Abstract: The phytoplankton diversity of Daqinghe basin was analyzed in May and August in 2018. The results showed that there were a total of 58 species and 5 phyla in Daqinghe basin, indicating a high diversity of species. Among them, chlorophyceae were the main phytoplankton groups. There were 22 species of chlorophyte in the mainstream, accounting for 37.93% of the total phytoplankton species. The minority were chrysophyta accounting for 1.72%. Bacillariophyta had the maximum cell density of 6 004.33×10⁶ cell/L, accounting for 59.69% of the total cell density, while the chrysophyta were 3.76×10⁶ cell/L, accounting for 0.04%. The universal dominant species in the river were Microcystis aeruginosa, Synedra acus, Crucigenia quadrata, Scenedesmus dimorphus, Phormidium tenue, Stauroneis anceps and Schroederia spiralis. The cell density of phytoplankton hadunevenly spatial and temporal distribution. This paper used the Shannon-Wiener index, Pielou index and Margalef index to calculate the phytoplankton diversity of Daqinghe basin, indicating that the water quality in the Daqinghe basin was moderately polluted.

Key words: Daqinghe basin, phytoplankton, biodiversity