Report: "Nutrients in the German coastal waters of the Baltic Sea and adjacent areas"

¿Phosphorus inputs from the eight largest sewage treatment plants on the German Baltic Sea coast (about 70 % of direct Dischargers) decreased by 98 % between 1990 and 2008. In the same period, nitrogen input decreased by 89 % (about 90 % of direct Dischargers). A comparison of the periods 1986/90 and 2004/08 shows that riverine discharges of total phosphorus decreased by 61 %, primarily due to reduced inputs from point sources. Nitrogen input, mostly from diffuse sources, decreased only by 13 %, half of the decrease being assigned to lower runoff. The distribution pattern of phosphate concentrations in winter shows that levels in the inner coastal waters are in the same order of magnitude as in the open sea. By contrast, nitrate concentrations are 50 times higher than in the open sea due to the fact that diffuse sources prevail in the drainage area and that nitrate levels are closely coupled to runoff in the inner coastal waters, especially in the Estuaries of the river Odra including Haff and Peenestrom, the rivers Warnow and Trave. Thesis reduced inputs are also reflected in the decline of total phosphorus and nitrogen concentrations, both in the inner coastal waters and in the adjacent Baltic Sea waters. The strongest decline was recorded up to the mid-1990s, after which concentrations have fluctuated at a relatively stable level, often associated with runoff. Nevertheless, all areas still have to be considered eutrophied, in accordance with the HELCOM classification (HELCOM [2009]). Water quality in the open sea areas (western Belt Sea, Kiel Bight, Arkona Basin, Zingst outer coast) is classified as moderate, whereas waters closer to the coast and in more enclosed areas (Flensburg Fjord, southern Kiel Bight, Lübeck Bight, Wismar Bight, and Pomeranian Bight) have to be classified as ‘bad’applying the WFD assessment criteria. Eutrophication is particularly high in the inner coastal waters (Schlei, Lower Trave, Lower Warnow, Darss-Zingst Bodden Chain, Jasmund Bodden, Peenestrom, Kleines Haff). The orientation values for inner coastal waters are exceeded several times and apparently have been set too low, especially because of their missing gradients towards the open Baltic Sea. They require scientific review. Phosphorus input from the eight most important sewage treatment plants on the German Baltic Sea coast (approximately 70 % of direct instructors) decreased by 98 % between 1990 and 2008. Nitrogen input decreased by 89 % during the same period (approximately 90 % of direct inductors). The flow rate of total phosphorus decreased by 61 %, compared to 1986/90 and 2004/08, mainly due to reduced cargo from point sources. The nitrogen input mainly from diffuse sources has decreased by only 13 %, of which half of the decrease is due to the lower discharge. The distribution patterns of winter phosphate concentrations show that the values in the internal coastal waters are of the same order of magnitude as in the open sea. On the other hand, the dominance of diffuse springs in the catchment area and the close coupling to the outflow in the internal coastal waters, especially in the estuaries of the Oder with Haff and Peenestrom, the Warnow and the Trave, causes nitrate concentrations, some of which are 50 to 70 times higher than the values of the open seas. The reduced inputs are also reflected in the decrease in total phosphorus and nitrogen concentrations, both in the internal coastal waters and in the upstream Baltic Sea. The strongest decline took place until the mid-1990s, after which the values fluctuated at a relatively stable level, often coupled to the outflow. Nevertheless, all areas must still be assessed as eutrophicated, in line with the HELCOM assessments (HELCOM [2009]). The open sea areas (Western Beltsee, Kiel Bay, Arkona Basins, Zingster Outer Coast) have a moderate water status. On the other hand, the coastal and more closed regions (Flensburg Fjord, southern Kiel Bay, Lübeck Bay, Wismar Bay and Pomerania Bay) must be assessed as poor in accordance with the WFD assessment criteria. The inner coastal waters have a particularly high degree of eutrophication (Schlei, Untertrave, Unterwarnow, Darß-Zingster Boddenkette, Jasmunder Bodden, Peenestrom, Kleines Haff). The orientation values for internal coastal waters are exceeded many times over and appear to be underestimated, also and especially because of their lack of gradients to the open Baltic Sea, and require a scientific review.