水文季节驱动下梯级开发河流浮游植物群落构建机制的转换OA

Cascaded hydropower dams fragment river connectivity and alter aquatic ecosystem structure,consequently threatening the health and stability of river ecosystems.As primary producers,phytoplank-ton are excellent indicators of river health and dynamics.Therefore,understanding the structural charac-teristics and community assembly mechanisms of the phytoplankton community is essential for providing data critical for supporting river conservation and management.In this study,a river reach with cascaded hydropower stations in the Jinjiang River basin was selected for case study and we analyzed the phyto-plankton community structure in different seasons and the influence of varying hydrological regimes on community assembly mechanisms in the context of cascaded dams.In October(wet season)of 2024 and March(dry season)of 2025,simultaneous monitoring of phytoplankton and water environmental factors was carried out at 11 monitoring sites in the Xixi reach of Jinjiang River basin.The relative contributions of deterministic and stochastic processes in community assembly were then quantified using a combina-tion of the neutral community model(NCM),modified stochasticity ratio(MST)and hierarchical parti-tioning,and key driving environmental factors were identified.Results show that:(1)During the wet sea-son,the average phytoplankton density was 0.4×107 cells/L,with dominance by Cyanobacteria,Chlo-rophyta,and Bacillariophyta.Phytoplankton density increased from upstream to downstream,peaking at the Jinjizha(JJ)hydropower station site,where Cyanobacteria accounted for 64.77%of the total abun-dance.During the dry season,phytoplankton densities varied significantly among sites,with the lowest density at Xinlan(XL)hydropower station site and the highest at the Anxi Chengxi bridge sluice(CX).(2)Deterministic processes played a more significant role in the community assembly during the wet sea-son(NCM fit R²=0.313,MST<0.5),whereas stochastic processes were more influential during the dry season(R²=0.578,MST>0.5).(3)Hierarchical partitioning analysis indicated that flow velocity was the most influential environmental factor in the wet season(explaining 18.28%of the variation),while total phosphorus(TP,11.47%)and the permanganate index(CODMn,10.25%)were the primary drivers in the dry season.The findings of this study provide a scientific basis for ecological operation of cascaded reser-voirs and water quality management in the rivers of Jinjiang River basin.