Formation of the Chemical Composition of the Waters of Small Rivers of the Volga Basin in the Tver Region in the Summer

The investigation of natural processes of the chemical composition formation of river waters and the influence of anthropogenic factors on them remains an urgent task of hydrochemistry. In July 2021, a water quality assessment was carried out based on hydrochemical indicators of the upper reaches of 29 small rivers of the Volga River basin within the Tver region. The position of most of the ranges is chosen, if possible, in homogeneous landscape conditions of catchments minimally affected by economic activity. The obtained characteristics can be considered as close as possible to the natural background indicators for the summer low water period. The analysis of spatial differentiation of natural factors was carried out on the basis of landscape maps, geochemical and hydrogeological cartographic materials published different years. The dataset of hydrochemical characteristics was processed using two variations of the hierarchical cluster analysis method. Significant spatial differentiation of the chemical composition of waters has been revealed, and landscape diversity does not play a clear determining role. The chemical composition of water in small rivers is mainly influenced by two factors. The high waterlogging of the catchment leads to an increase in concentrations of Fe, organic matter, phenols and color of the surface waters. The presence of channel lakes negates this factor, which is most noticeably manifested in the association of river waters of the Volga and Selizharovka. The second factor is the recharge by deep groundwater, which increases the mineralization of river waters, the content of basic ions, F, Sr, P, and the leaching of silicates from bedrock. The combined influence of both factors seems to determine the high concentrations of manganese in the region.