Abstract: To understand the community structure of benthos and its relationship with environmental factors in Ulungur Lake, six surveys were conducted on benthos and environmental factors at 28 sampling sites in five sites of Ulungur Lake from 2019 to 2021. A total of 68 species of benthos belonging to 4 phyla, 14 orders and 21 families were collected. Chironomus larvae and oligochaetes dominated the community, while Chironomus salinarius, Chironomus sp. and Procladius sp. were the dominant species throughout the year. There were significant temporal and spatial variations of environmental factors (P<0.05). The density and biomass of benthos exhibited variations across both time and space. The average density and biomass of benthos in spring, summer, and autumn were 851, 529, 669 and·m^-2 and 19.52, 14.60, and 13.39 g·m^-2, respectively. The density and biomass in spring were mainly concentrated in the middle of the Buluntuohai Lake (987 ind·m^-2, 24.29 g·m^-2) and the south of Jili Lake (1040 ind·m^-2, 21.32 g·m^-2). Summer density and biomass mainly concentrated in Luotuobozi Lake (896 ind·m^-2, 30.12 g·m^-2). Autumn density was mainly concentrated in the southern part of Jili Lake (808 ind·m^-2) and Luotuobozi Lake (864 ind·m^-2). The biomass in autumn was concentrated in the southern part of Jili Lake (16.07 g·m^-2) and Luotuobozi Lake (14.81 g·m^-2), as well as in the 73 km Xiaohaizi Lake (15.74 g·m^-2). Principal component analysis and similarity analysis showed that the benthos community structure had significant spatiotemporal variations (P<0.01). The significant indicator species differed in different lakes. Redundancy analysis showed that salinity, total nitrogen, and electrical conductivity were important factors affecting the community structure of benthos across different seasons. These factors exhibited significant positive correlations with oligochaetes and chironomid larvae, while significant negative correlation with most benthos. Water salinity, nutrients, and organic pollutants were the main threats to the ecological environment of Ulungur Lake. Both climate change and human activities have exerted considerable stress on the structure of benthos community.

Key words: macrobenthos, community structure, species indicator value, environmental factor, Ulungur Lake