Contemporary Sedimentation in Lake Onego: Geochemical Features of Water, Suspended Matter, and Accumulation Rate

Abstract

The spatio-temporal variability of the modern sedimentation process in Lake Onego, the second largest lake in Europe, was evaluated. The chemical composition of the lake water was studied. Sedimentation takes place in the oxidation conditions of low TDS water of the calcium bicarbonate type, where the ratio between terrigenous clastic material and lacustrine biochemical suspended matter in the material deposited to the bottom is close to one. We demonstrate that the sedimentation process in the lake is non-uniform. Sedimentation rates in different regions of the lake were estimated (0.1 to 2 kg per sq. m of bottom surface per year) through in situ surveys with sediment traps. Annual sediment input was estimated on the basis of the lake’s chemical balance. Analysis of the qualitative characteristics of the material deposited to the bottom shows its composition corresponds to the humus-Fe-Si type of sedimentation. The uniform texture and mineral composition and the similar multielement spectra of the sediments suggest that active water dynamics cause fine-grained suspended load to remain in the water column for prolonged time periods. Variations in the sediment chemical composition across the lake are due to natural causesand to unevenly distributed anthropogenic pressure.