Chloride Ion Content in the Water of the Volga River

Abstract

The purpose of the research is to determine the patterns of seasonal variability of chloride ions content in the Volga River water and to quantify the amplitude of inter- and intra-annual variations taking into account years of different water availability. Materials and methods. Systematic hydrochemical observations were carried out on the Volga River during the period 2001-2018. The stationary observation site was located on the left bank of the river, 2.5 km downstream of the Zhigulevsky hydrosystem (the closing section of the Kuibyshev reservoir). Water samples were taken from the concrete wall with Molchanov GR-18 batometer from the surface horizon. The number of samples taken is 216. Mass concentration of chloride ions (Cl-) was determined in accordance with the applicable Roshydromet guidelines. Statistical analysis of water discharge data and concentration of chloride ions was carried out using Statistica software. Results and discussion. The average concentration of chloride ions during the 18-year observation period was 27.0 ± 2.2 mg/dm3. The highest mean annual chloride concentration reached 31.0 ± 2.3 mg/dm3 and the lowest 24.2 ± 2.1 mg/dm3. Chloride content was characterized by a pronounced seasonal variability. During the winter low-water period there was a gradual increase in chloride concentration. The maximum was observed in April, before the spring flood. During the spring flood, chloride concentrations decreased sharply, reaching their lowest values in May at the peak of the spring flood. Their concentration gradually increased during the summer and decreased during the autumn. The seasonal amplitude of chloride concentrations varied from 14.0 ± 1.8 mg/dm3 to 41.3 ± 2.6 mg/dm3. In years of varying water availability, the amplitude of seasonal luctuations can increase or decrease. During the spring flood periods of high-water years, chloride concentrations decreased sharply, while during low-water years they increased significantly. In general, during high-water years the chloride concentration decreased, while during low-water years it increased due to a change in the ratio of surface and groundwater components of water flow formation. Conclusions. When assessing water quality and determining the spatial heterogeneity of chloride ion concentrations, patterns of their seasonal variability must be taken into account.