Changes in the concentration of sulfate ions in the Volga water (section of the Zhigulevsky hydroelectric complex)

Abstract

In water bodies, sulfate ions play an important role in the sulfur cycle and affect the state and functioning of aquatic ecosystems. In the Volga water, sulfates rank second among the main anions in terms of their contribution to water mineralization. The concentration of sulfates does not remain constant, but changes continuously throughout the year. For a quantitative assessment of changes in the concentration of sulfates on the Volga River in the section of the Zhigulevsky hydroelectric complex, an analysis of long-term data of hydrological and hydrochemical observations was carried out. For the period 2001-2018 the average annual river flow was 7,7 thousand m3/s. The highest flow rate was observed in 2005 and amounted to 9,0 thousand m3/s, and the lowest in 2011 – 6,2 thousand m3/s. The average annual concentration of sulfates was 55 mg/dm3, the highest – 64 mg/dm3, and the lowest – 45 mg/dm3. The sulfate content was characterized by significant seasonal variability. During the winter low-water period, the highest concentrations of sulfates were observed with a maximum in April, before the beginning of the spring flood (67 mg/dm3). During the flood, the content of sulfates decreased, reaching the lowest values during the summer low-water period in August (44 mg/dm3), and then, from September, the concentration of sulfates gradually increased to 57 mg/dm3 at the beginning of the winter low-water period. Over the 18-year observation period, the amplitude of sulfate concentrations was 34-87 mg/dm3. Seasonal changes in the content of sulfates in the section of the Zhigulevskaya hydroelectric complex are mainly due to the change in water masses formed on the overlying reservoirs as a result of the interaction of the surface and underground components of the water runoff. In dry years, the content of sulfates increases, and in high water, it decreases. The difference in the content of sulfates in extremely high-water and low-water years can reach 15-20 mg/dm3.