Excessive manuring and its effects on the nitrogen and phosphorus concentrations in soil, ground- and surface water of the North-West Veluwe (The Netherlands)

The present study describes an extension of the PAWN-experience, assessing the impacts of excessive manuring with respect to phosphorus and nitrogen loads on surface and ground water. For a first application of the methodology the North-West Veluwe was chosen vecause of: a) the excessive manuring in this region; and b) the serious eutrophication problems in the border lakes at the north-west side of the district, where all of the districts surplus water drains. In order to quantify the fluxes of N and P to surface and ground water two models were developed that describe physical, chemical and biological processes in the unsaturated zone (top one meter of the soil). The Nitrogen Soil Load model (NITSOL) describes the concentration of several N-components (NH4+, NO3-, org.N, refr.N) and the fluxes of these components to ground and surface water. The Phosphorus Soil Load model (PHOSOL) describes the saturation of the soil adsorption complex with phosphorus. Both models are calibrated on existing geochemical data and the results of field experiments and surveys in the district and equivalent areas with sandy soils.