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A model has been developed which estimates the magnitude and the spatial distribution of pesticide losses from diffuse sources (surface run-off, tile drains and spraydrift) into surface waters for the entire area of Germany. The cumulative annual losses of 42 active ingredients applied to 11 field crops, orchards and vineyards are calculated for river basins in Germany based on grid maps with a resolution of 1 x 1 km2. The model validation showed a sufficient degree of accuracy of the model results compared to measured pesticide loads in 13 small catchments. According to the model results the pesticide input from diffuse sources into surface waters amounted to 13.8 t in 1994 aggregated for the entire area of Germany. Input via surface runoff contributed 9.1 t while tile drainage was 1.4 t and spraydrift 3.4 t respectively. Alongside the model calculations empirical data of the pesticide load of rivers in Germany are presented. A comparison of the measured river loads with the modeled inputs from non-point sources leads to the conclusion that in most regions of Germany the largest portion of the load is due to the input from farm effluents.

A GIS-based model estimates the losses from diffuse sources in surface waters in Germany for 42 active ingredients applied to 11 field crops, vineyards and orchards. For the following pathways of entry: tile drainage, runoff and spray drift, the calculated mean pesticide input amounts to 1490 kg/year, 9060 kg/year and 3350 kg/year, respectively, in 1994. The model results are highly sensitive to the model parameters, primarily the chemical properties of the active ingredients. The modeled water inputs were compared with measured pesticide loads in smaller catchments and large river basins to validate model results. Both datasets agree as to the order of magnitude, nevertheless due to the scale of the study the results should be addressed mainly to comparative interpretations with the focus on the proportions between different active ingredients, soil regions, climates and application periods.