In the framework of the project “AGRUM – Weser” a model instrument was developed to assess the regionally differentiated nitrogen
pollution of groundwater and surface waters and to predict the effects of nitrogen-reducing practices in agriculture. For this purpose
the agro-economic model RAUMIS was coupled with the hydrological models GROWA-DENUZ/WEKU and MONERIS. By combining
approaches to quantify the inputs from point sources and from diffuse sources with economic profitability analyses, the model instrument
was able to consider simultaneously the complex socio-economic and hydrological / hydrogeological interdependencies. The
focus was on integrative model analyses to evaluate the consequences of agricultural and ecopolitical nitrogen-reduction measures
aiming to reach quality targets in the context of the implementation of the EU Water Framework Directive. Initially the actual nitrogen
surpluses in agriculture (2003) and the nitrogen inputs into groundwater and surface waters were assessed. Based on this status-quo
analysis, the effects were predicted that will result from agricultural and environmental measures to be implemented by the year 2015
at EU level (baseline scenario) to reduce diffuse nitrogen surpluses on farmland and nitrogen inputs into groundwater and surface waters.
Then, the additional need for action to reach the good-quality status of groundwater and surface waters was identified. Finally, an
option and the resulting costs of combining nitrogen-reduction measures to achieve good groundwater quality are presented.