Hydrobiological studies in the area of Sokolov oil fields

The article presents the indicators of biological diversity and productivity of zooplankton communities and zoo-benthos of the Kizan River in the area of the object of accumulated environmental impact of the Sokolovsky oil pits (the Volga River delta, Astrakhan Region, the vicinity of the village of Kizan). It was revealed that the dominant groups of organisms in the study area are Calanoida, Cyclopoida. Each of the studied stations is distinguished by dominant species – Calanus helgolandicus at station 1, Cyclops sp. at station 2, Daphnia ambigua and Polyphemus pediculus at station 3 were predominant in number. The positive impact of coastal reclamation on the biomass and composition of zooplankton is shown. The number of zooplankton at the station where restoration work was previously carried out was maximum – 32.5 thousand specimens/m3. The biomass in this area also exceeded the values at other stations by more than two times and amounted to 3.8 g/m3. The study of the species composition of zooplankton allowed us to estimate the degree of saprobity of the studied section of the Kizan River. The saprobity analysis revealed zones of moderate (β-mesosaprobic) and strong (α-mesosaprobic) pollution with organic substances. Eight species of organisms were registered in the macrozoo-benthos; crustaceans were the dominant group of the benthocenosis near the shore. A significant share in the sample was also occupied by the larvae of dipterous insects Chironomus plumosus and Cricotopus sylvestris. Mollusks Viviparus viviparus and Lymnaea stagnalis were found as single specimens. At a distance of several meters from the coastline, an increase in the number of zoobenthic organisms in the sample up to 60 specimens/m2 was noted. The dominant species remain amphipods, making up 33.3% of the total number of individuals and represented by two species (Gammarus minutus and Dikerogammarus villosus). A significant number of dipteran larvae (Culex pipiens and Cricotopus sylvestris) were found, making up 31.7% of the total number of organisms.