INFLUENCE OF ABNORMALLY HIGH WATER TEMPERATURE ON THE HYDROCHEMICAL REGIME OF THE MOUTH AREA OF A SMALL RIVER (BY THE EXAMPLEOF THE RYBINSK RESERVOIR INFLUENCE)
Authors: Otyukova N. 
Published: January 2022

The increase in water temperature in the summer of 2010 affected the change in some hydrochemical characteristics in the water of the mouth area of the river. Ild, a tributary of the Rybinsk Reservoir. The maximum water temperature in the studied area was recorded in May and the second half of summer 2010. A high significant correlation between temperature and organic matter indicators was noted. During the period of maximum warming up in 2010, the total amount of organic matter, its labile fraction, and suspended solids were significantly higher than the period close to the long-term average. A large amount of atmospheric precipitation in June 2010 determined the maximum concentrations of OM, total and dissolved iron. The organic matter is represented mainly by freshly formed compounds, the suspended form of iron prevails over the dissolved one. The organic nature of iron in water is evidenced by a significant correlation between iron and OM in both years studied, r = 0.89–1.0, p <0.05. At the same time, temperature anomalies did not affect the content of dissolved oxygen and an increase in water salinity. The macrocomponent chemical composition of the water in the studied areas is dominated by hydrocarbonate ions, calcium and magnesium ions. In 2009, the relative content of HCO3 and Mg from the section of the free flow of the river to the reservoir is higher than in 2010. At the same time, the relative content of SO4, Cl, and Ca ions, on the contrary, is lower. From spring to autumn, a tendency towards a decrease in the relative content of HCO3 in both studied years was noted in the entire studied water area. The content of hypothetical salts NaHCO3 and MgHCO3 in 2009 exceeded those in 2010 by 3.4 and 5.0 times, respectively. In zones I – IIc, the content of calcium ions is 1.5–2.0 times higher than that of magnesium in 2009, and in 2010, 1.7–2.4 times. In the deep-water section of the reservoir in both years under study, the concentration of calcium ions is, on average, 2 times higher than that of magnesium. In both studied years, the potassium content in the studied water area is noticeably lower than the sodium content. During the spring flood, the K/Na ratio reaches its maximum values (up to 0.58). R. Ild is located in a zone of excessive moisture and is characterized by good soil leaching, especially from readily soluble salts (sulfates and chlorides), groundwater has extremely low concentrations of sulfates (less than 2 mg/dm3) and chlorides (2–4 mg/dm3). In 2009, the concentration of chlorides in the water of the studied water area does not exceed 8.0 mg/dm3 on average, in 2010 – 13.0 mg/dm3. In the place of mixing of river and reservoir waters, a decrease in the content of chlorides in water by dilution is observed. The concentration of sulfates in the water of the studied water area in 2009 averaged 3.6–13.3 mg/dm3, in 2010 – 3.6–22.9 mg/dm3. Due to the active biogenic absorption of sulfates, their minimum concentrations are inherent in the summer low-water period in both studied years. The content of hypothetical salts also shows that the amount of MgSO4 in June–July is less than in other periods.