Hydrogeochemical studies of the influence of nitrate input and possible denitrification processes

The aquifer Halterner Sande in North Rhine-Westphalia (Germany) is intensively used for water supply. The area is also intensely agricultural with high nitrogen loads causing nitrate concentrations to very often exceed the critical value of 50 mg/l in the shallow groundwater which may cause transport of nitrogen into receiving waters. In this study, vertical transport of nitrate was monitored in three multi-level sampling devices to analyse the reactions in the groundwater. In addition, nine column experiments were performed to investigate the reduction potential of nitrate in sediments. The hydrochemical results presented here show decreased nitrate concentrations with greater depth in the multi-level sampling devices with possible redox reactions. These studies found variable nitrate reduction potentials, however they demonstrate the need to decrease nitrogen inputs into the aquifer.