Research on the changes in the Phytoplankton community and Cyanobacterial toxin content in Hoa Binh reservoir

Abstract

This study investigates the dynamics of the Phytoplankton community and the occurrence of Microcystin toxins in Hoa Binh reservoir from June 2023 to May 2024. A total of 44 Phytoplankton genera were identified, belonging to five phyla: Chlorophyta (50 %), Bacillariophyta (26 %), Cyanophyta (17 %), Dinophyta (5 %), and Euglenophyta (2 %). Among them, Chlorophyta and Dinophyta exhibited seasonal dominance, with Dinophyta thriving during the rainy season, while Chlorophyta prevailed in the dry season. Cyanobacteria exhibited low biomass, with four genera (Microcystis, Oscillatoria, Anabaena, and Pseudanabaena) identified as potential Microcystin producers, among which Microcystis accounted for 87.6 % of the total Cyanobacterial biomass. Microcystin concentrations ranged from 0.11 to 0.86 µg/L, below the WHO safety guideline of 1 µg/L, but still indicating a potential risk for domestic water use. Principal Component Analysis (PCA) and Pearson correlation analysis revealed no significant relationship between Microcystis biomass and Microcystin concentrations, suggesting the possible presence of non-toxic Microcystis strains or contributions from other Microcystin-producing taxa. Environmental factors, such as high pH, warm water temperatures, and high turbidity, were found to support the growth of Cyanobacteria, particularly Microcystis. No clear correlation was observed between Microcystis biomass or Microcystin concentrations and nutrient variables (nitrogen and phosphorus). These findings offer crucial insights into Phytoplankton succession and Microcystin-related risks in Hoa Binh reservoir, thereby informing water quality monitoring and management strategies.