ABSTRACT
ABSTRACT: In the Netherlands, eight out of twelve provinces have both soil and groundwater quality monitoring networks. The effects of (changing) land use practices are evaluated by monitoring temporal and spatial trends in soil and groundwater quality. The soil quality monitoring networks focus on the upper metre of the soil and groundwater. The groundwater quality monitoring networks focus on groundwater at depths from about 5 to 30 metres. In this research, data of both soiland groundwater monitoring networks are made comparable and evaluated together. In this way it is possible to present detailed concentration-depth profiles for areas with common characteristics. The results show that the nitrate concentration-depth profile is related to the combination of soil type, land use and hydrological situation. Nitrate is present in low concentrations in shallow groundwater of clayey and peaty soils, while it is absent in the deeper groundwater of these areas. In shallow groundwater of sandy soils with agricultural land use, nitrate concentrations are high and often exceed the EU nitrate directive of 50 mg 1-1. However, the deeper groundwater of sandy soils with agricultural land use in recharge areas (dry anthrosols and podzols) shows much higher nitrate concentrations than the deeper groundwater in groundwater discharge areas (wet anthrosols and podzols). This is related to the older age of the deeper groundwater in discharge areas, which mostly is above 50 years. Around 1950 agricultural practices were rather different and manure loads in the recharging groundwater were much lower. The results also show that two provinces with similar site characteristics but different manure loads have a similar nitrate concentration-depth profile. This is related to regional differences in geochemical characteristics of the deeper aquifers, which cause nitrate reduction in one province, but not in the other.
