ATMOSPHERIC SULFUR DEPOSITION AND STREAMWATER QUALITY IN FINLAND

The correlation between sulfate concentrations in Finnish headwater st reams and atmospheric sulfate deposition has been studied by using dat a from the streamwater chemistry in August-September 1990 and computed S deposition from the anthropogenic emissions. The sulfate concentrat ions and acidity in water are interpolated and smoothed into a deposit ion model grid. These data are compared with geological and pedogeoche mical (glacial till) background information. The areas where the strea mwater SO4 concentrations are mainly controlled by either anthropogeni c S deposition or sulfur in till is estimated by applying the fuzzy Gu stafsson-Kessel algorithm, which provides a soft clustering suitable f or overlapping control factors. Residual areas can be well explained b y the SO4-rich Littorina clay deposits. The higher overall background SO4 concentrations in streams in south Finland compared with central a nd northern Finland are an indisputable consequence of the heavier S d eposition load in the south. However, anthropogenic sulfur deposition has a clear correlation with the sulfates in streamwaters only in nort heastern Lapland impacted by the large industrial emissions in the Kol a Peninsula. The secondary sulfide and sulfate minerals of marine Litt orina sediments are dominating sources in the broad coastal belts, as are the primary sulfide minerals locally in the Pori-Vammala area, at the eastern end of the main sulfide ore belt between Lake Ladoga and t he Gulf of Bothnia, in the Outokumpu area, and in the Perapohja and ce ntral Lapland schist belts. Consequently, in addition to the anthropog enic deposition, there are natural sources of sulfur which cause acidi ty of streamwaters.