Advances in Geosciences www.adv-geosci.net 1680-7340 1680-7359 5 Proceedings of the 8th Workshop for Large Scale Hydrological Modelling - Oppurg 2004 2005 10.5194/adgeo-5-7-2005 http://www.adv-geosci.net/5/7/2005/ http://www.adv-geosci.net/5/7/2005/adgeo-5-7-2005.html http://www.adv-geosci.net/5/7/2005/adgeo-5-7-2005.pdf 7 12 2005-12-16 Modelling of point and non-point source pollution of nitrate with SWAT in the river Dill, Germany T. Pohlert J. A. Huisman L. Breuer H.-G. Frede Institute for Landscape Ecology and Resources Management, University of Giessen, Heinrich-Buff-Ring 26, 35392 Giessen, Germany We used the Soil and Water Assessment Tool (SWAT) to simulate point and non-point source pollution of nitrate in a mesoscale mountainous catchment. The results show that the model efficiency for daily discharge is 0.81 for the calibration period (November 1990 to December 1993) and 0.56 for the validation period (April 2000 to January 2003). The model efficiency for monthly nitrate load is 0.66 and 0.77 for the calibration period (April 2000 to March 2002) and validation period (April 2002 to January 2003), respectively. However, the model efficiency for daily loads is low (0.15), which cannot only be attributed to the quality of input data of point source effluents. An analysis of the internal fluxes and cycles of nitrogen pointed out considerable weaknesses in the models conceptualisation of the nitrogen modules which will be improved in future research.