Concentrations of heavy metals in small Norwegian lakes

Abstract

As part of regional surveys of lakes in Norway the concentrations of Zn, Pb, Cu and Cd were measured in surface- and bottom-water samples collected from representative, small, pristine lakes (136 in southern Norway sampled in October 1974, 58 resampled in March 1975, and 77 in northern Norway sampled in March 1975). The lakes, a statistically representative sample of small lakes in Norway, were chosen such that their watersheds are undisturbed. Heavy-metal concentrations in these lakes thus reflect only natural inputs and anthropogenic inputs via the atmosphere. The generally low concentrations (Zn 0.5–12.0 μg l −1; Pb 0–2.0 μg l −1; Cu 0–2.0 μg l −1; Cd 0.1-0.5 μg l −1) measured in lakes in central and northern Norway provide estimates of natural “background” levels. These estimates may be too high because they include the global-scale deposition of heavy metals from the atmosphere which has increased as a result of industrial activities. Concentrations of Zn and Pb in lakes in southernmost and southeastern Norway lie above these “background” levels, apparently because of atmospheric deposition associated with the acidic precipitation that falls over southern Scandinavia. Increased heavy-metal concentrations in acid lakes may also be due to increased mobilization of metals due to acidification of soil- and surface-waters.