The relative importance of acidity sources for humic lakes in Norway

Abstract

The possible role of natural processes contributing to lake acidification and the occurrence of acidic lakes pH<5) has received considerable attention1–7, but there has been no direct test of the importance of some of the postulated natural processes in Scandinavia where large numbers of acidic lakes occur. Some authors have argued that lakes were acidic simply because of processes occurring in acid soils, and that the effects of acidic precipitation on these lakes were thereby overestimated1,2. We present here an analysis of the role of strong and weak acids in the acidity status of moderately humic lakes (total organic carbon (TOC) 2–15 mg 1−1) in two areas of Norway. The two areas received precipitation with differing acidity and amounts of sulphate. Our data suggest contributions by organic acids to acidity, but strong acids associated with sulphate further reduce the pH and explain the recent acidification of coloured lakes in southern Norway.