Nitrate in groundwater
Groundwater contains only a few milligrams of nitrate per litre from natural sources. The majority of nitrate in groundwater is released from manure and mineral fertilisers in agriculture. If more fertiliser is applied than the plants can take up, the excess nitrogen is washed out of the soil as nitrate and transferred to the groundwater with the leachate. Deposits of nitrogen oxides and ammonia from the atmosphere also increase the nitrogen content in the soil and therefore the risk of nitrate leaching into groundwater.
Groundwater is Switzerland’s main drinking water resource. Over 80% of Swiss drinking water is extracted from groundwater.
The nitrate concentration in groundwater exceeds the numerical requirement of the Waters Protection Ordinance (WPO) of 25 mg/l nationwide at significantly more than every tenth NAQUA monitoring sites. The nitrate concentration is highest in intensively farmed regions. Below arable land it exceeds 25 mg/l at almost 40% of monitoring sites. Despite a slight decrease in the nitrate concentration at individual monitoring sites, the values are still too high in many places, especially in the Central Plateau.
A balanced nitrogen budget in agriculture and sustainable soil management well adapted to the local conditions would prevent excessive nitrate leaching. Further targeted measures to reduce the nitrate concentration in groundwater are being promoted by the federal government as part of the rehabilitation project according to Article 62a of the Waters Protection Act.
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Since target values can differ from country to country, the data cannot be directly compared.
The nitrate concentration in Swiss groundwater is recorded at national level under the NAQUA National Groundwater Monitoring. The NAQUA monitoring network is operated by the FOEN in close cooperation with the cantonal authorities. The monitoring network covers more than 600 monitoring sites, including 545 for groundwater quality monitoring. The maximum value per NAQUA monitoring site per year is used for the statistical analyses.