Conceptual hydro(geo)logical model for assessments of measures to reduce groundwater contamination by nitrate

In Germany, about 1,000 groundwater bodies were delineated, of which almost 40% do not reach the quality target set by the EC Water Framework Directive (WFD) for the good chemical status", primarily because of their high nitrate concentrations. Accordingly, programmes of measures were initiated to reduce the nitrate pollution of groundwater by minimising the excessive application of nitrogen in agricultural practices. A three-tier conceptual hydro(geo)logical model was developed to evaluate the efficiency of such measures on the basis of data available in the German Federal States. The first tier consists of analyses of interrelations between land use, nitrate concentrations measured in groundwater and in the hydrogeological system; moreover, potential hotspots are identified. The second tier is an assessment of the reduction of N excesses in agriculture that is necessary to reach the quality target for groundwater of 50 mg/l NO3. The third tier evaluates the time elapsed between the introduction of a nitrogen-reducing measure and its impact on the nitrate concentrations at the groundwater-monitoring stations. The methodology was successfully tested in a groundwater body situated in the North German Lowland that is displaying typical nitrate-pollution patterns.