The Swedish Throughfall Monitoring Network (SWETHRO)
Since 1985, researchers within the regional environmental monitoring network Krondroppsnätet have followed the development of sulfur and nitrogen deposition and its impact on groundwater quality in Sweden.
Despite the fact that sulfur deposition has decreased sharply since the measurements started in the 1980s, measurements and modeling indicate that the recovery from acidification is slow, and that soil and surface water will be acidified for a long time to come. Nitrogen deposition in the southwestern part of Sweden remains at a level that is probably higher compared with the removal of nitrogen from forest ecosystems in connection with felling, which means that nitrogen is continuously stored in the forest soil. This can in the long run lead to a leakage of mainly nitrate to groundwater and surface water.
Climate change and changed forestry can have major effects on the recovery from acidification and the risk of nitrogen leaching to lakes and watercourses. An increased removal of branches and treetops in connection with deforestation also means that buffering nutrients disappear from the forest ecosystems, substances that would have counteracted acidification if they had been allowed to remain.
National and international standard
The purpose of Krondroppsnätet is to describe conditions, regional differences, development over time and the effects of precipitation of acidifying and eutrophication substances. In addition to the precipitation measurements, soil water chemical sampling and analyzes of air contents on the sample surfaces are also performed. The methodology follows national and international standards. In recent years, different types of model calculations have been developed, which are used in comparison with the measurement results and to produce forecasts and scenarios for the future.
Krondroppsnätets measurements are part of the basis for the regional and national environmental goal work. The work is run by IVL Swedish Environmental Institute in collaboration with Lund University and is primarily financed by various air conservation associations, county administrative boards and the Swedish Environmental Protection Agency.