Water quality and pollution by nutrients

The overloading of seas, coastal waters, lakes and rivers with nutrients (nitrogen and phosphorus) can result in a series of adverse effects known as eutrophication.

In severe cases of eutrophication, massive blooms of planktonic algae occur. Some blooms are toxic. As dead algae decompose, the oxygen in the water is used up; bottom-dwelling animals die and fish either die or leave the affected area. Increased nutrient concentrations can also lead to changes in the aquatic vegetation. The unbalanced ecosystem and changed chemical composition make the water body unsuitable for recreational purposes and other uses, such as fish farming. The water becomes unsafe to drink.

Many societal activities result in nutrients being discharged into the aquatic environment, e.g. through wastewater from households and industry or by loss of nutrients from agriculture and fish farming. In some areas, atmospheric deposition of nutrients can also play a role. Agriculture is the main source of nitrogen loading and a major source of phosphorus loading, although much phosphorus also comes from point sources and sparsely built-up areas.

The effects of excessive nutrient loading are especially noticeable in the groundwater (nitrate), in lakes (phosphorus), large slow-flowing rivers and in the estuaries, coastal waters as well as open marine waters. Much of the nutrient input to the lakes and the coastal waters comes from rivers.

Phosphorus concentrations generally decreased in European rivers and to a lesser extent lakes during the 1990s, reflecting the improvement in wastewater treatment over this period. Overall, there has been a minor decrease in nitrate concentrations in European rivers over the same period, but there is no evidence of a decrease (or increase) of nitrate concentrations in Europe’s groundwater and lakes.

 
Nitrate and phosphorus concentrations in freshwater bodies between 1992/1996 and 2004.

Notes: Numbers of groundwater bodies, lake and river monitoring stations in brackets

Lake: nitrate data from Estonia (4 stations on 1 lake), Finland (6 stations on 6 lakes), Germany (5 stations on 5 lakes), Hungary (15 stations on 6 lakes), Latvia (1 station on 1 lake) and Slovenia (4 station on 2 lakes).

Total phosphorus data from Austria (5 station on 5 lakes), Denmark (19 station on 19 lakes), Estonia (4 station on 1 lake), Finland (11 station on 11 lakes), Germany (5 station on 5 lakes), Hungary (11station on 2 lakes), Latvia (1 station on 1 lake), Sweden (3 station on 3 lakes) and Slovenia (4 station on  2 lakes).

Groundwater bodies: 147 groundwater bodies with data from Austria, Bulgaria, Denmark, Estonia, Finland, Germany, Lithuania, the Netherlands, Norway, Portugal, Slovak Republic, Slovenia and United Kingdom

Rivers: data from Austria, Bulgaria, Czech Rep., Denmark, Estonia, Finland, France, Germany, Hungary, Latvia, Lithuania, Poland, Slovak Rep., Slovenia, Sweden and United Kingdom.

Concentrations are expressed as median of annual average concentrations for groundwater, rivers and lakes.

Data are from representative river and lake stations. Stations that have no designation of type are assumed to be representative and are included in the analysis.

Source: EEA CSI20

 
For some countries there have been significant decreases in river nitrate concentrations (Figure Trend_NO3). Denmark and Germany had the highest proportion of river stations with decreasing trends indicating that national and EU measures introduced to reduce nitrate pollution, such as those in the Nitrates Directive, are taking effect. Also the Czech Republic, Latvia, Hungary and Poland had a high proportion of river stations with decreasing levels of nitrate.  These decreasing nitrate levels are likely to be due to the decrease in agricultural activities that has taken place in these countries during their transition to a market-oriented economy. 

Trend_NO3: Percentage of river monitoring stations per country with upward or downward trend of nitrate concentrations during the period 1992 to 2004

Note: Negative values on ‘y’ axis equates to downward trends, positive values to upward trends.

Analysis based on representative river monitoring stations except for Norway where for rivers flux monitoring stations were used. Source: EEA CSI20

Further information on nutrients in surface waters can be found in the EEA core set indicator on nutrients in freshwater

 
Publications and links

EEA 2005: The European environment - State and outlook 2005. Part A: Integrated assessment, chapter 5 Freshwaters, and 6 Marine and coastal environment

EEA 2003: Europe's water: An indicator-based assessment. Topic report No 1

EEA 2000: Nutrients in European ecosystems. Environmental assessment report No 4

CEC DG environment homepage on the Nitrate Directives

WHO and CEC 2002: Eutrophication and health