Model system for the management of nitrogen leaching at the scale of riverbasins and regions

In the framework of the EU-project RANR (Regional analysis of subsurface ni trogen retention and its impact on the nitrogen export from land to sea) a model system was developed to estimate groundwater-borne nitrogen inputs in to river systems. The core of this model system is composed of a soil nitro gen leaching model (SOIL-N) and a groundwater residence time/denitrificatio n model (WEKU). The application of the model system was carried out for the study catchment areas of the Uecker basin (ca. 2400 km(2), Germany) and th e Gjern basin (ca. 200 km(2), Denmark). For both catchment areas, the model led average nitrogen loads leached into the groundwater were about 40 kg N/ ha a, while the remaining groundwater-borne nitrogen intake to rivers was q uantified to an average of about 2 kg/ha a. The comparision with observed g roundwater-borne riverine nitrogen loads showed a very good agreement, proo fing the key role nitrogen retention in groundwater plays in the two catchm ent areas. With regard to the generalisation and transfer of the SOIL-N/WEK U model concept we assume that the model can be applicated in catchment are as in the European Pleistocene Lowland, which ranges from the Netherlands i n the west to the Baltic States and the Ukraine in the east.