In Grosser Arbersee, a cirque lake in the Bavarian Forest (Germany), the acidification chronology since the late-glacial period has been studied paleolimnologically, applying subfossil diatom assemblages. Distinct phases of acidification could be detected, both natural phases via postglacial development of soils and vegetation in the catchment, and anthropogenic phases via mineral acid depositions. Whereas the former phases were accompanied (and most probably caused as well) by increases in organic carbon contents, the latter phases are characterized by losses of organic carbon contents from the lake.