Emerging Contaminants Are Associated with Seasonal Variations in Phytoplankton Community Diversity in a Eutrophic Lake

Emerging contaminants (ECs) are increasingly detected in eutrophic lakes, yet their ecological contributions to phytoplankton community variation relative to conventional environmental factors remain poorly understood. Here, we investigated the spatiotemporal occurrence of typical ECs and associated phytoplankton community variation in Taihu Lake, China. Phytoplankton abundance was significantly correlated with water temperature and total phosphorus (P < 0.05). Among the EC groups, organochlorine pesticides (37.7%), per- and polyfluoroalkyl substances (16.7%), and polycyclic aromatic hydrocarbons (16.1%) showed strong associations with the spatiotemporal variation in phytoplankton community composition. Organochlorine pesticides explained 18.8% and 25.9% of the α-diversity variation in spring and summer, respectively, and interaction analyses suggested potential combined effects among contaminant groups. Water quality factors and ECs jointly explained 67.9% of the community variation, with stronger associations observed in summer than in spring. Higher dominance of Cryptomonas ovata in Gonghu Bay during spring and Microcystis sp. in Western Bay during summer was associated with reduced phytoplankton community diversity under combined gradients of eutrophication and ECs. These findings highlight the covariation of phytoplankton communities with eutrophication and ECs and provide new insights into ecological risk assessment and algal bloom management in shallow eutrophic lakes.