Freshwater - State and impacts (Denmark)

The ecological quality of the Danish lakes is controlled by nutrients. A significant decrease in the load of nutrients has been observed since the 1990s. The average level of phosphorus and nitrogen in Danish lakes has decreased by 26 % and 18 % respectively from 2000 to 2008. This has led to a significant improvement in the ecological quality in many Danish lakes, such as improvements in the water turbidity and better conditions for the bottom vegetation.

Figure 1 (3.1.1): Development of the concentration of phosphorous, nitrogen and chlorophyll-a (indicator for algae growth) in 19 Danish lakes. Source: National Environmental Research Institute.

Figure 2 (3.1.2): Development in the water turbidity in 20 Danish lakes. Source: National Environmental Research Institute.

In 2008, the water quality in 54 % of the Danish rivers was classified as good or very good, compared to 42 % in 2000. However, pesticides are measured in 70 % of the monitoring water samples. The improvement in the ecological quality of rivers is mainly due to better sewage treatment and a more careful physical maintenance.

Figure 3 (3.2.1): Development in the ecological quality (Danish River Fauna Index) in Danish rivers. Measurements are from approximately 250 stations in a wide range of small and larger rivers. Source: National Environmental Research Institute.

Figure 4 (3.2.2): Concentration of nitrogen in rivers grouped after the dominant nitrogen source, i.e. aquaculture, agriculture, nature and waste water treatment plants (WWTP). Source: National Environmental Research Institute.

Figure 5 (3.2.3): Concentration of phosphorous in rivers grouped after the dominant phosphorus source, i.e. aquaculture, agriculture, nature and waste water treatment plants (WWTP). Source: National Environmental Research Institute.

Pollution with pesticides and nitrate in groundwater wells closes between 25 and 150 drinking water wells every year. The frequency of pesticides in groundwater drillings has increased since 2000. In 2008 pesticides were detected in 40 % of the drillings from the surveillance programme, and in 11 % of the drillings the concentration of pesticides was above the limit value of 0.1 mg/l. In approximately 17 % of the drillings the concentration of nitrate was above the limit value. Groundwater drillings for drinking water, where concentrations of pesticides or nitrate are above the drinking water limit values, are often closed.

Figure 6 (3.3.3): Pesticide concentration in public groundwater wells. Criteria for including wells in the data are that pesticides are detected more than once from 1993-2008. Source: Geological Survey of Denmark and Greenland (GEUS).

Figure 7 (3.3.4): Concentration of nitrogen in groundwater wells. Data are from 2003-2008.

Source: Geological Survey of Denmark and Greenland (GEUS).