Use of early warning monitoring systems for groundwater protection in a policy decision context
Institute for Public Health and the Environment (RIVM)
A recent comparison of monitoring networks showed that sampling methodology strongly affects the measured nitrate concentrations in soil moisture in the vadose zone, affecting the evaluation of Dutch manure policies. The European Nitrates Directive aims at the reduction of nitrate pollution by agriculture. It obliges Member States to abate and prevent groundwater and surface water pollution and to monitor the effectiveness of the actions carried out to comply with the Directive. To ensure that these obligations are met, different early warning monitoring systems have been developed during the last decade. To ensure equal compliance among Dutch soils with large differences in hydro geochemical properties all these systems focus on the assessment of nitrates in soil moisture leaching the rooting zone.The Loess region, in the southern part of the Netherlands, is the smallest of the four soil type regions. Groundwater levels are often deep (>>5 m below surface level) and, therefore, soil moisture is extracted from the soil layer below the root zone to monitor nitrate leaching. Within this region, the national authority (RIVM), the Province of Limburg and the Water Supply Company Limburg (WML) have their own early warning monitoring network. RIVM carries out on-farm monitoring within the entire Loess region as part of the national Minerals Policy Monitoring Programme (LMM). The Province of Limburg carries out a comparable monitoring programme called the ‘Soil Moisture Monitoring’ (BVM). BVM focuses at agricultural fields on the so-called plateaus. These plateaus (higher areas) cover about two-third of the LMM Loess region. The Water Supply Company Limburg is responsible for the project ‘Sustainable Clean Groundwater’ (DSG). DSG aims to ensure the protection of groundwater resources. This project is carried out in co-operation with farmers within the groundwater protection zones.At the beginning of 2014 questions were raised in the agrarian press and the Dutch Parliament about the LMM monitoring protocol for the Loess region. An exploratory research of WML had shown that the WML protocol resulted in 30-40% lower measured nitrate concentrations. As nitrate concentrations in soil moisture are currently not much above the standard of 50 mg/l in the Loess region, this difference between protocols may lead to opposite conclusions. In case of the WML protocol, the conclusion is that almost no additional measures are required, while in case of the LMM protocol, one concludes that still additional measures are needed. WML, the Province of Limburg and RIVM are currently carrying out research – together with other relevant organisations – to determine the extent and cause of this difference. From 2014 onwards, farmers in the Loess region are confronted with additional measures that limit both the use of animal manure and of artificial nitrogen fertiliser to a greater extent than in some other regions. Therefore, the outcome of this research is relevant for farmers in this region. This paper will discuss the scientific, managerial and political dimensions of this research.