Geochemical features of river flow into Lake Onego

Lake Onego is the second largest body of water in Europe (S lake mirrors = 9720 km², V = 295 km³, S catchment area = 53100 km²), located at the junction of two geological structures (the Fennoscandian Shield and the Russian Platform) is characterized by a complex morphology of the basin, uneven distribution of river flow and anthropogenic load.

In 2020-2021, the peculiarities of the flow of terrigenous material into the lake, affecting the formation of heterogeneity in the composition of the mineral part of the bottom sediments, were studied. New knowledge was obtained about the seasonal variability of the geochemical composition of river waters, the spatial and temporal nature of its variability was shown. By the example of iron, manganese and total phosphorus, the seasonal distribution of the forms of migration of these elements in rivers is considered. Concentrations of dissolved and suspended forms of trace elements in river waters were obtained. The uneven distribution of river suspension particles by size and degree of rolling, as well as seasonal differences in the ratio of mineral and organic components of the suspension are shown. The study of the composition of the dispersed sedimentary matter revealed similar spectra of minerals. It was found that the material of river suspensions is represented by a biogenic X-ray amorphous mass (biodetrite of diatoms, spores and pollen of plant communities) with associations of detrital mineral particles, scaly formations of layered silicates and aluminosilicates, fouling with jelly-like clots and films of oxides and hydroxides of manganese and iron on organic skeletons.

The study was supported by RFBR grant #19-05-50014, RSF research project #18-17-00176 and by the Federal Budget, within the State Assignments nos. 121021700116-6.