Community Structure and Toxin-Producing Traits of Bloom-Forming Algae in the Danjiangkou Reservoir

This study investigated the community structure and toxin-producing characteristics of bloom-forming algae in the Danjiangkou Reservoir to provide a scientific basis for bloom risk management. From July to September 2025, surface water samples were collected from 15 sites across the reservoir. Algal composition was determined by microscopic cell counting, while concentrations of microcystins and cylindrospermopsins and the proportion of toxin-producing strains were measured using ELISA, quantitative PCR, and mass spectrometry. Cyanobacteria dominated the phytoplankton community, accounting for over 80% of total abundance, with dominant species including Dolichospermum, Pseudanabaena, Aphanocapsa, Leptolyngbya, and Microcystis. Spatially, Dolichospermum and Pseudanabaena were prevalent in reservoir bays and tributary inflows, whereas the main reservoir and downstream areas were dominated by simpler communities, primarily Dolichospermum or Aphanocapsa. Toxin analysis revealed low levels of cylindrospermopsin only at the Madeng site, with a minimal proportion of toxin-producing strains (0.3%–1.7%), and microcystin concentrations remained low overall. These results indicate that the Danjiangkou Reservoir is currently in a high-biomass, low-diversity cyanobacterial state, with a generally low risk of toxin production.