Nitrate in the uppermost groundwater under agricultural holdings in the Netherlands, 1992-2002
The nitrate concentrations in the uppermost groundwater in sandy areas are falling but they still exceed the standard. The nitrate concentrations in the clay-soil areas are close to standard, and they are well within requirements in peatland areas.
Nitrate concentrations under agricultural land in sandy areas
The nitrate concentrations in the uppermost groundwater under agriculture in sandy areas exceed the standard of 50 mg/l in numerous locations. The nitrate concentrations in the sandy areas have been moving downwards in recent years.
Nitrate concentrations can fluctuate widely from year to year due to differences in precipitation. Once corrected for weather, nitrate concentrations in between 1992-2000 show a downward trend.
Nitrate concentrations under agricultural land in clay-soil and peatland areas
Nitrate concentrations in the clay-soil areas are clearly lower than in areas with sandy soils, although concentrations above 50 mg/l are found in these areas as well. Concentrations are lowest in the peatland areas.
Policy
The World Health Organization (WHO), followed by the EU (in its Drinking Water Directive of 1980) and the Dutch government (in the Water Supply Act), set the Maximum Allowable Concentration (MAC) for nitrate in water for human consumption at 50 mg/l. The EU Nitrate Directive assumes that all water which is a possible source of drinking water must meet the MAC standard. Consequently, the groundwater in the Netherlands must also meet this MAC standard. The directive includes a limit of 170 kg/ha on the amount of nitrogen applied in manure. The Netherlands is implementing the Nitrate Directive in the mineral accounting system (MINAS) and a system of manure transfer contracts. In derogation from the Nitrate Directive, the Netherlands wishes to apply up to 250 kg N/ha from manure to grassland. The European Commission still has to give its approval.
Relevance
The run-off of nitrogen (including nitrate) into groundwater threatens the quality of drinking water. In lower sandy, clay-soil and peatland areas, nitrogen mainly runs off into surface water, as a result of which the water eco-system (including riverbanks) comes under threat. In 1999, the desired quality standard for nitrate in groundwater of 25 mg/l was exceeded at eleven pumping stations. For extraction in the loess areas of South Limburg, the concentration is between 30 and 40 mg/l at several extraction points. Additional treatment measures are required at two pumping stations in order not to exceed the drinking water standard for the water supply (Willems et al., 2002).
