CHEMICAL WEATHERING OF SILICATE ROCKS IN KARELIA REGION AND KOLA PENINSULA, NW RUSSIA: ASSESSING THE EFFECT OF ROCK COMPOSITION, WETLANDS AND VEGETATION

Abstract

This study is aimed at assessing the effect of factors including lithology, forest/peatland coverage, dissolved organic carbon, and vegetation on chemical fluxes and concentrations of major elements in rivers. The mean annual element concentrations and dissolved fluxes of acid and basic rock dominated watersheds of the Karelia region and Kola peninsula, NW Russia, have been estimated from the chemical composition of river water samples collected in the summers of 1996–2000 and from annual discharge and chemical composition data of 16 watersheds collected from 1961 to 1975. The mean annual flux corrected for atmospheric input varies from 0.5 to 5.6 t/km2/y and is dominated by alkali metals for the Kola alkaline rocks and by calcium for the Karelian granito-gneisses. The pure “granitic” and pure “basaltic” river chemical denudation rates in the Baltic shield are 0.33 and 2.3 t/km2/y, respectively. The cationic and silica fluxes of both granitic and basaltic watersheds are comparable with those of other boreal regions having similar runoff, compositions, and climate. The cationic flux of the rivers is positively correlated with the basic rock fraction of the watershed, whereas the dissolved organic carbon flux increases with the increasing peatland fraction. The chemical composition of the river water is controlled by bedrock dissolution during dry periods, and by plant litter degradation and washout of organic debris from the topsoil horizon during wet periods. Taking account the chemical composition of the plant litter and the biological turnover intensity, it was estimated that the plant litter degradation in Kola and Karelia regions provides 10–40% of total annual dissolved riverine element flux.