ASSESSING THE DIFFUSE PHOSPHORUS INPUT FROM SUBSURFACE TO SURFACE WATERS IN THE CATCHMENT-AREA OF THE LOWER RIVER SPREE (GERMANY)

The proportion of nonpoint phosphorus sources in the eutrophication process of surface waters is higher than generally assumed. In the surroundings of Berlin (glaciofluvial deposits and moraine areas) the phosphorus content of some subsurface waters reaches levels of several hundred mugP/l. As surface waters are mainly fed by groundwater in this area, nutrient contents in groundwater may become of great importance when other phosphorus sources are eliminated. Investigations in unpolluted areas are a prerequisite to decide whether higher phosphorus levels in groundwater are of natural origin or the result of contamination processes. The phosphorus background was shown to be very different and dependent on the depth below groundwater surface, content of iron, and redox conditions in the aquifer. Wastewater land treatment, bank filtration, agricultural land use, and degradation of lowland bogs were found to be sources of phosphorus contamination of aquifers. The results of observations are reported.