Macrozoobenthos of the Lower Reaches of the Ustye River

In 2021-2022, the main characteristics of macrozoobenthos were studied and the water quality in the lower reaches of the Ustye River (Yaroslavl oblast) was assessed. A total of 105 lower defined taxa were recorded in the macrozoobenthos, the main representatives of which were chironomid larvae (37) and mollusks (14). For the first time, larvae of the chironomid Saetheria c.f. tylus were recorded for the benthic fauna of the Yaroslavl oblast. The maximum species richness was noted in autumn in ripal', due to the mass appearance of amphibiotic insect larvae. The dominant species for all types of soils were Tubifex newaensis and Unio pictorum. The maximum abundance was observed in ripal' in spring, in medial in summer and autumn. The basis of the abundance of macrozoobenthos on all types of soils was formed by chironomids, and the biomass was formed by oligochaetes. The dynamics of abundance and biomass observed during the study period is mainly due to the peculiarities of the life cycles of chironomids and other amphibiotic insects. When assessing water quality based on macrozoobenthos indicators, a gradual improvement in conditions from May to October was shown, the transition from quality class III to II, which indicates a high potential for self-purification of the reservoir.