Assessment of the state of reservoirs of the Volga-Akhtuba interfluve Re-gional significance natural park by hydrochemical indicators

The article is devoted to assessing the state of reservoirs of various types of the Volga-Akhtuba Interfluve Nature Park, located in the Astrakhan region, according to hydrochemical indicators. The purpose of the study was to determine the level of pollution of water bodies by calculating the chemical pollution index CJ using the Bavarian approach. The study was conducted in July 2019 at 10 stations: 7 lakes, 1 erik and 2 rivers (Akhtuba and Volga). Hydrochemical parameters such as water temperature, hydrogen index pH, mineralization, electrical conductivity, nitrate ion content, ammonium cation, phosphate ion, dissolved oxygen and biochemical oxygen consumption BPK5 were selected as priority indicators. The results showed that the studied reservoirs had temperatures in the range from 21.2 to 25.1 °C, were predominantly slightly alkaline (pH 7.5-8.5), individual reservoirs (Lakes Carp, Curly) had elevated pH values exceeding the norms for fishery purposes. Water mineralization varies from 166 to 303 mg/l, which allowed the reservoirs to be classified as α-hypohaline freshwater. The electrical conductivity ranges from 259.38 to 473.44 µcm/cm. The level of dissolved oxygen (% saturation) in most reservoirs had normal values, while in terms of BPK5, the studied objects exceeded the maximum permissible concentration (2.1 mgO2/l) by 1.4–2.0 times. Biogenic elements represented by nitrate ammonium ions and phosphate were in the normal range. The calculated CJ index demonstrated a significant differentiation of the conditions of reservoirs: most belong to the second class of quality (“risk”), individual reservoirs (lakes Carp and erik Ulyankin) belong to the third class (“crisis”).