Nitrate concentrations in groundwater are correlated with the nitrogen surpluses at the soil surface. In the Netherlands, both nitrogen surpluses of agricultural land and nitrate concentrations in the groundwater of sandy soils are high. At present, nitrate concentrations in the groundwater of sandy soils exceed the 1980 EC Directive on the Quality of Water Intended for Human Consumption by a factor of 1 to 5. This paper discusses the effects of a series of policies and measures launched by the Dutchgovernment from 1986 onwards to decrease nitrogen losses to acceptable levels. Main focus is on the nitrogen and phosphorus accounting system MINAS, which will be implemented from 1998 onwards. The possible effects of the MINAS policy and measures on thenitrate contamination of groundwater have been examined via whole-farm analyses and simulation models, with a main focus on the nitrate leaky sandy soils and dairy farming systems. With MINAS, all farmers have to account for the nitrogen and phosphorus that is entering and leaving the farm. Further, MINAS includes charged and levy-free surpluses. The height of charges and the height of the levy-free surpluses together regulate the actual nitrogen surpluses at the farms. Levy-free nitrogen surpluses willbe lowered step-wise to 100 kg for arable land and 180 kg per ha for grassland in 2008. Following the implementation of the series of policy measures in the late eighties, data statistics indicate that the nitrogen surplus decreased from a mean of 347 kgper ha agricultural land 1985 to a mean of 299 kg per ha in 1995. Following the implementation of MINAS, our model predictions indicate that the nitrogen surplus at farm level will decrease further to a mean of 147 kg per ha in 2008, i.e. a reduction of 58% with reference to 1985. Mean nitrate concentrations at the average lowest groundwater level will decrease by 60%. Ultimately, 12% of the agricultural land (on sandy soils) will still have a nitrate concentration in the groundwater of more than 50 mg per litre. Our results indicate that MINAS is effective; they also indicate that additional measures are needed for agricultural land on dry sandy soils.
- groundwater pollution
- government policy