Донная фауна и оценка экологического состояния нижнего участка р. Ангары

Abstract

On the Angara River there is a reservoirs cascade of four hydroelectric power stations, and in the lower reaches it is planned to build the Nizhneboguchanskaya HPS. On the other hand, at present there is a significant gap in the studies of the Angara lower section, especially in zoobenthos. The material for the study was zoobenthos samples taken in the coastal zone in August 2022 at 11 river stations in a section from 445 km to 9 km from the mouth. Biotopes of zoobenthos are represented mainly by pebble-sandy soil with varying degrees of silting. The benthic fauna of the Angara River was gammarid-chironomid in nature; oligochaetes were found everywhere, but in small numbers. 87 species and taxa of a higher rank had been identified, the largest number of species (37) was noted among the chironomid larvae of Orthocladiinae and Chironominae. The quantitative advantage (more than 60% of the abundance and biomass) belonged to amphipods. Chironomids predominated over amphipods only on silty bottoms; in the river section, in general, they accounted for 24% of the abundance and 10% of the biomass of benthic communities. The Shannon species diversity index was relatively low and amounted to 2.3 bit/ind. general in the section. The lower reaches of the river were characterized by the highest species diversity, but the lowest number of benthic invertebrates. The total number of zoobenthos in the studied area was 2,9 thousand ind/m2, biomass – 14,6 g/m2, in the lower reaches of the river the number decreased to 1.7 thousand ind/m2, biomass – up to 4 g/m2. An integrated approach was used to assess the water quality of the Angara benthic communities, that includes the analysis of 8 bioindication indices: Goodnight (G), Woodiwiss (TBI) and saprobity (S) indices (recommended by the Russian regulatory document); indices FBI, BMWP, ASPT (recommended by the European Water Framework Directive); the Balushkina chironomid index (K) and the Shannon species diversity index. The fundamental criterion for the selection of indices was the level of development of indicator taxa. The complex assessment revealed the trend of improving water quality to the mouth of the river. This trend is expressed in the consistent dynamics of the TBI, BMWP, ASPT indices, which can be recommended for assessing the ecological state of the Angara River and other watercourses in the region. The water quality corresponded to Class III (Polluted) with a tendency to improve at the mouth to Class II (Slightly polluted).