Development and validation of a Benthic Flux Model for the Adriatic Sea

Presenter:F. Zaffagninifabio.zaffagnini@bo.ismar.cnr.it

Zaffagnini F.1, Vichi M.1,2, Frascari F.3, Spagnoli F.4, Marcaccio M.5, Bergamini C.3

1:CMCC2:INGV3:ISMAR CNR – Bo4:ISMAR CNR – An5:ARPA ER – Bo

Keywords: Layer Model, Biogeochemistry, Diagenetic processes, Adriatic Sea

WORKSHOP W10 Progetto VECTOR(Rimini, 10-11 settembre 2007)

Geochemical Modelling:Objectives

Find homogeneous biogeochemical regions in the Adriatic Sea

Define initialization parameters for each facies

Run the simulation and compare with available observations

No predictive purposes

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Geochemical Modelling

Level Model Layer Model (BFM)Diagenetic processes: 2 approaches

Explicit depth-profile resolution

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BFM: The Layer Model

3 Layers governed by different diagenetic environments

Steady state analytical solutions are calculated (Berner equations) for each layer

Each layer considers integrated concentrations for every parameter

The evolution over time is determined through many transient solutions (Initial conditions Equilibrium)

Only vertical diffusion!

K Oxic

Suboxic

Anoxic

D1

D2

Dtot

Pelagic System

Benthic System

Berner (1980)

K1

K2

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The ModelOxic layerAnoxic layer

D Layer DepthsD(1)

D(2)

Qc(6) penetration

Qn(6) penetration

D(6)

D(7)

Qp(6) penetration

Qs(6) penetration

D(8)

D(9)

Phosphate - Oxic Layer - Dentrification Layer - Anoxic LayerNitrateAmmonium - Oxic Layer - Dentrification Layer - Anoxic LayerSilicate

K Nutrients

K(1)

K1(1)

K2(1)

K(3)

K(4)

K1(4)

K2(4)

K(5)

Organic matter flow (C,N,P,Si)

Inorganic nutrient flow (N,P,Si)

Gas exchange

(Bio)chemical reaction

Chemotrophy

Non-living OrganicCFF

Living OrganicCFF (LFG) Inorganic CFF Boundary

flow

K Inorganic speciesReduction EquivalentsK(6)

G Dissolved Gases

OxygenG(6)

Carbon dioxideG(6)

Y Zoobenthos

Yi(1)

Yi(2)

Yi(3)

Yi(4)

Yi(5)

MacrobenthosDetritivoresFilter feedersMeiobenthosInfaunal predators

Hi(1)

Hi(2)

H Benthic Bacteria

Aerobic Anaerobic

Qi(1)

Q1i(1)

Qi(6)

Q Organic Matter

Semi-ref. DOM - Oxic - AnoxicParticulate OM

Ingestion/Egestion

Respiration

Res

pira

tion

Uptake/Release

Exc

retio

n

Dissolution

Predation

Uptake/Release

Predation

Oxi

datio

n

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BFM: Output

Variations of concentration in the layers Changes of the layers’ thickness Fluxes of the major geochemical species

all outputs expressed over time

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BFM: Adriatic Seabiogeochemical facies

• 5 facies:1. High reactivity2. Medium reactivity3. Low reactivity4. Negligible reactivity5. Coastline

• First Station: S1• Many data• Most complex area• Very reactive

1

2

3 4

Frascari et al. 1997

5

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BFM: Initialization

From ISMAR – CNRdatabase (1973-2005)Sediment & pore water data:• Nutrients• DOM and POM

concentration and input• Chemical-Physical

parameters• Benthic Fluxes

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BFM: MethodInitialization of variables

Assignment of values measured in station S1

Model run

Check the evolution of variables over 10 years

Estimate the required deposition rate of Organic Matter in order to:

Maintain the initial conditionsObtain a credible equilibrium

Stationary conditions (no seasonality)Absence of feedback from the pelagic system

Numerical validity check

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BFM: InitializationChoice of the 3 layers’ thickness

Starting values

Fe in pore waterD1=0.5 cm

NO3D2=7.5 cm

Porosity POC NH3

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BFM: Results

Oxygen penetration depth Denitrification depth

Oxygen in pelagic system POC

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BFM: ResultsAmmonium

Oxic Layer

Suboxic Layer

Anoxic Layer

Phosphate

!?

Oxic Layer

Suboxic Layer

Anoxic Layer

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BFM: ConclusionsConsidering a stationary input of oxygen and organic matter,

we see: Reached equilibrium of most variables similar to startup

conditions Some variables (i.e. phosphate) show problems

Short term future purposes: Fix problems and uncertainities Add seasonality to external sources

Medium term future purposes: Apply the BFM to the other facies in Adriatic Sea Couple the BFM with the Pelagic Model

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