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On the basis of the “Environmental quality standard for surface water” (GB 3838-2002) in China, eight water quality indexes were measured in M River, including pH, water temperature (T), transparency (SD), dissolved oxygen (DO), chemical needs Oxygen (COD), ammonia nitrogen (NH3-N), total nitrogen (TN), total phosphorus (TP). Using the single factor index method, it is concluded that the water pollution of M River is serious and the water quality is beyond Grade V of water environment standard. Moreover some indexes of the water quality meet with the standard level, including COD, NH3-N, TN and TP. The Pearson correlation analysis is conducted between water quality indexes and phytoplankton community parameters. After phytoplankton qualitative and quantitative analysis, the phytoplankton community characteristics in Minxin River were analyzed by Dominance index (Y), Shannon-Wiener diversity index (H’), Margalef Species diversity index (d) and Pielou evenness index (J). H’ and TN was a significant positive correlation (r = 0.923, P

An investigation of phytoplankton community and water quality for M River was conducted in December 2019.The results showed that 38 species of phytoplankton belonging to 6 phyla and 26 genera were collected. Among them, Bacillariophyta is the richest species, which accounted for 34.21%, followed by Cyanophyta with 26.32% and Chlorophyta with 28.95%. The density of phytoplankton was 63.0*106 inds/L which indicated as eutrophic water body. The highest density was Bacillariophyta, accounting for 51.03%. The Shannon-Wiener diversity index (H’) varied from 1.34 to 2.24, the Margalef Species diversity index (d) varied from 2.71 to 3.85, and the Pielou evenness index (J) varied from 0.38 to 0.67. According to the integrative analysis results of H’, d and J, M River water quality belongs to oligo-polluted, but individual sites belong to meso-polluted.