Regional accumulation pattern of heavy metals in lake sediments and forest soils in Sweden

Abstract

Concentrations of heavy metals (Pb, Cd, Hg, Zn, Cu) in the mor layer of forest soils and in recent lake sediments from small forest lakes show similar large-scale distributions in Sweden. Comparatively high concentrations of Pb, Hg and Cd are found in southern Sweden, with gradually decreasing concentrations towards the north, indicating a marked impact of long-range transport. In general, for most metals, higher concentrations are found in lake sediments than in the mor layer and also a more marked concentration gradient over the country. This is probably due in part to natural processes but also to an increased leaage in souther SSweden of especially Zn and Cd from acidified forest soils. In southern Sweden, concentrations in the mor layer have probably increased by factors of ∼ 5–10 for Pb and 3–5 for Hg and Cd, compared with estimated pre-industrial values. In sediments, the levels have increased even more. In the northernmost part of the country also, the contents of these metals are enhanced, probably by approximately a factor of 2. Concentrations of Zn and Cu do not appear to have generally increased in the mor layer. Relative increases in mor of Pb and Hg in southern Sweden are above the levels where adverse effects on soil biological processes might occur.