Impact of acid sulfate soils on stream water geochemistry in western Finland

The influence of acid sulfate soils on stream water geochemistry was studied in thirteen catchment basins in western Finland. Seventy-four unfiltered stream water samples were collected in October 1991 and were analyzed for 29 elements. The occurrence of clay/silt sediments in the catchments was used as an estimate of the occurrence of acid sulfate soils, because the development of acid sulfate soil is extensive from this overburden type. The median pH of the water samples was found to be low, and the median concentrations of several elements, including Al, Co, Li, Mn and Ni, are much higher than those in headwater streams of Finland and in Fennoscandian rivers. High correlation coefficients were found between the percentage of clay/silt sediments in the catchments and the concentrations of Al, B, Be, Ca, Cd, Co, Ni, K, Li, Mg, Mn, Na, (SO42-), Sr, U and Zn in the stream waters, indicating extensive leaching of these elements from the acid sulfate soils. There are also indications of stronger leaching of Cr, Si and T1 from the acid sulfate soils than from other soils. The concentrations of As, Fe, Pb, Sb and V vary independently of soil type. Only one element, V, shows a positive correlation with the content of total organic carbon, which was analyzed in 10 water samples.