IWRA Proceedings

AbstractIntroduction The implementation schedule for the EU water framework directive requires the establishment of river basin district management programmes until 2009. In Germany, the reduction of nitrogen load into groundwater, mostly caused by diffuse emission from agriculture, is one of the most challenging tasks. 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. Objective The definition of environmental objectives is an indispensable precondition for assessing the required amount and efficiency of water protection measures. In the WAgriCo-project a nitrate concentration in percolation water of 50 mg/l has been defined as the environmental target for groundwater protection. This value, however, is regarded as an average for a larger area defined by the groundwater bodies and their hydrogeological subdivisions rather than as for each individual site. For each of these subdivisions, the current pressure of agriculture to groundwater is quantified. For the evaluation of the amount and efficiency of certain water protection measures, the required reduction of N-surpluses to accomplish the environmental target needs to be quantified, using the current status as a reference. Methods A integrative macroscale agroeconomic-hydrogeological 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 on a 50 x 50 m resolution considering site-characteristics, N-surpluses, 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 “inverse” 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. Conclusion Within the WAgriCo project a number of measures and measure combinations with detailed management prescriptions were selected and evaluated with regard to its potential N-surplus. By using the nitrogen export model their effects are assessed with respect to the nitrate leaching to groundwater and surface waters. The measures effectivenesses and its needs are evaluated area-differentiated for each of the areas considered.