Variations of zooplankton community as bioindicators of eutrophication and water quality in shallow Yangtze Lakes

The Yangtze River and its adjacent lakes form a complex river-lake ecosystem, rich in aquatic biodiversity, with zooplankton serving as a key component. Zooplankton is important in nutrient circulation and energy flow, and also serves as an important indicator reflecting water quality and the overall health of aquatic ecosystems. Studying the changes in zooplankton community structure, which fluctuate with physicochemical environment, is crucial for understanding variations in lake water quality. We surveyed 15 shallow lakes of this river-lake ecosystem in the middle reaches of the Yangtze River. Using K-means cluster analysis based on the relative density ratios of Protozoa, Rotifera, Cladocera, and Copepoda, we classified the lakes into three distinct groups (Groups I to III). Our results showed a decline in the density and biomass proportions of Cladocera and Copepoda, contrasted by increases in those of Protozoa and Rotifera from Group I to III, alongside a rise in the Trophic Level Index, indicating progressive eutrophication. A composite diversity index, derived from the diversity indices of Shannon-Weiner, Pielou, and Margalef by using Principal Component Analysis, revealed an increase in diversity from Group I to III, suggesting a gradual stabilization of the community structure. Redundancy Analysis identified water temperature (WT), chlorophyll-a (Chl-a), secchi depth (SD), orthophosphates (PO₄^3-), and dissolved oxygen (DO) as the primary environmental factors influencing zooplankton community structure. This study provides critical insights into the dynamics and environmental drivers of zooplankton community in these 15 lakes, offering a foundation for managing water eutrophication and facilitating the restoration of these aquatic ecosystems.