[Variation Characteristics and Driving Factors of Phytoplankton Community in the Sediment-laden Rivers of the Jinghe River Basin].

In order to explore the characteristics of phytoplankton communities in the sediment-laden rivers of the Jinghe River Basin and their response to changes in environmental factors， this study systematically investigated the main stream and eight typical tributaries of the Jinghe River Basin in November 2021 （autumn） and May 2022 （spring）. A total of 209 species of phytoplankton were identified in seven phyla and 72 genera， with that in autumn of 2021 （126 species） being lower than that in spring of 2022 （179 species）. Bacillariophyta and Chlorophyta were the dominant phyla of phytoplankton in the two seasons. In the autumn of 2021， the average density and biomass of phytoplankton were 89.21×10⁴ cells·L^-1 and 1.48 mg·L^-1， while in the spring of 2022， the average density and biomass of phytoplankton were 265.92×10⁴ cells·L^-1 and 4.80 mg·L^-1. The Shannon-Wiener diversity index and Margalef richness index of phytoplankton in spring 2022 were higher than those in autumn 2021， while the Pielou evenness index had no significant seasonal difference. The results of correlation analysis showed that nitrogen and phosphorus nutrients， chemical oxygen demand， dissolved oxygen， and turbidity were the main environmental factors affecting the density of dominant species of phytoplankton in the two seasons， and the density of most dominant species was significantly negatively correlated with turbidity. The results of variation decomposition and the structural equation model showed that the physical and chemical parameters of the water body had a greater relative contribution to the phytoplankton density and Chl-a concentration in the two seasons. The land use （mainly forest land and cultivated land） in the 1 000 m riparian buffer zone indirectly affected the phytoplankton density and Chl-a concentration in the two seasons by acting on the total nitrogen， total phosphorus， nitrite nitrogen， chemical oxygen demand， and turbidity in the physical and chemical parameters of the water body， and the physical factor （turbidity） had a significant effect on the phytoplankton density and Chl-a concentration in the two seasons.