The ecosystem model ERGOM-MOM is an integrated biogeochemical

model linked to a 3D circulation model covering the entire Baltic Sea. A horizontal resolution of 1 nautical mile (nm) is applied in the western Baltic Sea and in inner and outer coastal waters. The vertical water column is sub-divided into layers with a thickness of 2 m. The biogeochemical model consists of nine state variables. This model is coupled with the circulation model via advection diffusion equations for the state variables. The nutrient variables are dissolved ammonium, nitrate and phosphate. Primary production is represented by three functional phytoplankton groups: large cells, CB-839 order small cells and nitrogen fixers. A dynamically developing bulk zooplankton variable provides grazing pressure on

the phytoplankton. Accumulated dead particles are represented in a detritus state variable. During the process of sedimentation a portion of the detritus is mineralized into dissolved ammonium and phosphate. Another portion reaches the sea bottom where it accumulates as sedimentary detritus and is subsequently buried, mineralized or resuspended in the water column. Under oxic conditions parts of phosphate are bound to iron oxides in the sediment, but can be mobilized under anoxic conditions. Oxygen concentrations are calculated from biogeochemical processes via stoichiometric ratios and control processes such as denitrification and nitrification. Neumann Methocarbamol [35], Neumann et al. [36] and Neumann and Schernewski JAK/stat pathway [37] provide detailed model descriptions and validations.

Recent comparative studies [19], [30] and [20] proved that the biogeochemical model ERGOM is sufficiently reliable in the western Baltic Sea and suitable for scenario simulations. Weather data for the present time were taken from the Rossby Center Atmosphere model RCA3.0 on the basis of ERA-40 [28]. For the historical simulations the weather reconstruction of Schenk and Zorita [43] was used. Riverine nutrient input for 1970–2000 was provided by the Baltic Nest Institute (BNI) including 80 catchment areas around the Baltic Sea. After 2000 the official HELCOM Pollution Load Compilation (PLC-5) data [23] for riverine nutrient input was used. Since PLC provides only aggregated country-wise data for the nine Baltic Sea basins, the country loads were allocated according to the share of each river in BNI data. The historic nutrient loads of 16 main Baltic rivers, outside Germany, were reconstructed by following the approach of Gustafsson et al. [21] and all loads attributed to these rivers. The atmospheric nutrient input was computed by distributing the loads taken from Ruoho-Airola et al. [40] for every sub-region including a decline towards the open sea.