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Schernewski, G., Neumann, T., Wielgat, M.: Referenzwerte für Hydrochemie und Chlorophyll-a in deutschen Küstengewässern der Ostsee. (Hydro-chemical and chlorophyll-a reference conditions in southern German Baltic coastal waters according to the European Water Framework Directive) Rostock. Meeresbiolog. Beitr., 15: 7-23, 2006.


We applied two models for the simulation of historic trophic conditions in German Baltic coastal waters: a 3-D circulation model with a biogeochemical module (ERGOM) for the complete Baltic Sea as well as a simple box-model for a lagoon. The aim is to provide reference data for nitrogen, phosphorus and chlorophyll, which is required for the implementation of the European Water Framework Directive (WFD). We assume that the trophic situation a century ago is well suitable as a reference. We focused on German outer coastal waters as well as the Szczecin (Oder) Lagoon. The Baltic Sea and the lagoon are controlled by nutrient loads from river runoff. Based on literature, we calculated historical loads for the early industrial state about 100 years ago which were used as input data for the model.

For the mixed surface layer of the coastal German Baltic Sea, we calculated maximum winter concentrations for dissolved phosphorus (dissolved inorganic nitrogen) of 0.3 (3) mmol m-³ for the situation a century ago. Maximum chlorophyll-a concentrations are around 2.5 mg m-³. A total phosphorus reference concentration of 0.35 mmol m-³ for the German outer coastal waters seems to be realistic and is in agreement with reference concentrations of 0.6 mmol m-³ TP suggested for near shore Baltic coastal waters. The concentrations of all parameters vary for different coastal waters, depending on exposure to nutrient sources, and show strong interannual variability.

For the Szczecin (Oder) Lagoon, the box model shows for the historic state only 35 % (15 %) of the recent total nitrogen (total phosphorus) concentrations. We sug-gest reference concentrations for the Kleines Haff (small lagoon) of 30 mmol m-³ TN and 0.8 mmol m-³ TP. For the Wielki Zalew (large lagoon) we suggest 42 mmol m-³ TN and 0.9 mmol m-³ TP. A century ago, chlorophyll concentrations were about 70 % lower throughout the vegetation season and reference values of 17 (24) mg m-³ Chlorophyll-a for the Kleines Haff (Wielki Zalew) are calculated. Different than today, primary production was not limited by light 100 years ago but nutrients played an important limiting role. All model applications are based on simplifications and therefore certain weaknesses and limitations are innate, which are briefly discussed.

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