Abstract

Three organisations investigate the potential nitrate load to groundwater due to agricultural activities in the South-Limburg region of the Netherlands. These organisations have recorded discrepancies between networks in measure nitrate concentrations in soil moisture in the unsaturated zone, which is leaching to groundwater. These discrepancies could be attributed to differences in soil moisture extraction methods. RIVM has carried out a review of the scientific, peer review literature about methods that are used to measure nitrate concentrations in and/or leaching from the unsaturated zone. This review showed that there is no preferred method. It is uncertain whether additional laboratory or field research will provide clarification. The institutions involved are the Water Supply Company Limburg (WML), the Province of Limburg and the RIVM. WML carries out research within the groundwater protection zones in the South-Limburg region, the research of the Province of Limburg is performed on the main loess plateaus, and RIVM does research in the entire region. The study is performed on request of a task force that looks into the causes of the found discrepancies in nitrate concentrations. WML discovered to measure lower nitrate concentrations than the RIVM. A survey made by WML and RIVM showed that all protocols are sound and well underpinned. Because the measured nitrate concentrations are close to the target value (50 milligram per litre), the differences are relevant from a policy point of view.