The map shows the mean annual concentrations of Nitrate (NO3) as mg/L NO3-N measured at WISE SoE river monitoring stations during 2011. For most countries the values are based on measurements over the whole year, whereas some countries have samples only from the growing season (due to ice cover in winter).
The purpose of the map is to provide an overview of the mean annual concentrations of the nitrates in rivers across Europe and to enable viewer to make comparisons of the values in European countries, River basin districts or in individual monitoring sites. High or increased (compared to reference condition) concentration of nitrate represents a risk to normal functioning of downstream coastal ecosystems, causing eutrophication* with potentially excessive growth of algae or other aquatic vegetation, oxygen deficiency in the bottom waters and reduced biodiversity. High concentration of nitrates also represents a health risk if the water is used for drinking water. The WHO guideline for drinking water is < 10 mg/L NO3-N (equivalent to ca. 50 mg/L NO3). For additional information on nutrients in water see the Water quality and pollution by nutrients section of the WISE website. Nitrates in excess can give rise to eutrophication in down-stream coastal waters by stimulating excessive growth of algae and other aquatic plants when nitrogen is the limiting factor for growth.