BENTHIC NUTRIENT REGENERATION IN THE ERSEM ECOSYSTEM MODEL OF THE NORTH-SEA

In any ecosystem modelling approach to shallow seas an adequate descri ption of the sediment-water interactions to all the essential nutrient s is necessary. With this aim a fairly simple concept has been develop ed and applied for the modelling of the nutrient cycles of N, P and Si which includes the essential diagenetic processes such as vertical tr ansport, oxic and anoxic mineralization, silicate dissolution, adsorpt ion, nitrification and denitrification. All these processes are explic itly formulated for one or more distinct layers in the sediment. The m odel contains a low number of variables and is efficient with respect to computer time. The model is part of the European Regional Seas Ecos ystem Model (ERSEM) of the North Sea, a joint effort of several instit utes around the North Sea. The benthic-pelagic coupling of the ERSEM m odel is discussed with emphasis on the consequences for the benthic nu trient cycling and the interrelations between the different benthic nu trient submodels. The results show that the model is able to describe the seasonal variation of nutrient fluxes including the sediment-water exchanges and the vertical profiles in the pore water. From the model results is concluded that changes in organic matter deposition direct ly influence the benthic nitrification and denitrification through cha nges in the oxygen availability to the nitrifiers and, due to this, th e supply of nitrate to the denitrifiers. Short fluctuations in organic deposition (e.g. after the spring bloom) are not reflected in the flu xes due to sorption buffering of phosphate in the oxidized surface lay er of the sediment.