Nutrient Dynamics in Estuarine and Coastal Marine Ecosystems

Daniel Conley1, Peter M.J. Herman2 and Vincent Escaravage2

1Department of Marine Ecology, National Environmental Research Institute, Roskilde, Denmark and Department of Marine Ecology, Institute of Biological Sciences, University of Aarhus, Denmark

2Netherlands Institute of Ecology, Centre for Estuarine and Marine Ecology, The Netherlands

Why nutrients?

Introduction

Significant advances within the last 2 decades ELOISE, LMER/LTER, LOICZ, National

Nutrient inputs

Sources, quantification, ratios, time

Coastal zone as an active transformer of nutrients

N, P, Si, limitation and eutrophication

Final thoughts

Wade et al. 2002

Modelling N transfer from catchments to estuaries using deterministic models

Integrated Nitrogen Model for European catchments (INCA)

Smith et al. 1997

Modelling N transfer: SPARROWSPAtially Referenced Regressions On Watershed Attributes

Empirically derived estimates from in stream measurements

Estimated nitrogen export (kg/km2/yr)

Alexander et al. 2000

A rapid decline in the rate of nitrogen loss with channel size

Proximity of sources to large streams and rivers is a major determinant of N transport

Billen and Garnier 2002

River Strahler Model Complex

Garnier et al. 2002

Ratios of inputs of N, P and Si have changed with time

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N-DIN

N-DIN

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DSi

DSi

River Strahler applied to the Danube for periods 1988-91 and 1994-95 Nitrogen loading reductions

Large reductions in phosphorus loading

Formulations for Si are primitive

Long-term changes in DSi transport from building of dams, eutrophication of lakes, and land-use practices

De Leeuw et al. 2002

Modelling atmospheric nitrogen depositionDe Leeuw et al., 2003

30% of N loading from atmospheric deposition

Wet deposition represents 81% of N deposition

Identify sources of N

But…

Needs improved temporal and spatial resolution

P deposition?

ANICE and MEAD projects

Buddemeier 1997

SCOR/LOICZ Working Group onground water inputs

Estimates of groundwater fluxes are necessary for nutrient budgets

Important, but fluxes are notoriously uncertain

Harmonized Procedures for quantificationof nutrient losses from diffuse sources (HARP)

Developing harmonized modelling tools for integrated basin management

Darracq and Destouni 2004

Model assumptions influences final result

Used different spatial process and parameter aggregation procedures

Figure a - A 50% N reduction could be achieved by focusing on eastern basin

Figures b and c predict that reductions should be spread over entire basin

Economic and societal consequences

What about nutrient loading in the past?

Clarke et al. 2003

Monitoring Long-term Trends in Eutrophication and Nutrients in the Coastal Zone (MOLTEN)

TNincreasedfrom ca.

45 to 90 Min the last50 years

Bradshaw and Rasmussen 2004

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Dallund Sæ, Denmark

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TN

Planktonic Benthic

µmol l-1

Active area of research and development

Summary of land side

Importance for management, e.g. WFD

Need for scenarios

Models, models and more models

Risgaard-Petersen 2003

Significant advances in our understanding of the nitrogen cycle

Sediment microalgae are strong competitors for nitrogen

Strongly reduced denitrification in autotrophic sediments

Seagrass communities also play an important role in N transformations

NH4+ + NO2

- = N2 + H2OKnown to occur in WWTP

Discovery of anaerobic ammonium oxidation (ANAMMOX) in the marine

environment

Accounts for up to 65% of N2

production on shelf sediments

ANAMMOX is responsible for a significant part of the global N2 production (25-50 %)

Dalsgaard et al. 2003

Stedmon et al. 2004

Cycling of Dissolved Organic Nitrogen (DON)

DON 12%PON 7%

DIN 81%

River inputs of N to Horsens Fjord, Denmark

Inputs dominated by nitrate

DIN 17%PON 0%

DON 83%

Export from Horsens Fjord

Extensive transformations Export primarily as DONAvailability?Impact on food webs?Impact on coastal zone?

N2O and N cycling

NH4 NO2 NO3

N2

NO

N2O

Nitrification

DenitrificationOxic Anoxic

N2O is a greenhouse gas 100x more powerful than CO2

de Bie et al. 2002

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Peak N2O production in the Schelde estuary at low O2 concentrationsLow oxygen and some NH4

triggers N2O production in estuaries

Long-term monitoring records of dissolved silica (DSi) show declining concentrations in the Baltic with eutrophication and damming of riversDSi concentrations are generally not limiting today

Within the next 20-30 years DSi limitation will be common causing severe disruption of food webs in the Baltic Sea

Papush, Danielson and Rahm (Unpub. Data)

Long-term reductions in dissolved silicate in the Baltic Sea

Lancelot et al. 2002

Effects of N, P and Si concentrations and ratios

NAN

DIA

BAC

POM

DOM

Si

PO4

MZoo

µZoo

NO3

NH4

Sediment

OPP

NOCGEL

Recognition that differential loading of N, P and Si will effect the response of coastal ecosystems

Reductions in Si inputs disrupts diatom-based food web

Changes in N:P ratios will effect functional groups of algae

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Lancelot et al. 2002

Response of functional groups to nutrient forcing in the Danube River

1988-91

1994-95

diatomsnano flagellatesopportunistic species

copepodsmeso zooplanktonbacteria

MnemiopsisNoctiluca

Model used as a tool to assess changes in loads

Higher nutrient loads increased the diatom- copepod C transfer, but opportunistic species thrive later

Lowered nutrient levels enhanced the microbial food web

Combining model results with increased fishing pressure demonstrated that BOTH were important

De Wit et al. 2001

Regime shifts under eutrophication

Responses to eutrophication not always linear

Increase the load of nutrients until a sudden shift in ecosystem structure occurs

THRESHOLDSTHRESHOLDS

Coupled models of input and response needed

Summary

Data, data, data

From a recent EEA Assessment of marine eutrophication in Europe

Coupled models of input and response needed

Summary

Data, data, data

There is a need for long-term ecological research

Thank youvery many!