Nitrate in groundwater

Nitrate is naturally present in groundwater only in low concentrations. Distinct elevated concentrations of more than 25 mg/l nitrate occur nationwide at up to 15% of the monitoring sites sampled. In areas used predominantly for arable farming, the concentrations exceeded this level at up to 60% of the monitoring sites.

In 2013 nitrate concentrations were above the standards of the water protection ordinance (GSchV) of 25 mg/l at 15% of the NAQUA monitoring sites. The limit of tolerance in the Ordinance on Foreign Substances and Constituents in Food (FIV) of 40 mg/l was also exceeded at about 3% of the monitoring stations.

Nitrate concentration in groundwater 2013 and percentage of cropland. Average and maximum values per monitoring site.

Land use

Intensive agriculture is mainly responsible for elevated nitrate concentrations in groundwater. In 2013 the GSchV standards were exceeded at about 45% of the monitoring sites with arable farming as the principle land use. At around 13% of these monitoring sites the FIV tolerance value was exceeded as well.

Temporal changes

Between the mid-1990s and 2002, at a large number of monitoring sites nitrate levels fell by 10% to 20%. In the subsequent years an increase in nitrate levels was observed, especially at monitoring sites located in catchment areas characterised by agricultural land use. Since 2007 nitrate levels have decreased slightly at the majority of monitoring sites.

In addition to agricultural factors such as the application of fertilizers or soil tillage, the amount of precipitation and groundwater recharge also appear to significantly affect nitrate levels in groundwater. While nitrate levels tended to decrease in the wetter years before 2002 and after 2006, they increased, sometimes markedly, during the period between 2003 and 2005 which was drier than average.