Abstract: To explore the impact of the construction of cascade reservoir on water ecological environment in inland river, macrozoobenthos of the upper and middle reaches of Heihe River (reservoir area and natural river) were investigated from July to August in 2018. In terms of biodiversity index, dominance index and ABC comparative curve, the community and diversity of macrozoobenthos and its response relationship with human activities such as hydro-power cascade construction were analyzed. The results indicate that 43 species of macrozoobenthos were collected, of which 76.75% belong to arthropods, 18.60% belong to molluscs, and 4.65% belong to annelids, and significant spatial differences of the species number and diversity were found, with the values in natural river section significantly higher than those of the reservoir area. In addition, the reservoir area was dominated by static water species. ABC curve analysis show that the habitat in cascade reservoir area gradually became simplified due to the influence of cascade reservoir construction, with the species succession turned gradually from the river type to the static water type of the reservoir. The reaches of the river below the dam were influenced by the disturbance of tail water, where the species composition and diversity of macrozoobenthos showed a decreasing trend. In the middle natural river reaches, as the sewage produced by industry, agriculture and domestic life was directly or indirectly injected into the river, the pollution degree of the river was therefore aggravated, and the concentration of organic matter and nutrients increased significantly, the habitat heterogeneity were improved, the species composition was rich, showing the pollution-resistant dominant type. In addition, climate factors, such as altitude and water temperature were also the key factors affecting the distribution of macrozoobenthos community.

Key words: macrozoobenthos, community structure, species diversity, cascade reservoir, Heihe River