Nitrate exceeds the limit value of 25 mg/l in groundwater at 18% of monitoring sites across Switzerland. In areas where arable farming is predominant, concentrations are now above the limit at more than 50% of monitoring sites.
Groundwater contains very little nitrate naturally. For groundwater used for drinking water or intended for such use, the Waters Protection Ordinance (WPO) prescribes a limit value ('numerical requirement') of 25 milligrams per litre (mg/l). In recent years, this limit has been exceeded at 18% of NAQUA National Ground Monitoring sites nationwide.
Nitrate levels in arable areas continue to rise
Elevated nitrate concentrations in groundwater are mainly due to intensive agriculture. In areas used primarily for growing arable crops or vegetables, more than 50% of monitoring sites exceed the limit value of 25 mg/l. On the Swiss Plateau concentrations are above 10 mg/l at 80% of monitoring sites.
Although there was a slight decline in nitrate concentrations until 2016/2017, concentrations have since been increasing at many monitoring sites. This increase is particularly pronounced in areas with vegetable crops and arable land, where there is a lot of excess nitrogen in the soil. In these areas, levels have increased for five years in a row.
Both hydrological and various agronomic factors are possible drivers of the increase of the nitrate concentrations under cropland. Clarifications are underway.
Last modification 02.06.2023