Press release 2017-10-11

Why are Swedish lakes turning brown?

Lakes and streams are turning browner. In a new report to the Swedish Agency for Marine and Water Management, researchers at IVL Swedish Environmental Research Institute have summarized about a hundred Swedish studies investigating the mechanisms behind this phenomenon, and how it in turn affects the ability to assess the acidity in our lakes.

– Going back fifteen, twenty years ago, dissolved organic carbon has increased in lakes and streams, making them more brown. This is a concern mainly for water treatment plants. The coal also binds to substances like heavy metals, making it even more difficult to treat, says Filip Moldan, researcher at IVL Swedish Environmental Research Institute.

The trend of brown lakes has been investigated by researchers for many years in both Europe and North America. There are also a number of different theories to what lies behind: climate change, proximity to coniferous forests, changing land use and reduced acidification.

Filip Moldan and co-author Johanna Stadmark believe that all explanations can be correct, but that they have different significance for different periods and regions.

– The trend cannot be explained in general with only one mechanism that would be dominant throughout the whole period, a period which is characterized by varying depositions, weather and land use. For example, the declining sulphur deposition in the nineties was probably the most important factor during that period, says Johanna Stadmark.

Download the report here (Swedish)

For more information contact:

Johanna Stadmark, johanna.stadmark@ivl.se, tel. 010-788 67 68
Filip Moldan, filip.moldan@ivl.se, tel. 010-788 67 81