Coupling of hydrological and agro-economical models to assess the impacts of nitrogen reduction measures on the nitrogen load in rivers

The REGFLUD-project, commissioned by Germany’s Federal Research Ministry (BMBF), addresses the problem of reducing diffuse pollution from agricultural production. The objective of the project is the development and application of multicriteria scientific methods, which are able to predict diffuse pollution in river basins subject to economic feasibility and social acceptability. The selected river basins (the entire Ems basin and sub-catchments of the Rhine) cover a variety of landscape units with different hydrological, hydrogeological and socio-economic characteristics. This paper focuses on the analysis of the effects of certain policy measures to reduce diffuse pollution by nitrogen. For this purpose a model system consisting of an agricultural sector model, a water balance model and a residence time/denitrification model was combined and applied. First results indicate a wide range of annual nitrogen surpluses for the rural areas between less than 10 N ha·a up to 200 kg N ha·a or more, depending on the type and intensity of farming. Compared to the level of nitrogen surpluses the level of nitrogen inputs into the surface waters is relatively moderate because of degradation processes during transport in soil and groundwater. Policy impact analyses for a nitrogen tax and a limitation of the livestock density stress the importance of regionally adjusted measures.