (currents);

Husbandry practices (feeding strategy and quality of the food)

Page 4: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Modelling the impacts of finfish farming on the sediments

OC flux reaching the sediment-water interface

Bioticindexes (ITI, AMBI)

Simple geochemicalindicators (TOC)

Current approach

OC flux reaching the sediment-water interface

Ecologicalindexes

Approach proposed in this work

More complex geochemical indicators (e.g. NH4

+, S=, O2..)

Page 5: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Conceptual model: Deposition + Early diagenesis

WATERCOLUMN

Food wastage and Faeces production

Deposition model(DEPOMODTM)

Organic carbon flux

Current velocity

O2 demand, nutrient fluxes

EDM: Early Diagenetic ModelEDM: Early Diagenetic Model(developed in BRNS(developed in BRNSTM TM environment)environment)

SedimenttemperatureSEDIMENT

DEPOMOD – particle tracking model (Cromey et al., 2002 Aquaculture)

(validated for Scottish sealochs)

Page 6: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Objectives of this work

1) evaluating the applicability of a Reactive-Transport Model of early diagenesis (EDM) in combination with the DEPOMOD;

2) testing DEPOMOD+EDM integrated model at sites which are exposed to high organic carbon fluxes from aquaculture activities, under transient conditions.

The potential use of the integrated model is discussed in relation to benthic biogeochemical indicators for cost-effective EIA and monitoring practices.

Page 7: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Surficial sediment

layer

Deep sediment layer

Water column

Temp. Fluxes:

OC, Fe(III), Mn(IV)

Lower boundary condition: null gradient

t: time z: depthΣR variation in the concentration due to biogeochemical processesDB diffusion coefficientω : sedimentation rateφ: sediment porosity.

The modeller specifies the fluxes at the upper boundary for the solid species, and the concentrations for the dissolved speciesConcentr.:

O2, NH4+, HPO4

2-, NO3-,

SO42-, Mn2+, Fe2+

( ) ( ) ( ) ( )( )t,,CRzCD

zzC

tC

ssBss βϕϕωϕϕ −+

∂−∂

∂∂+

∂−∂−=

∂−∂ 1111

( ) ( )t,,CRz

Cln/DzCD

zzC

tC

wwmwBww βϕϕϕϕϕ ωϕ +

∂−∂+

∂∂

∂∂+

∂∂−=

∂∂ 21

Organic matter degradation and early diagenesis processes: conceptual model

Page 8: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Surficial sediment

layer

Deep sediment layer

Water column

Temp. Fluxes:

OC, Fe(III), Mn(IV)

Lower boundary condition: null gradient

t: time z: depthΣR variation in the concentration due to biogeochemical processesDB diffusion coefficientω : sedimentation rateφ: sediment porosity.

The modeller specifies the fluxes at the upper boundary for the solid species, and the concentrations for the dissolved speciesConcentr.:

O2, NH4+, HPO4

2-, NO3-,

SO42-, Mn2+, Fe2+

( ) ( ) ( ) ( )( )t,,CRzCD

zzC

tC

ssBss βϕϕωϕϕ −+

∂−∂

∂∂+

∂−∂−=

∂−∂ 1111

( ) ( )t,,CRz

Cln/DzCD

zzC

tC

wwmwBww βϕϕϕϕϕ ωϕ +

∂−∂+

∂∂

∂∂+

∂∂−=

∂∂ 21

Organic matter degradation and early diagenesis processes: conceptual model

Operator splitting methodImplicit Numerical scheme

Regnier et al. (2002) Appl. Math. Model.

Page 9: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Organic Matter

Organic matter Degradation

redox reactions

Electron acceptors:O2, NO3

-, Fe(III)Mn(IV), SO42-

Re-oxidationreactions

Reduced compoundsFe2+, Mn2+, NH4

+, S=

Electron acceptorsO2, Fe(III),

Mn(IV)

FeS & Carbonates Precipitations

Carbonates equilibria

Fluxes of NH4+, O2, DIP

BRNS Early diagenesis model Reaction network: Primary & Secondary reactions

Sediment Water Interface

Page 10: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

A purposely-designed field campaign was carried out in August 2006, in order to apply the integrated model

The fish-farm wasmoved to the actualsite in Feb 2006

Study site – Loch Creran, West coast of Scotland

Page 11: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Study site – Loch Creran, West coast of Scotland

3 stations : 10m and 40m from the cages, and control;

3 replicates per station using a megacorer (Φ =100 mm);

Analysis were performed at each 1 cm on the top 10 cm + surnatant waters.

Parameters sampled:

- Porosity;- Organic Carbon in the sediment;- Fe2+ and Mn2+ in pore waters;- NH4

+ and HPO42- in pore waters;

- SO42- in pore waters.

Page 12: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Application of the model at Loch Creran - methodology

Step 1: the Early Diagenesis Model (EDM) was calibrated, by comparing the steady-state model outputs with the field data collected at station BC (control);

Step 2: the DEPOMOD was run, in order to obtain a prediction of the farm originated Organic Carbon flux at stations B10 and B40;

Step 3: organic carbon fluxes predicted by DEPOMOD are added to the background OC fluxes, moving the EDM from a steady-state to a transient-state;

Step 4: transient profiles predicted by the model are compared with a set of sediment chemistry data purposely collected at stations B10 and B40.

Page 13: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Step 1, results: EDM calibration – station Bc

- All the parameters of the model were fixed on the basis of literature references;

- The fluxes of solids OC, Fe(III) and Mn(IV) at the upper boundary were calibrated by minimizing a goal function which quantifies the deviation between model predictions and field data.

