Resilience of microbial communities after hydrogen peroxide treatment of a eutrophic lake to suppress harmful cyanobacterial blooms. H2O2 lake treatment

Applying low concentrations of hydrogen peroxide (H2O2) to lakes is an emerging method to mitigate harmful cyanobacterial blooms. While cyanobacteria are very sensitive to H2O2, little is known about the impacts of these H2O2 treatments on other members of the microbial community. In this study, we investigated changes in microbial community composition during two lake treatments with low H2O2 concentrations (target: 2.5 mg L-1) and in two series of controlled lake incubations. The results show that the H2O2 treatments effectively suppressed the dominant cya-nobacteria Aphanizomenon klebahnii, Dolichospermum sp. and to a lesser extent Planktothrix agardhii. Microbial community analysis revealed that the relative abundances of many bacteria were not significantly affected by the H2O2 treatments, several Proteobacteria profited from the treatments (e.g., Alteromonadales, Pseudomonadales, Rhodobacterales), and some bacterial taxa de-clined (e.g., Verrucomicrobia). Alpha- and beta-diversity showed a temporary decline but recov-ered within a few days, demonstrating resilience of the microbial community. The predicted functionality of the microbial community revealed a temporary increase of anti-ROS defenses and glycoside hydrolases but otherwise remained stable throughout the treatments. We conclude that the use of low concentrations of H2O2 to suppress cyanobacterial blooms is not detrimental to lake microbial communities and their ecosystem functioning.