Nutrients in watercourses
Nitrate and phosphate in watercourses are good indicators of water pollution by nutrients which is anthropogenic, i.e. caused by human activity. Nutrients enter the water through municipal wastewater or discharge from intensively fertilised agricultural land. A higher nitrate or phosphate concentration does not normally have negative effects in a watercourse, but high phosphate discharges into standing waters can cause eutrophication. Nutrients also pollute the seas into which the rivers flow.
81% of monitoring stations for nitrate and 71% for phosphate are in good or very good condition. Targets are however being exceeded locally in agricultural and developed regions (see map). Problems occur mainly in small streams with a high wastewater content or a high proportion of intensive farming in the catchment. These small watercourses are covered by the NAWA monitoring network.
The fluctuations between years are due to normal fluctuations in the runoff conditions rather than to a change in the pollution situation. As no significant improvement is observed between 2011 and 2018, the evolution of nutrients in watercourses is considered unsatisfactory.
Nevertheless long term time series do indicate that in general water pollution by nutrients has fallen significantly in the last few decades. The reduction in phosphorus content was particularly evident following the ban on phosphates in detergents in 1986. The phosphorus content continued to fall after 1990 due to the progressive expansion of wastewater treatment plants. Efforts in agriculture to reduce diffuse nitrate and phosphorus discharges, e.g. by less nutrient-intensive soil management and WWTP optimisation can contribute to a further reduction in nutrient concentrations in the water.
The water quality is recorded jointly by the federal government and the cantons under the NAWA National Surface Water Quality Monitoring at approximately 120 monitoring stations. The chemical state of the water is evaluated on the basis of the phosphate and nitrate concentration by the method “Physico-chemical surveys, nutrients” in the modular stepwise procedure.