Phytoplankton assemblage characteristics and driving factors in Baiyangdian Lake under strong anthropogenic disturbance

Abstract

Despite being widely used as indicators of lake ecosystem health, the responses of phytoplankton assemblages to intensive anthropogenic disturbances remain poorly understood. Species identification, biodiversity assessment, Pearson correlation, redundancy analysis (RDA), and hierarchical clustering were integrated to disentangle the drivers structuring phytoplankton assemblages in Baiyangdian Lake under intensive anthropogenic disturbance. The results showed that 141 species of phytoplankton belonging to seven phyla were detected in Baiyangdian Lake. Bacillariophyta (35.5%) and Chlorophyta (33.57%) dominated the whole lake. The average Shannon–Wiener index (H) of the whole lake reached 2.77, and the average Margalef richness index (dM) was 4.19, indicating overall ecological recovery. Significant spatial heterogeneity existed across three dredging areas: the proportion of Bacillariophyta reached 51.9% in intensive dredging areas, much higher than 43.5% in light dredging areas and 38.7% in nondredging areas, whereas Chlorophyta exhibited an opposite distribution pattern. RDA results showed total nitrogen (TN), dissolved oxygen (DO), and permanganate chemical oxygen demand (COD_Mn) were core driving factors, jointly explaining 44.76% of total community variation. TN exerted dual threshold effects on phytoplankton diversity: moderate TN concentrations increase Shannon–Wiener diversity, whereas excessive TN levels reduce species richness. Low DO selectively stimulates the proliferation of diatoms, while COD_Mn boosts algal growth via carbon source provision. Ecological dredging reshaped sediment nutrient gradients and accelerated community succession toward diatom-green algae codominance. Short-term increases in turbidity suppressed algal density, while long-term reductions in internal nutrient release stabilized assemblage structure. This study quantifies combined effects of water quality and dredging on autumn phytoplankton (results are autumn-specific), providing new insights into algal succession across dredging gradients in disturbed northern shallow macrophyte lakes.