Spatial and Seasonal Dynamics of Plankton Community and Its Relationship with Environmental Factors in an Urban River: A Case Study of Wuxi City, China

To explore how environmental factors affect the structure of plankton in urban rivers, we analyzed the Caowangjing River, an urban river that passes through Wuxi, to survey the water environmental factors and plankton population in different seasons. We identified 103 phytoplankton species belonging to eight phyla, with Chlorophyta, Bacillariophyta, and Cyanobacteria being the dominant groups. A total of 45 zooplankton species belonged to three classes, with Rotifera being the dominant class. Phytoplankton density was highest in the autumn, followed by the spring, and the lowest in the summer. Phytoplankton biomass, along with zooplankton density and biomass, exhibited seasonal declines. The average values of the Shannon–Wiener index, Pielou’s evenness index, and Margalef richness index were 3.58 ± 0.50, 0.72 ± 0.76, and 2.03 ± 0.31, respectively, indicating the Caowangjing River was mildly polluted based on a water quality evaluation. Redundancy analysis showed that turbidity, water temperature, and ammonia nitrogen are the key factors of phytoplankton community distribution, while water temperature, the permanganate index, and ammonia nitrogen are the key factors of zooplankton community distribution.