Microcystis bloom control using hydrogen peroxide and floatingsodium percarbonate algaecide Lake Guard Oxy in Florida

Abstract

Harmful algal blooms (HABs) pose a critical threat to aquatic ecosystems, human health, and economies globally, necessitating effectivemitigation strategies. This study investigated the efficacyof two hydrogen peroxide treatments, liquid hydrogen peroxide and sodium percarbonate algaecide Lake Guard Oxy (LGOxy), in the fieldduring a Microcystis bloom in the Caloosahatchee River, Florida, USA. Initial results indicated bloom suppression following both the liquid hydrogen peroxide and LGOxy treatments as 79% and 46% reduction in cyanobacterial relative abundance in 16S rRNA gene amplicon sequencing, 81% and 90% reduction in chlorophyll-a, and 91% and 97% reduction in Microcystis colony density. Both treatments were effectivein reducing cyanobacterial abundance in the short term, from immediately after application to the following day. However, their effectsdid not persist longer term (several days to a week), likely because water exchange occurred through the connection to a flowingsystem. LGOxy exhibited a more targeted impact on Microcystis than other cyanobacterial species, likely because Microcystis forms thin surface blooms that remain in contact with the buoyant LGOxy particles. We also observed increased upregulation of the expression of nitrogen fixationgenes in diazotrophs, such as Dolichospermum, based on transcriptomic analysis, particularly following LGOxy application. Ultimately, three treatments within 2 weeks (one liquid application and two LGOxy treatments) were not sufficientto fully eliminate the cHAB from the riverine study site after 14 days. This underscores the limitations of hydrogen peroxide-based treatments when target HABs are already established and the challenges facing deployment in open or actively flowinghydrologic systems.