Phytoplankton Community Structure and Its Response to Environmental Factors in the Cascade Hydropower Stations of the Lower Jinsha River

Background The construction of cascade hydropower stations on the lower Jinsha River has significantly altered hydrological conditions and ecological processes. Understanding how phytoplankton communities respond to these changes is essential for reservoir management and ecosystem conservation. This study examines the vertical and seasonal dynamics of phytoplankton and their relationships with key environmental factors in four cascading reservoirs. Results Significant seasonal stratification of water temperature, dissolved oxygen, turbidity, and total dissolved solids was observed in June but not in December. Phytoplankton community structure varied markedly with depth and season. Cyanobacterial density increased from June to December, while diatoms and green algae decreased. Mantel tests revealed that temperature, dissolved oxygen, and nitrate nitrogen were positively correlated with phytoplankton abundance and biomass in both seasons. Nutrients such as TN and TP also influenced community structure, particularly in deeper layers. Conclusion The findings demonstrate that thermal stratification, nutrient availability, and seasonal changes jointly regulate phytoplankton dynamics in subtropical cascade reservoirs. These insights are critical for guiding water quality management and ecological protection strategies in regulated river systems.