The First Data on the Mineralogy and Geochemistry of the Suspension of Lake Onego

Abstract

Abstract —This paper presents the first data on the mineralogy, geochemistry, and quantitative distribution of suspension determined with the use of sedimentation traps installed in Lake Onego (the exposure time was one year (2019)). The obtained data on the mineralogic and geochemical composition of the recent suspension of the Onego water column are compared with the data for the surface layer of the lake bottom sediments (0–10 cm). Data on the sedimentation rates for the substance determined with the sedimentation traps have been obtained for the first time for Lake Onego. The estimates of the sedimentation rates differ slightly from the results of calculation of the sedimentation rates by radioisotope dating based on the distribution of 210Pb activity in the upper layer of bottom sediments in combination with the data on 137Cs. It has been established that the mineral part of the dispersed sedimentary matter that entered the lake reaches the bottom sediment without significant changes. The geochemistry of the sedimentation traps is similar in many respects to the geochemistry of the upper part of the bottom sediments (0–10 cm) in different areas of Lake Onego. The dispersed sedimentary material and the bottom sediment differ in the amount of the biogenic part (in the bottom sediment layer (0–10 cm), the biogenic part loses a significant part of organic matter). The bottom sediments are characterized by a strong predominance of the ferruginous varieties of illite and chlorite, in contrast to the suspension with the prevailing Mg–Fe varieties of these minerals. Degraded mica minerals brought by rivers are regenerated to normal ferruginous illites and chlorites directly in the uppermost part of the bottom sediments. The bottom sediments are characterized by higher manganese and molybdenum contents, and the material from the sedimentation traps, by high mercury contents.