Seasonal Variation and Driving Factors of Metazooplankton Community in the Cascade Reservoirs

To investigate the structural characteristics and driving factors of the metazooplankton community in the cascade reservoirs of Feiyun River Basin, monitoring surveys were conducted at 18 sampling sites across different seasons: September 2021 (autumn), January 2022 (winter), May 2022 (spring), and July 2022 (summer). These surveys identified 51 metazooplankton species, with the highest species abundance observed in summer and the lowest in winter. Notably, metazooplankton densities and biomasses peaked in spring, averaging 13.57 ind./l (where ind./l stands for individuals per liter) and 0.362 mg/l, respectively, while the lowest average densities (9.20 ind./l) and biomasses (0.262 mg/l) occurred in summer and winter, respectively. Seasonal variation had a notable influence on the community composition of metazooplankton, with Rotifera predominating in summer and autumn, and Copepoda in winter and spring. Cyclops larva and Nauplius species consistently dominated throughout. Correlation analyses revealed a significant negative association between metazooplankton richness and Pielou evenness indices with phosphate and total phosphorus concentrations, respectively. Redundancy analyses identified chlorophyll a, water temperature, total phosphorus, conductivity, pH, and phosphate as key environmental factors influencing the seasonal distribution of the metazooplankton community. This study provides a preliminary assessment of the seasonal dynamics of metazooplankton communities in the cascade reservoirs of the Feiyun River Basin, offering foundational insights for evaluating the ecological health of the basin waters.