Indicator 6.1.b Nitrate in groundwater

6.1.b Nitrate in groundwater

Nitrate (NO₃⁻) are nitrogen compounds that occur naturally in the soil at certain concentrations but also enter the environment through anthropogenic sources. The nitrate content in groundwater is recorded by the Bundesländer for reporting to the European Environment Agency (EEA) on the state of groundwater in Germany. The basis for this is the so-called EEA monitoring network, which consists of specifically selected monitoring sites. This network comprises approximately 1,200 representative monitoring stations. The data are compiled by the German Environment Agency (UBA) based on information provided by the Federal/State Working Group on Water (LAWA).

This indicator shows the proportion of total monitored sites at which the prescribed threshold value was not exceeded. Naturally occurring nitrate in the soil contributes between 0 and a maximum of 10 milligrams per litre to the overall concentration in groundwater. Concentrations between 10 and 25 milligrams per litre indicate a low to moderate level of pollution. Values between 25 and 50 milligrams per litre reflect significant groundwater contamination. If the threshold of 50 milligrams per litre – as stipulated in the Groundwater Ordinance and forming the basis of this indicator – is exceeded, the groundwater is considered chemically impaired and unsuitable for drinking water use without treatment.

Like Indicator 6.1.a on phosphorus concentrations in surface waters, this indicator does not provide information on the degree to which the threshold value is exceeded or undercut. For example, nitrate pollution at individual monitoring points may have decreased significantly – but if concentrations still exceed the threshold of 50 milligrams per litre, this improvement is not reflected in the indicator. Conversely, increasing nitrate concentrations that remain below the threshold are also not taken into account. When interpreting the results, it must also be considered that measures to reduce nitrate pollution often take time to have an effect, as percolating water can take several years to reach the groundwater.

In 2023, the threshold of a maximum of 50 milligrams of nitrate per litre was met at 85.0% of all monitoring sites. Since 2008, the proportion of sites meeting this threshold has remained largely unchanged. As such, the politically defined objective of achieving compliance with the threshold at all monitoring stations has not been met – nor is there any discernible trend towards meeting this goal. At 18.0% of the monitoring sites, nitrate concentrations ranged between 25 and 50 milligrams per litre. Although this refers to values below the threshold, it nonetheless indicates an elevated level of pollution. This proportion has also remained largely stable over the years.

Groundwater contamination with nitrate primarily results from the leaching of nitrate from various nitrogen-containing fertilisers. These include organic fertilisers such as slurry and manure, as well as mineral fertilisers, which are particularly used in intensive arable farming. In recent years, digestate – a by-product of biogas production – has also increasingly been used as fertiliser in agriculture. In all these cases, fertilisation that is not tailored to the actual nutrient demand of crops can lead to elevated nitrate concentrations in groundwater. Consequently, there is a link between the development of the “nitrogen surplus in agriculture” (Indicator 2.1.a) and nitrate contamination of groundwater.

To assess the specific impact of agricultural practices on nitrate pollution in water bodies, separate nitrate reporting to the European Union (EU) is conducted. For this purpose, those monitoring stations within the EEA network whose catchment areas are predominantly used for agricultural purposes are selected. As a result, nitrate concentrations in this specific network are higher than the average value of Indicator 6.1.b.