Gunter Wriedt

Identification and management of nitrogen retention in a shallow groundwater-stream system of a small lowland catchment (Northern Germany)

Diffuse nitrogen pollution in groundand surface waters is of concern, especially in regions with intense agricultural activities. Observed nitrogen (N) loads in surface waters often do not reflect the actual input. This apparent retention o f nitrogen can be explained by various chemical transformations and hydrological processes in soi!, groundwater and surface water. The quantification of these processes in the field is difficult, and models are needed to evaluate the interactions in space and time. The objective ofthis investigation was to quantify these processes and their interactions, since this is a prerequisite to develop measures to reduce nitrate loads in streams at the catchment scale. In this context it is important to know whether it is possible to use and manage the denitrification capacity in lowland catchments and if manipulation ofthis natural attenuation can be a useful strategy to deal with nitrate pollution (see also NAIMAN et al. 1989).