Large scale patterns of chemical recovery in lakes in Norway and Sweden:: Importance of seasalt episodes and changes in dissolved organic carbon

Trends from 160 lakes in Norway and Sweden for the period 1990-2004 reveal that Scandinavian lakes show clear signs of recovery from acidification. Sulphate has decreased and ANC, alkalinity and pH have increased. During the last 5 a, the decline in SO4- has ceased, whereas ANC continues to increase. The results also show decreasing trends for Cl, while Na shows no or very small trends. The increase in the Na/Cl-ratio explains part of the increase in ANC. On average for the period 1990-2004 the decrease in Cl contributes 20-50% of the increase in ANC. The main cause of the trends in Cl in southern Sweden and Norway are probably due to declining seasalt inputs due to a higher frequency of heavy storms in the late 1980s and early 1990s. TOC exhibits increasing trends in regions with median TOC concentrations > 3 mg C/L, however, this does not contribute significantly to the observed increase in ANC. (c) 2007 Elsevier Ltd. All rights reserved.