Long term trends in nitrate in Danish groundwater during the last 70 years

The Danish water supply is solely based on simple treated groundwater, and protection of groundwater has therefore a high priority. At the same time, Danish farming is among the most intensive in the world threatening the... [ view full abstract ]

The Danish water supply is solely based on simple treated groundwater, and protection of groundwater has therefore a high priority. At the same time, Danish farming is among the most intensive in the world threatening the groundwater resources in regard to e.g. nitrate leaching. Numerous waterworks and wells have been closed due to nitrate pollution, and approximately 15% of the area of Denmark has been classified as nitrate vulnerable groundwater abstraction areas.

Since the 1980s, regulations implemented by Danish farmers have succeeded in optimizing the nitrogen (N) management at farm level. The N-surplus (N-output/N-input) has significantly been reduced, the farming N-efficiency has increased, and the N losses to the aquatic and atmospheric environment have been significantly reduced. Accordingly, since the 1980s the overall national upward trend of the nitrate concentrations in oxic groundwater has been reversed. Locally, nitrate trend analyses in monitoring wells have shown a more varied pattern with both upward and downward nitrate trends depending on the age of the groundwater and local agro-hydro-geochemical conditions. Therefore local groundwater protection action plans are being carried out in order to further protect drinking water resources from nitrate pollution.

Strong correlations between nitrate response in oxic groundwater to nitrogen management in Danish agriculture since the 1940’es will be presented.