Taken from the official translation of the German Sustainable Development Strategy
The nitrate content in groundwater is collected by the Länder for the purpose of reporting on the status of groundwater in Germany to the European Environment Agency (EEA). The monitoring sites used for this purpose together form the so-called EEA monitoring network. The EEA monitoring network comprises a total of 1214 monitoring sites and provides a representative picture of Germany. The data are compiled by the Federal Environment Agency from information provided by the German Working Group on Water Issues of the Länder and the Federal Government (LAWA).
Like the indicator of phosphorus content in flowing waters, the nitrate indicator does not reveal how far above or below the threshold the readings have been. The indicator merely records how many of all the monitoring sites complied with the prescribed threshold. The nitrate load may have fallen sharply at some monitoring sites. Nevertheless, if the concentration remains above the maximum of 50 mg/l, the reduction will not be reflected in the indicator.
The same applies to nitrate loads that have increased but are still below the threshold. The interpretation must also take into account that measures to reduce nitrate pollution may have a delayed effect, since the period of infiltration from the surface to the groundwater can take several years.
The naturally occurring level of nitrate lies between 0 and 10 mg/l. Concentrations between 10 and 25 mg/l indicate minor to medium loads. Concentrations between 25 and 50 milligrams per liter indicate severe groundwater contamination. Figures above the threshold of 50 mg/l which is set in the Ground Water Ordinance and which also underlies this indicator mean that the groundwater has a poor chemical status and cannot be used as drinking water without treatment.
In 2018 the target of less than 50 mg of nitrate per litre was met at 82.7 of all monitoring sites. Since 2008, the percentage of monitoring sites at which this target is met has remained virtually unchanged. This means that the goal of recording concentrations below the threshold at all monitoring sites has not been achieved and that the indicator value is not recognisably moving in that direction. Conversely, in 2018 the nitrate threshold of 50 mg/l was exceeded at 17.3% of the groundwater monitoring sites in the EEA monitoring network. Consequently, the groundwater at these locations cannot be used for drinking-water supplies without treatment. At 17.3% of the monitoring sites the nitrate value lay between 25 and 50 mg/l, which still indicates an elevated degree of pollution. This percentage rate also remained virtually unchanged over the years.
The pollution of groundwater with nitrate is caused primarily by the leaching of nitrate from various nitrogen fertilisers. Besides farmyard manures such as liquid manure and slurry, these also include the mineral fertilisers that are used in intensive crop-farming. The last few years have also seen an increase in the use of digestate, which occurs as a by-product of biogas power plants, as an agricultural fertiliser. All of these things can contribute to higher nitrate values in groundwater if fertilisation is not matched to specific crop requirements. Accordingly, the development of indicator 2.1.a – Nitrogen surplus in agriculture – influences the nitrate load in groundwater.
In order to measure the actual influence of agricultural activity on the nitrate load of waters, there is a separate system of nitrate reporting to the EU. For this report, the monitoring sites for waters in predominantly agricultural catchment areas are selected from the EEA site network. The nitrate load in that specific part of the monitoring network is therefore above the average for indicator 6.1.b.