Assessment of the Chemical Water Status: Nitrite

Within the National Surface Water Quality Monitoring Programme (NAWA), water quality is recorded jointly by the federal and cantonal authorities at around 100 monitoring stations. The chemical water status is assessed on the basis of the nitrite concentration by the “Physicochemical Water Quality, Nutrients” method in the Modular Stepwise Procedure (www.modul-stufen-konzept.ch). Nitrogen is an essential nutrient for aquatic organisms. Most of the inorganic nitrogen present in surface waters is in the form of nitrate. Anoxic conditions can lead to the formation of nitrogen compounds reduced from nitrate, e.g. nitrite (NO2-). Nitrite is highly toxic to fish, particularly salmonids.