Glacial lakes often appear turquoise, algae-rich waters are green. But why are a number of rivers and lakes becoming browner and browner? Researchers first observed this process in Scandinavia and Canada. The countries are located in the cold-temperate climate zone and are more affected by global warming than temperate climate zones. When bodies of water turn brown, numerous animal species cannot survive in them. In addition, the drinking water becomes undrinkable.
The brown color is due to the input of more organic material. Especially during heavy rainfall, which occurs more frequently as a result of climate change, carbon is washed out of the surrounding soil and thus ends up in surface water. The phenomenon of water browning is now so widespread that it was included in the status report of Working Group II of the Intergovernmental Panel on Climate Change in 2022.
Water bodies in Germany are also affected by climate-related browning
The German-Swedish Earth system scientist Gesa Weyhenmeyer was among the first to link this phenomenon to climate change. Their 2015 study is featured prominently in the IPCC report. She says: “Areas in which it is getting warmer but not drier are among the risk areas.” These include above all regions in Sweden, but areas in Germany are also affected. Weyhenmeyer warns that if climate change continues, lakes and rivers will increasingly brown: “If the climate gets warmer, more organic material will be decomposed. It can then get into the waters more easily.« Whether and to what extent a body of water changes color depends on land use, air temperature and precipitation.
Scandinavian scientists have also discovered in recent years that the browning favored by climate change also has far-reaching effects on the ecosystem of rivers, lakes and floodplains: the water is becoming warmer and warmer as a result of the discoloration because it absorbs the sun’s rays instead of letting them in reflect. This has consequences for the animal world. Habitats change. Locally, this can contribute to the extinction of animal species.