Nitrogen monitoring in groundwater in the sandy regions of the Netherlands

The Nitrate Directive of the European Communities sets goals for preventing pollution and reducing existing nitrate concentrations in groundwater. Establishment of an action program is one of the obligations Member States have, to ensure the reduction of nitrate leaching and runoff. The effectiveness of the action program by Member States must be determined by regular monitoring of such items as groundwater quality. The study documented here regarding the Dutch effort within this action program, was aimed at quantifying both the nitrate concentration in shallow groundwater of the sandy regions of the Netherlands and the land area where the EC limit value is exceeded. Since shallow groundwater quality is influenced by variation in precipitation, nitrate concentrations were adjusted to be representative for average precipitation. Using monitoring results and geographical information, we calculated that the EC limit value (LV) of 50 mg l−1 for nitrate in groundwater was exceeded in 77–85% of the land area in the Netherlandsʹ sandy regions. The LV was found to be exceeded in a calculated agricultural area of 890,000–940,000 ha (94–99% of total agricultural area), and a forest and heath area of 60,000–86,000 ha (21–30% of total forest and heath areas).