|Modelling the response of coastal ecosystem to nutrient change|
Lancelot, C.; Staneva, J.; Gypens, N. (2004). Modelling the response of coastal ecosystem to nutrient change. Océanis (Paris) 28(3-4): 531-556
In: Océanis (Paris). Institut Océanographique: Paris. ISSN 0182-0745
coastal eutrophication; planktonic food-web; biogeochemical modelling
|Auteurs|| || Top |
- Lancelot, C.
- Staneva, J.
- Gypens, N.
The response of coastal seas to changes in riverine nutrient loads has been investigated with a complex generic biogeochemical model describing C, N, P and Si cycling through aggregated chemical and biological components of the pelagic and berithic realm. The trophic resolution of the model was based on current understanding of biological processes governing phytoplankton community shifts in response to nutrient changes, food chain bifurcations and nutrient remineralisation processes. Model runs were applied in the north-western Black Sea and eastern Southern Bight of the North Sea where last decade changes in riverine nutrient loads suggest some transition from Si towards a nowadays P limitation of algal blooms. Model results reveal some important features of coastal eutrophication process and point out the key role played by phosphate in driving nowadays diatom productivity and ecosystem structure and function of these river nutrient-influenced coastal systems. According to our model runs, diatoms are blooming early in the season and assimilate N, P and Si follows their stoichiometry. Low N and/or P with respect to dissolved silicates (DSi) availability prevent diatoms of blooming challenging the currently admitted concept of diatoms being better competitors for inorganic nitrogen and phosphate when dissolved silicate is still sufficient. On the other hand diatom leftover excess N and/or P stimulates blooms of large non-siliceous phytoplankton which escape zooplankton grazing but benefit to the microbial network. Trophic dead-end gelatinous zooplankton (both omnivores and carnivores) also benefit from the nutrient-stimulated biomass production but impact negatively on the diatom -> copepod -> fish linear food chain. From these model runs we conclude that coastal eutrophication problems can no longer be seen as resulting of the over-enrichment of solely N and/or P but Si fluctuations and the N:P:Si signature of nutrient loads must be considered as well.