The results of a study on the riverine nutrient emissions and loads of nine river basins of the country Mecklenburg-Vorpommern to the Baltic Sea are presented for the period 1992 to 1994. The basins represent about 76% of the Baltic Sea catchment area of Mecklenburg-Vorpommern. The population living in the basins causes point emissions of 1752 tN/a and 293 tP/a. The analysis of diffuse emissions of nutrients is based on digitized maps of the land use and the soil types, the livestock numbers in the basins and measurements on the nutrient concentrations in the groundwater and drainage areas. The used method considers different pathways of diffuse sources as load from urban areas, erosion, load by groundwater, and drainage systems, atmospheric deposition, and direct load by agricultural activities. The dominant pathway of nitrogen emissions is the emissions of drainage. For phosphorus the emissions by erosion, groundwater and drainage are the main sources. The emissions of point sources contribute to the total emissions to 10% (N) and 25% (P), respectively. The measured nutrient load at the monitoring stations of the rivers is in all cases lower than the sum of the nutrient emissions. This behaviour can be explained by intensive retention processes in the rivers, which depends on the specific runoff, and for nitrogen additionally on the area of surface water in the basin.
Measures against the high nutrient load have to be focussed on the reduction of diffuse sources, especially the emissions of nitrogen and phosphorus by drainage systems have to be reduced, and additionally in the case of phosphorus the emissions by erosion and by direct agricultural load.
