Large-scale modelling of P-inputs from point and diffuse sources in German river basins

Mean annual P-inputs from diffuse and point sources in large river basins can be quantified with the MEPhos model. Its emission approach is described, which distinguishes between both eight different input pathways (municipal waste water treatment plants, industrial plants, combined sewer overflows, rainwater sewers, artificial drainage, erosion, wash-off, groundwater-borne runoff) and various types of critical source areas named phosphotopes.Then, the results of a model application to two large-scale river basins are presented and discussed. The river basins (ca. 12,500 km²) each show contrasting natural conditions, land use patterns as well as population and industry densities. Total P-emissions from each river basin range around 1,600 tonnes per year but the importance of sources varies significantly. While in the Ems river basin 87 % of all P-inputs originate from diffuse sources, their portion achieves only 32 % in the Rhine river sub-basin. Due to the fact that diffuse entries are mainly made up by erosion (11 % of all P-inputs), measures for tackling P-inputs will aim at erosion prevention and sediment retention.