Nitrogen and phosphorus in rivers

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Large inputs of nutrients arising from human activities into rivers can lead to eutrophication, adversely affecting the ecology and limiting the use of rivers for drinking water abstraction and recreation. Nutrients occur naturally but it is difficult to determine precise background concentrations for different types of river. Generally background concentrations for phosphate are approximately 10 µg/l as P and for nitrate are between 0.4 to 4 mg/l as NO₃.

In western Europe and accession countries, nutrient concentrations are above these background levels. In the case of phosphate, concentrations above background levels may be having significant impacts on the ecological status of many rivers, particularly as phosphorus is the limiting nutrient in many freshwater systems. The concentrations of phosphate have decreased in western and accession countries in the 1990s, and in northern Europe are close to background levels.

The concentrations of nitrate are highest in the rivers of western Europe where agriculture is the most intensive, and lowest in northern Europe where concentrations are within background ranges. Concentrations in the accession countries are above background levels and have remained relatively unchanged throughout the 1990s. Concentrations in western Europe have remained relatively stable throughout the 1990s.

Nitrate concentration increases are evident in four rivers for which there is a long time series available. These are the river Rhine (which has shown recent decreases in concentrations), the River Ythan and the River Tyne in Scotland and the River Seine in France.