Trends in dissolved organic C (DOC) have been positive in almost all the ICP Waters sites in North America and Europe, beginning in the early 1990s, especially in areas where acid deposition has been considerable. This has lead to a significant browning of surface waters. The extended database compiled by ICP Waters to assess DOC trends is the largest region-wide overview (>500 lakes and rivers in northern Europe and North America) that documents the trends in DOC. The DOC trends are related to declining atmospheric loads of sulphate. The browning of the waters is thus a sign of ecosystem recovery from acidification. In near coastal regions, seasalt deposition also affects DOC concentrations and trends.

Langtjern catchment, Norway. Photo: Thorjørn Larssen