Point and diffuse load of nutrients to the Baltic Sea by river basins of north east Germany (Mecklenburg-Vorpommern)

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 p resented for the period 1992 to 1994. The basins represent about 76% of the Baltic Sea catchment area of Mecklenburg-Vorpommem. The population living in the basins causes point emissions of 1752 tN/a and 293 tP/a. The analysi s 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 measurement s on the nutrient concentrations in the groundwater and drainage areas. The used method considers different pathways of diffuse sources as load from u rban areas, erosion, load by groundwater, and drainage systems, atmospheric deposition, and direct load by agricultural activities. The dominant pathw ay of nitrogen emissions is the emissions of drainage. For phosphorus the e missions by erosion, groundwater and drainage are the main sources. The emi ssions 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 ri vers, which depends an the specific runoff, and for nitrogen additionally o n the area of surface water in the basin. Measures against the high nutrient load have to be focussed on the reductio n of diffuse sources, especially the emissions of nitrogen and phosphorus b y drainage systems have to be reduced, and additionally in the case of phos phorus the emissions by erosion and by direct agricultural load. (C) 1998 P ublished by Elsevier Science Ltd. All rights reserved.