Scenarios for the reduction of nitrogen inputs to achieve the groundwater and marine protection goals in Mecklenburg-Vorpommern

The GROWA-DENUZ-WEKU model system has been used to simulate nitrogen (N) inputs into groundwater, surface waters and the coastal waters in Mecklenburg-Vorpommern. Area-wide model analyses have been performed in high spatial resolution (100 mx 100 m) for six diffuse and four point-source input pathways. Within the framework of a status quo analysis,hotspot-areas of N pollution and priority areas for the implementation of N reduction measures according to the requirements of the EU Water Framework Directive (EU-WFD) have been identified. It becomes apparent that presently 95 % of all N-inputs into surface waters originate from diffuse sources with N inputs from drainage systems as the dominating input pathway. The sum of all N-inputs from point sources accounts for just 5 % of all N-inputs (ca. 1,470 t N/a). The displaceable N inputs into soil would have to be reduced by ca. 41,500 t N/a in order to comply with the EU target value for groundwater (50 mg NO3/l) on the long run. Scenario analyses to forecast the impact of measures to reduce the agricultural N-balance show that further efforts are necessary to reach the target value for groundwater. Even the introduction of an area-covering limit of 50 kg N/(ha.a) for the agricultural N-balance would entail a further reduction by ca. 21,000 t N/a in order to reach the EU target value for groundwater. However, the target values for the North Sea (2.8 mg N/l) and the Baltic Sea (2.6 mg N/l) would already almost be reached when reducing the agricultural N-balance in this magnitude. Therefore, the area wide implementation of N reduction measures for groundwater protection should also have a high priority in the implementation of measures to reach the target values for the marginal sea.