Abstract: To investigate the dynamic changes of cyanobacterial dominant species and their drivers before and after cyanobacterial blooms, a phytoplankton collection survey was conducted in a reservoir in southern China from January 2022 to April 2022. Three sampling sites were set up for water environment monitoring according to the characteristics of water diversion and supply of this reservoir. The principal coordinates analysis (PCoA) was used to explore and analyze the dissimilarity of dominant cyanobacterial species before and after the bloom, and the relationship between dominant cyanobacterial species and driving factors was analyzed by variation partitioning analysis (VPA) and linear fitting. Finally, reasonable prevention and control suggestions were provided for this reservoir. The results showed that three dominant species were identified before and after the cyanobacterial bloom, namely Pseudanabaena, Cylindrospermopsis raciborskii, and Raphidiopsis curvata, with a maximum density of 4.33×10⁷Cells/L. PCoA explained 86.41% of the difference between before and after the bloom. Pseudanabaena was dominant before the bloom (mixing period), and all three dominant cyanobacteria were rapidly reproducing and relatively balanced in proportion to the three during the bloom (stratification period). The VPA results showed that the driver of the area not directly affected by water diversion (point S3) explained more variations in the dominant cyanobacterial species (87.8%), and combined with the linear fit analysis, the most important driver of cyanobacterial blooms was the relative water column stability (RWCS), followed by water temperature (WT) and total phosphorus (TP). Based on the water regulation characteristics of high-loading nitrogen and phosphorus and the sudden spring
cyanobacterial bloom, thermal stratification can be eliminated to prevent and control the bloom effectively.