SEASONAL VARIABILITY OF SEDIMENTATION FLOWS IN SALT MEROMICTIC LAKE SHIRA (KHAKASSIA)

The relevance of the work is caused by the need to study seasonal variations in the volume and composition of sedimentation flows in modern lakes and their relationship with weather and climatic factors, which can serve as a basis for reconstructing climatic changes in the past. The main aim: to assess seasonal changes in the mass, velocity and chemical composition of sedimentary material entering Lake Shira on the basis of generalization and analysis of the results of multiyear annual monitoring of the material of sedimentation traps incubated in the lake. Object of the study was the drainless, slightly saline meromictic lake Shira, located in the steppe intermontane depression on the territory of the Republic of Khakassia. Methods: long-term seasonal monitoring of sedimentary material forming bottom sediments using sedimentation traps incubated in the lake; study of the obtained material for a wide range of parameters (biological, hydrochemical, lithological-geochemical, granulometric, etc.) by various conventional methods, including the method of X-ray fluorescence microanalysis on synchrotron radiation beams (XRF-SI), adapted for the study of bottom samples; computer statistical analysis of the data obtained (multiple regression method, cross-correlation analysis, etc.) in order to identify the relationship between regional temperatures and the chemical composition of the deposited material with the construction of a regression model. Results. Based on the study of the amount and elemental composition of the sedimentary material of the seasonal bottom traps of Lake Shira, collected for 2012–2017, a dynamic model of the seasonal influx of sedimentary flows in lakes of this landscape-geochemical type was formulated. It has been established that the most intensive sedimentation of the material occurs in the summer-autumn period, less – in the winter-spring period. At the same time, in spring, the accumulation of allochthonous (terrigenous) aleurite material, supplied with flood waters, predominates; in the summer-autumn period, simultaneously with the deposition of clastogenic pelitic material, biogenic and chemogenic materials are accumulated in sediments in large quantities. In winter, clastogenic and biogenic processes of sedimentation practically stop, only chemogenic sedimentation of carbonates is observed. It was established that the sedimentation of allochthonous material entering the reservoir occurs during two–three months, which indicates a certain inertness of sedimentation. The presence of a stable relationship between the mass and chemical composition of terrigenous material entering the lake with the regional temperature of the near-surface air, which is one of the main regulators of the water balance of the reservoir, is shown.