SOURCES OF ACIDITY IN RUNNING WATERS IN CENTRAL NORTHERN SWEDEN

Factors controlling the acidity of running waters between the coast of the Gulf of Bothnia and the Caledonian mountain range in central-northern Sweden were studied intensively in 8 large streams and in two synoptic surveys of 179 small streams. The bulk deposition of SO42- was between 11-22 mu eq m(-2) y(-1), of which 93% was nonmarine, with the highest values in the coastal region. Organic anions were the most frequent acid anions in the whole investigation area followed by sulfate. The major portion of SO42- was from natural sources in the whole investigation area. The most acidic streams occurred in the hilly wave-washed terrain of the coastal region, because of a high terrestrial export of organic acids and very low neutralizing capacity. It is concluded that most of the acidity in the investigated streams is due to natural sources.