The map shows the mean annual concentration of total ammonium (TA), expressed as milligrams of N-NH4 per litre of water, observed in river monitoring stations and reported by EEA member countries via WISE. For most countries the mean annual value is based on observations over the whole year, whereas some countries only collect samples during the growing season (due to ice cover in winter).
Total ammonium concentration can increase as a result of discharges from waste water treatment plants, industrial effluents and agricultural runoff. Ammonium exerts a demand on oxygen in water as it is transformed to oxidised forms of nitrogen. It is also an important nitrogenous fertilizer for aquatic plants, so it can cause eutrophication and indirectly reduce the dissolved oxygen due to increased BOD. In addition it is toxic to aquatic life at certain concentrations in relation to water temperature, salinity and pH. For example ammonium hydroxide in water is extremely toxic to fish and aquatic life at elevated pH levels. It can also pollute drinking water and bathing water.
The purpose of the map is to provide an overview of the mean annual value of total ammonium in rivers across Europe and to enable the user to compare values per country or individual monitoring station, depending on the scale of visualisation. Historical data since 1993 can be displayed using the time slider.