Seasonal Variability of the Concentration of Chloride Ions in the Water of the Kuibyshevsk Reservoir

Abstract

According to long-term observations in the period 2001–2019. regularities of seasonal variability of the content of chlorides in the water of the Kuibyshev reservoir were studied. Stationary hydrochemical observation point is located in the outlet section of the reservoir. To study the causes of seasonal variability in chloride concentrations, hydrological data were used at the inlet (Cheboksary and Nizhnikamsk waterworks) and outgoing (Zhigulevsk waterworks) sections of the Kuibyshev reservoir. It was found that over the 19-year observation period, the range of seasonal fluctuations in average monthly chloride concentrations was 14–42 mgdm3. Seasonal variability of chloride content is pronounced and is characterized by alternating maxima and minima of chloride concentration. The winter maximum is observed in April before the beginning of the spring flood, and the summer maximum is observed in July before the beginning of the autumn low water. The spring minimum is observed in May at the peak of the spring flood, and the autumn minimum is observed in December before the freeze-up begins. The seasonal variability of chlorides includes four periods (I, II, III, IV), which are formed as a result of the interaction of genetically heterogeneous water masses in the reservoir. Period I is characterized by a gradual increase in the concentration of chlorides due to the inflow of groundwater during the winter low water. The short-term period II is characterized by a sharp decrease in the concentration of chlorides due to the entry of soil-surface waters into the reservoir during the spring flood. Period III is characterized by an increase in the concentration of chlorides due to an increase in the role of soil and groundwater during the summer low water period. Period IV is the longest and is characterized by a gradual decrease in the concentration of chlorides during the autumn low water period. The revealed patterns of seasonal variability of chlorides are unchanged and were observed annually during 2001–2019. However, the values of chloride concentrations significantly depended on the hydrometeorological conditions of a particular year. In dry years, the concentration of chlorides increased, and in high-water years, they decreased in all hydrological seasons of the year.