Nitrates Directive Compliance: Checking for Nitrate in Groundwater in the Netherlands
National Institute for Public Health and the Environment
The EU Nitrates Directive states a threshold level of 50 mg/l nitrate in groundwater. In the Netherlands, compliance is currently checked in the upper one meter of groundwater. A draft EU monitoring guideline leaves open the possibility to check compliance in the upper five meters of groundwater. The nitrate concentration in groundwater in the Netherlands has significantly decreased between 1996 and 2004 due to policy measures. Nitrate concentrations are below the EU threshold level in large parts of the Netherlands. In sandy soils, however, the average nitrate concentration still exceeds the 50 mg/l value in the upper one meter of the groundwater. Additional measures are required to meet EU threshold values. Changing the checking level from the upper one meter to the upper five meters of groundwater could provide the Netherlands with the possibility to meet the EU threshold level for groundwater, without having to implement major additional measures by farmers. Nitrate concentrations are likely to decrease with depth because of denitrification. Any adjustment in the compliance checking level requires well-founded data on whether nitrate concentrations actually decrease with depth in the upper five meters of the groundwater. It must also be clear which processes cause the decrease, and in particular whether such an adjustment would result in a shifting of the problems to the surface water. The Nitrates Directive also has targets for surface water quality. A study showed that in sandy soils with relatively deep groundwater tables (i.e. > 1 meter) nitrate concentrations did not decrease with depth in the upper five meters of groundwater. Here, the act of denitrification may be blurred by temporal changes in nitrate leaching from the soil. In sandy soils with high and intermediate groundwater tables (within 1 meter) a decrease in nitrate concentrations with depth was shown. Results indicated that in these soils significant loads of agricultural nitrate are transported into surface waters. Thus, allowing higher nitrate concentrations in the upper groundwater may cause eutrophication of surface waters. The Dutch Parliament introduced a motion in 2009 stating that maintaining the current compliance checking level in the upper one meter of groundwater would result in unfair competition for Dutch farmers. The Dutch Parliament requested the Government to calculate the decrease in nitrate with depth using models and to measure the nitrate concentrations not only in the upper one meter of groundwater, but in the upper second and upper fifth meter of groundwater as well. A new monitoring network to meet the Parliaments request is currently drafted.