Integrated modelling of water and nitrate fluxes in large catchment areas – assessing the needs and efficiencies of agroenvironmental measures for selected groundwater bodies in Germany.

Within the EU-Life project WAgriCo (Water Resources Management in Cooperation with Agriculture) nitrogen management options adapted to hydrological and agro-economic site properties are developed and implemented for three pilot areas in the Federal State of Lower Saxony using new participation approaches and technologies suitable for programmes of measures to reduce diffuse pollution from agriculture. As a target value for water protection measures a nitrate concentration in percolation water of 50 mg/l as an average for groundwater bodies and their hydrogeological subdivisions has been defined. An integrative emission model is used to simulate the interactions between agricultural practice, nitrogen surpluses and the nitrogen flow through the soil and aquifer to the outflow into surface waters. The actual nitrate concentrations in percolation water are calculated for the entire Federal State of Lower Saxony considering site-characteristics, Nsurpluses, water balance and denitrification in the soil. The tolerable N-surpluses needed to meet the environmental target are quantified as averages for each of the hydrogeological subdivisions by “backward” calculation using this model system. The required reduction of N-surpluses can then be estimated by comparing the tolerable N-surpluses to the actual state of nitrogen emission. For the evaluation of the amount and efficiency of water protection measures, the required reduction of N-surpluses to accomplish the environmental target is quantified, using the current status as a reference.