Management options to reduce future nitrogen emissions into rivers: A case study of the Weser river basin, Germany

The European Water Framework Directive (WFD) requires a good chemical and ecological status of water and groundwater resources in the EU member countries by 2015. However, for some river basins, the good status cannot be achieved by 2015, and therefore measures have to be taken to reduce the unacceptably high nutrient input. Therefore, a new approach was developed by using an interdisciplinary model network, consisting of the regionalized agricultural economic model RAUMIS and two hydro(geo)logical models GROWA/WEKU and MONERIS. For the 49,000 km2 Weser river basin, in Germany we: (1) analysed nitrogen surplus on agricultural land for 2003 and nitrogen emissions into ground and surface waters in an area-differentiated manner, (2) quantified the future impact of agro-political measures and global economics for 2015 and its effect on nitrogen emissions (baseline scenario), (3) identified reduction targets to reach the goals of the WFD and (4) designed comprehensive measure packages including cost efficiency. In 2003, high nitrogen balances lead to nitrogen emissions of 91,000 t yr−1, which were mainly realized via the pathways groundwater flow, tile drainages and point sources. In 2015 the baseline scenario shows a mean reduction of nitrogen balances of ∼10 kg ha−1 yr−1. Consequently, nitrogen emissions into surface waters are predicted to drop to 75,700 kg ha−1 yr−1 for the whole catchment, and sitespecific emissions will remain under 30 kg ha−1 yr−1. However, despite this reduction, additional measures will be needed in order for agriculture to reach the targets for the good ground and surface water quality. Therefore, seven conventional agricultural measures were chosen based on a comprehensive literature research and expert opinions. Results show, that in 6% of the regions the targets are not attained by conventional measures. This interdisciplinary model network provides an appropriate tool for a sustainable river basin management for large scales.