These waters benefit especially from nitrogen load reductions in German river catchments, which reduce phytoplankton

(indicated by chl.a) concentrations in coastal waters. The important role of the Odra river as major nutrient source in the western Baltic is very well visible. It controls water quality in the entire Pomeranian Bay, along the Polish coast and at coastal waters round the island of Rügen. About 95% of the Odra river basin is on Polish and Czech territory and beyond control of German selleck compound river basin management approaches. This underlines that a close cooperation of neighboring countries both within HELCOM and on WFD River Basin District level is extremely important. In the open western Baltic Sea our approach suggests factors of about 0.6 for TN and 0.5 for TP. The historic river loads were about 25% (TN) resp. 50% (TP) of the present nutrient loads, but caused TN and TP nutrient concentrations in the open sea of 60%, resp. 50% compared to today. The results clearly indicate that the outer German coastal waters (B3 and B4 types according to the WFD, see Fig. 6) and the open western Baltic Sea are not sensitive to load reductions in Germany and can hardly be controlled via German river basin management measures. Here, long-distance import of nutrients from other parts of the Baltic Sea and the Odra river largely determine water quality and are of high importance for the definition of water

quality thresholds. This is especially true for all eastern German

selleck inhibitor outer coastal waters. Input from the North Sea is of minor importance. Germany is largely not in control over the state of its outer coastal waters and the German Baltic Sea, but nutrient loads from German river basins determine the quality in inner coastal waters (B1 and B2 types according to the WFD, see Fig. 6). The factors were multiplied with recent monitoring data. Therefore, quality and reliability of water quality thresholds depend on quality of monitoring data. Fig. 7 and Fig. 8 give an impression of the strong interannual variability of data and of long-term trends. To receive reference concentrations for chl.a, Selleckchem Abiraterone for example, average annual summer data of every station were multiplied with the site specific factor (See Appendix A1 and A2). To receive stable and reliable reference concentrations for a station, the resulting (reference) data for every year were averaged. Fig. 5 shows site (monitoring station) specific chl.a reference concentrations, where a site specific factor was multiplied with different types of data (averages and medians over 6 resp. 11 years) of these sites. It gives an insight to what extent the interannual variability of monitoring data (which is shown in Fig. 3) is reflected in long-term medians and averages and how these differences effects our calculated reference and target thresholds. The difference between chl.