Spatiotemporal Distribution Characteristics of Phytoplankton Communities in Baiyangdian Lake and Their Driving Factors
Phytoplankton are highly sensitive to environmental changes and respond rapidly, making their community dynamics crucial early warning indicators of lake ecosystem health. Previous studies have qualitatively analyzed the combined effects of multiple physicochemical water quality factors on phytoplankton communities, but few have quantitatively distinguished direct from indirect effects. This study employed correlation analysis, redundancy analysis, and structural equation modeling to investigate the spatiotemporal distribution of phytoplankton communities in Baiyangdian Lake and their driving factors. A total of 113 species belonging to 57 genera and 7 phyla were recorded. Phytoplankton density exhibited significant seasonal and spatial variability, peaking in summer. Diatoms and green algae dominated in spring, transitioning to cyanobacterial dominance in summer and autumn, and reverting to green algae in winter. Structural equation modeling revealed that water temperature had a total positive effect on phytoplankton biomass (β = 0.96), comprising a direct positive effect (β = 0.94, P < 0.05) and an indirect positive effect via increased abundance (β = 0.02). Total nitrogen (TN) had a negative total effect on biomass (β = -0.98), with a direct negative effect (β = -0.97, P < 0.05) and an indirect negative effect via reduced abundance (β = -0.01). TN also negatively affected abundance (β = -0.15, P < 0.05). These findings provide a scientific basis for ecosystem health assessment, eutrophication control, and biodiversity protection in Baiyangdian Lake.