SOURCES OF TRACE-METALS IN STREAMS AND HEADWATER LAKES IN FINLAND

Distributions of Mn, Zn, Cu, Ni, Cr, Pb, As, and Cd in Finnish surface waters were studied by comparing two data sets: samples from 154 head water lakes collected by the Water and Environment Administration in 1 992 and samples from 1165 headwater streams collected during the envir onmental geochemical mapping program of the Geological Survey of Finla nd in 1990. It was expected that headwater takes with catchments small er than 1 km(2) and high lake percentage (ratio of lake area to catchm ent size) would be more influenced by atmospheric trace metal depositi on than the streams, with average catchment size of 30 km(2). The lake s with highest arsenic concentrations lie in an area with greenstones and arsenic-rich black schists. The same lakes have high copper concen trations, which evidently are derived from the Cu-rich greenstones of the catchment. The high copper concentrations of streams and lakes in the industrialized region of the southwest coast are due to several an thropogenic sources. The highest concentrations of chromium occur in b rown stream and lake waters rich in humic matter, while manganese and zinc concentrations, which are controlled by acidity, tend to be eleva ted in low-pH waters. The high nickel concentrations in lakes in south western Finland probably are due to anthropogenic input, while Ni anom alies in stream and lake water in eastern Finland are correlated with high Ni contents of glacial till. The lead concentrations in lakes are mainly of airborne anthropogenic origin. The pattern of atmospheric d eposition is reflected in the concentrations of Cd, As, Cu, Zn, and Ni in headwater lakes, but land-use, the natural distribution of metals in the overburden, water acidity, and the amount of humic substances i nfluence the distribution of trace metals in both lakes and streams. T hus the trace metal distribution in headwater lakes cannot be used alo ne to estimate the contribution of anthropogenic atmospheric depositio n to metal anomalies in Finnish surface waters.