EUTROPHICATION MODELING OF THE NORTH-SEA - 2 DIFFERENT APPROACHES

Two different eutrophication models as applied to the North Sea are di scussed in this paper. The ERSEM (European Regional Seas Ecosystem Mod el) model, being developed in the framework of the EU Marine Science a nd Technology program, is a complex (70 state variables) ecosystem mod el which dynamically simulates the large-scale cycling of carbon, oxyg en and the macronutrients N, P and Si over the seasonal cycle. The mod el consists of an interlinked set of modules, describing the biologica l and chemical processes in the (stratified or non-stratified) water c olumn and in the (vertically layered) benthic system, as forced by lig ht and temperature. Advective and diffusive transport is included by d riving the model with the output of the 3D General Circulation Model o f the North Sea by Backhaus, aggregated into daily exchange volumes be tween the ICES (International Council for the Exploration of the Sea) boxes, which form the spatial compartments of the model. The other mod el, MIKE21 EU, consists of an advanced 2D circulation model in combina tion with modules describing advection-dispersion processes, oxygen dy namics and carbon/nutrient cycling in the lower trophic levels. The ca rbon and nutrient dynamics (N and P) are aggregated into 12 state vari ables. The horizontal spatial resolution of the model is very high, wi th a cell size of 18.5 x 18.5 km. Both models include the freshwater i nflows and the associated organic and inorganic nutrient loadings as w ell as cross-boundary flows as time series of flow rates and concentra tions. The suitability of either model to address eutrophication-relat ed questions is exemplified.