Characteristics of the Community Structure and Driving Factors of Macrozoobenthos in the Fengxi River Basin of Poyang Lake

Macrozoobenthos play a key role in maintaining ecosystem stability and are often used as bioindicator of water pollution and eutrophication. This study conducted a field survey in the upper reaches of the Fengxi River in June 2023 to investigate the community characteristics of macroinvertebrates and its influencing factors, based on measurements of water physicochemical properties. The survey results show that a total of 24 species of macrozoobenthos were collected, belonging to 2 phyla, 4 classes, 8 orders and 14 families, including 9 species of Arthropoda and 15 species of Mollusca. The biomass of Mollusca was significantly higher than that of Arthropoda (P< 0.05). Significant spatial differences were observed in the community structure (P<0.05), with species richness and abundance at sampling points Y1-Y5 being lower than those at Y7-Y9. The abundance of each sampling point ranged from 0 to 1 018 ind·m^-2, and the biomass ranged from 0 to 751.04 g·m^-2. The dominant species included Caridna nilotica gracilipes, Semisulcospira cancelata and Koreoleptoxis pacificans. Synchronously monitored water physicochemical parameters indicated that water temperature ranged from 20.6 to 27.5 ℃, pH from 7.46 to 8.68, total nitrogen concentration from 1.06 to 2.06 mg·L^-1, total phosphorus concentration from 0.03 to 0.10 mg·L^-1, and COD_Mn from 2.21 to 3.26 mg·L^-1. Diversity analysis show that the Margalef richness index had significant spatial variation, while the Pielou evenness index, Shannon-Wiener diversity index and Simpson diversity index had small fluctuations. Correlation analysis show that the biomass and abundance of macrozoobenthos were extreme significantly and positively correlated with nitrogen and phosphorus concentrations (P<0.01), while diversity indices was significantly and negatively correlated with pH value and water depth (P<0.01). RDA analysis further show that environmental factors explained 83.08% and 76.27% of the biomass and abundance, respectively, with total nitrogen, nitrate nitrogen, nitrite nitrogen, water depth, ORP and pH value being key environmental factors affecting the distribution of macrozoobenthos. This study clarifies the environmental driving mechanism of the community structure of macrozoobenthos in the Fengxi River, providing a scientific basis for watershed ecological protection and water quality monitoring.