0 1 2 3 4OC [%]

0

5

10

dept

h [c

m]

a

0 100 200 300 400NH+

4 [µ mol L-1]

0

5

10

dept

h [c

m]

b

0 40 80DIP [µ mol L-1]

0

5

10

dept

h [c

m]

c

0 20 40SO4 [mmol L-1]

0

5

10

dept

h [c

m]

d

0 40 80 120 160 200Fe2+

[µ mol L-1]

0

5

10

dept

h [c

m]

e

0 40 80 120Mn2+

[µ mol L-1]

0

5

10

dept

h [c

m]

f

Page 14: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Step 2: DEPOMOD output – organic carbon flux at the S.W.I.

500

1000

1500

2000

Salmon cagesSampling stations

g C m-2 yr-1

B40

B10

50m

50m 500

1000

1500

2000

Salmon cagesSampling stations

g C m-2 yr-1

B40

B10

500

1000

1500

2000

Salmon cagesSampling stations

g C m-2 yr-1

B40

B10

50m

50m

At the time of the survey,the fish-farm has beenoperating for 6 months.

Production: 1500 tonn y-1

6 x 22m Φ circular net cages reaching 14m depth

5% of feed waste was assumed;

Farm details:

Page 15: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Step 3: EDM transient simulation

OC (food+faeces) flux at Station B10

Depomod output

These fluxes were added on the top of the background OC flux, which was estimated by calibrating the EDM.

This additional OC flux was imposed for 6 months (age of the farm), perturbing the steady-state profiles and driving the model to a transient-state.

Page 16: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Step 4. EDM model output vs field data at station B10

- Due to the mineralization of elevated quantities of fish farm-derived labile organic matter, nutrient concentrations at station B10 are greatly enhanced compared with the non-impacted station BC, reaching values approximately 10 times higher

- A sub-surface maximum in nutrient concentration is localized around 5 cm depth

0 4 8OC [%]

0

5

10

dept

h [c

m]

a

0 1000 2000 3000 4000NH+

4 [µ mol L-1]

0

5

10

dept

h [c

m]

b

0 400 800DIP [µ mol L-1]

0

5

10

dept

h [c

m]

c

0 20 40SO4 [mmol L-1]

0

5

10

dept

h [c

m]

d

0 40 80 120 160 200Fe2+

[µ mol L-1]

0

5

10

dept

h [c

m]

e

0 40 80 120Mn2+

[µ mol L-1]

0

5

10

dept

h [c

m]

f

Page 17: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Model predicted fluxes at the sediment-water interface

NH4 efflux mmol m-2 d-1

0.00

5.00

10.00

15.00

Bc B10

The model predicts a relevant enhancement in NH4+ efflux at the station

localized underneath the farm, with respect to the control station.

NH4 efflux and sediment oxygen demand, are predicted by the model.

Page 18: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

0.0 4.0 8.0 12.0 16.0 20.0S(-II) [mmol L-1]

0

5

10

dept

h [c

m]

5% waste

2% waste

0 1000 2000 3000 4000NH+

4 [µ mol L-1]

0

5

10

dept

h [c

m]

5% waste

2% waste

Perspectives – Farm management practices

In order to test the integrated model sensitivity to boundary conditions, a scenario was run by assuming a lower percentage of fish food wasted, 2% instead of 5%,

These results indicate that the integrated model may represent an useful tool for studying the level of impact on sediment geochemistry associated with different management practices.

Page 19: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Perspectives - Prediction of cost-effective indicators

0.0 4.0 8.0 12.0 16.0 20.0S(-II) [mmol L-1]

0

5

10

dept

h [c

m]

The future aim of this class of models might typically be to focus on the prediction of cost-effective indicators of organic enrichment.

According to Hargrave et al. (1997) S = concentration and sediment oxygen demand are among the most sensitive indicators of fish-farm organic enrichement.

The current efforts to provide in situ monitoring of sediment ecosystems (e.g. www.cobo.org.uk) are improving the suitability of this class of geochemical-based measures.

Wildish et al. (2001) concluded that monitoring programs based on geochemical measures are more cost-effective than the ones based on macrofaunal community measures.

Page 20: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Concluding remarks

Two numerical models, simulating fish-farm waste deposition and early diagenesis processes in the sediment, were applied at a Fjordic Sealoch, for studying the impacts of finfish aquaculture on sedimentary redox dynamics.

The early diagenesis model (EDM) was calibrated by using a set of original field data of selected pore water and solid-state chemical species measured in the field at a pristine site.

The EDM response to an increase in OC rain due to the installation of the fish farm was studied by comparing model predictions with field data.

The study of the EDM behaviour under transient conditions and the potential use of the two integrated models for aquaculture site-selection and monitoring purposes were the most relevant aspects discussed in this work.

Page 21: MODELLING THE IMPACT OF FINFISH AQUACULTURE ON SEDIMENT BIOGEOCHEMISTRYdoga.ogs.trieste.it/.../ecem07/RoomC/29Nov/Brigolin_D.pdf · 2007-12-12 · MODELLING THE IMPACT OF FINFISH

Thank you !

The authors gratefully acknowledge the assistance of Ms Susan McKinlay with core slicing, Mrs Heather Orr with CHN analysis, Ms Cheryl Haidon with metals analysis, Mr Tim Brand for phosphate analysis and Mr Martyn Harvey with sulphate analysis