Modelling subsurface nonpoint source nitrogen inputs to the Odra River

A study is being carried out for the Odra River basin to estimate and evaluate nutrient emissions into the river network via subsurface and surface routes. Modelling components integrated into a GIS allow for quantitative and spatially differentiated estimations of the nitrogen (N) load transported by seepage and groundwater. Lag time and nitrate decomposition are of decisive importance for the subsurface N transport. An adequate digital database was created and accordingly completed for the Polish and German parts of the Odra River basin (114 049 km(2)). Based on a still very elementary scenario, the subsurface N transport was evaluated for the period 1989-1990, the last year before the political change. The calculated load in the rivers amounted to more than twice the load measured at the Odra River mouth. This calculated load is expected to decrease further by taking into consideration more realistic assumptions of the nitrate transport and decomposition.