Eutrophication of the southern North Sea:problematic, studies and outlook

based on the presentation of Lacroix et al. (2009):Does reducing river nutrient loads impact on eutrophication and

transboundary nutrient fluxes in Belgian waters? A modeling study

Sollberger (2009)

Chemical Oceanographic UnitUniversity of Liege

Introduction Modeling Results Conclusion & outlook References

Contents

1 Introduction

2 Modeling

3 ResultsReduction of nutrient loadsTransboundary flux

4 Conclusion & outlook

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Introduction Modeling Results Conclusion & outlook References

Background

Left panel: Density map ofthe inhabitants of westernEurope. Schematic viewof the general circulationthrough the South Bight ofthe North Sea (black ar-rows). Simplified represen-tation of the inputs of theRhine, Meuse and Scheldtriver (blue arrows).Right panel: Chlorophylla concentration (mg Chl

m−3) viewed by satelliteimage averaged on April2008.

Characteristics of the region

I Heavily industrialized zone

I Phaeocystis blooms dominance

I Shallow waters

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Introduction Modeling Results Conclusion & outlook References

The MIRO model (Lancelot et al., 2005)

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Introduction Modeling Results Conclusion & outlook References

Reduction of nutrient loads (Lacroix et al., 2009)

Concentration criteria to be considered aspositive for degree of enrichment (DIN, DIP,N:P) and for direct consequences of enrich-ment (Chl a, Phaeo.)

BCW BOWDIN > 15 > 12DIP > 0.8 > 0.8N:P > 24 > 24Chl a max. > 15 > 8Chl a mean > 7.5 > 4.2Phaeocystis > 150 > 150

Results

I High concentrations of DIN, DIP,Phaeo. in BCW

I Low concentrations of DIN, DIP,N:P, Chl a in BOW

I Higher concentrations northern

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Introduction Modeling Results Conclusion & outlook References

Transboundary flux (Lacroix et al., 2009)

Importance of fluxes

I France → Belgium

I Belgium → TheNetherlands

I Belgium → UnitedKingdom

Net transport:F→Be + UK→Be − Be→NL

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Introduction Modeling Results Conclusion & outlook References

Conclusion & outlook

Criteria of eutrophication (Lacroix et al., 2009)

Def. Cat. I Cat. IIProblem Area (PA) + +Potential Problem Area (PPA) + −Problem Area (PA) − +Non Problem Area (NPA) − −

Conclusion

I Higher reduction than

expected (> 50 %)

70 %90 %

I Work on agriculturalfertilizer to reduce DIN load

I Intensity AND duration ofthe Phaeocystis blooms

I Investigation of the N:Pratio through the organisms

I Huge cost

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Introduction Modeling Results Conclusion & outlook References

References I

Ærtebjerg, G., Carstensen, J., Dahl, K., Hansen, J., Nygaard, K., Rygg, B.,Sørensen, K., Severinsen, G., Casartelli, S., Schrimpf, W., Schiller, C.,Druon, J.-N., and Kunitzer, A. (2001). Eutrophication in Europe’s coastalwaters. Topic Report, European Environment Agency, 7:3.

Dippner, J. W. (1998). Competition between different groups of phytoplanktonfor nutrients in the southern North Sea. J. of Mar. Sys., 14:181–198.

Ducrotoy, J.-P., Elliott, M., and De Jonge, V. N. (2000). The North Sea.Marine Pollution Bulletin, 41(1-6):5–23.

Lacroix, G., Ruddick, K., Gypens, N., and Lancelot, C. (2009). Does reducingnutrient loads impact on eutrophication and transboundary nutrient fluxes inBelgian waters? A modeling study. 41st International Liege Colloquium onOcean Dynamics, 4-8 May.

Lancelot, C., Spitz, Y., Gypens, N., Ruddick, K., Becquevort, S., Rousseau, V.,Lacroix, G., and Billen, G. (2005). Modelling diatom and Phaeocystisblooms and nutrient cycles in the Southern Bight of the North Sea: theMIRO model. Mar. Ecol. Prog. Ser., 289:63–78.

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Introduction Modeling Results Conclusion & outlook References

References II

Peperzak, L., Colijn, F., Gieskes, W. W. C., and Peeters, J. C. H. (1998).Development of the diatom-Phaeocystis spring bloom in the Dutch coastalzone of the North Sea: the silicon depletion versus the daily irradiancethreshold hypothesis. J. of Plank. Res., 20:517–537.

Rousseau, V., Becquevort, S., Parent, J., Gasparini, S., Daro, M. H., Tackx,M., and Lancelot, C. (2000). Trophic efficiency of the planktonic food webin a coastal ecosystem dominated by Phaeocystis colonies. J. Sea Res.,43:357–372.

Thieu, V., Polard, A., Gypens, N., Billen, G., Garnier, J., Hecq, W., Rousseau,V., and Lancelot, C. (2009). Impact assessment of nutrient reductionpolicies on coastal Phaeocystis blooms: an integrated modeling approach.41st International Liege Colloquium on Ocean Dynamics, 4-8 May.

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