Low-concentration sodium percarbonate treatment of a severe cyanobacterial bloom: insights into chemical and biological changes in a small firewater reservoir.

Mitigating, controlling, and ideally preventing cyanobacterial blooms is an urgent priority because of their negative effects on aquatic (and indirectly terrestrial) ecosystems. Among algaecide-based approaches, hydrogen peroxide has proven effective at reducing cyanobacterial biomass, with the advantage of leaving no persistent residues in water or sediment. Although there is extensive research on hydrogen peroxide releasing sodium percarbonate as an oxidizing and disinfecting agent, the wide variety of environmental conditions, cyanobacterial species composition, and bloom dynamics make it necessary to conduct research on as diverse range of water bodies as possible. In this study, a severe cyanobacterial bloom in a firewater reservoir was treated with sodium percarbonate, followed by extensive monitoring of chemical and biological changes. Increases in conductivity and shifts in nitrogen forms showed that pre-treatment conditions strongly influence post-treatment water chemistry. Although short-term fluctuations in chemical parameters occurred, long-term patterns were driven mainly by environmental factors and biological activity. The results demonstrate that even in a severe bloom, cyanobacterial populations declined after treatment, but returned to pre-treatment levels within a week. The treatment did not reduce eukaryotic algal abundance; on the contrary, it led to a temporary increase in the abundance of green algae. Cyanobacterial peptide production was unaffected, indicating that reduced metabolite levels should not be necessarily assumed as a treatment outcome. Overall, the results further confirmed the effectiveness of sodium percarbonate towards cyanobacteria even during a severe bloom, while also highlighting that it is best suited for bloom prevention, taking into account pre-treatment phytoplankton composition and water chemistry.