Abstract: Understanding the seasonal variations of plankton community and the driving factors can provide basis for scientific protection of lakes. We examined the characteristics of phytoplankton community and its response to environmental changes in Hulun Lake with index method and correlation analysis method. The results showed that a total of 178 phytoplankton species belonging to 8 phyla were identified. The phytoplankton species composition was diatomic-green algae type, with Anabaena circinalis, Anabaena azotica, Cyclotella meneghiniana, and Microcystis wesenbergii as the dominant species. Seasonal variation of phytoplankton species followed a pattern of spring > summer > autumn. The average phytoplankton density and biomass was 810.140×10⁴ cells·L^-1 and 4.010 mg·L^-1, respectively. The density and biomass varied significantly across seasons. The average Shannon diversity index and Pielou evenness index of phytoplankton were 2.73 and 0.58, respectively, and both indices varied significantly among seasons. Based on the biodiversity index and comprehensive trophic level index (TLI), the water quality of Hulun Lake was at the level of mild eutrophication and the divers level is “good”. Redundancy analysis showed that total phosphorus, electrical conductivity, chemical oxygen demand, turbidity, chlorophyll a, and ammonium nitrogen were the main environmental factors affecting the distribution of phytoplankton community, and those influencing factors were different with seasons. Our results could provide a data reference for aquatic ecological restoration and water environmental protection in Hulun Lake.

Key words: phytoplankton, community structure, seasonal dynamics, water quality assessment, environmental factor, Hulun Lake