Time series of long-term annual fluxes in the streamwater of nine forest catchments from the Swedish environmental monitoring program (PMK 5).

International cooperation has contributed to major declines in SO(2) emission and S deposition during the last two decades in Europe. The chemical recovery from already anthropogenically acidified sites however, has been slow. In the present paper, long-term trends of chemical fluxes from nine selected forested reference catchments were studied, to detect recovery from acidification and leaching of S and base cations (BC). A decline in S deposition resulted in a decreased flux of non-marine sulfate (SO(4)*) in seven of nine streams, with statistically significant changes in four. The two cases with slight increases in SO(4)* flux resulted from increasing water flow. The SO(4)* decrease was followed by a recovery from acidification in terms of increased ANC flux in those sites in southern Sweden that were chronically acidified. The recovery was probably slowed down by leaching of SO(4) from the soil and a decrease in the flux of BC. A better understanding of the processes for leaching of SO(4) and BC is needed in order to quantify the need for further restrictions of sulfur emissions to allow a long term recovery of acidified catchments. The flux calculations available from small catchments such as those in this study, are of value for that understanding.