Complex effects of dissolved organic matter, temperature, and initial bloom density on the efficacy of hydrogen peroxide to control cyanobacteria

Abstract

Harmful cyanobacterial blooms plague reservoirs and lakes used for a variety of purposes. Chemical controls are frequently used to mitigate the occurrence of cyanobacterial blooms given that many are fast-acting and effective at reducing cyanobacterial abundance. Recent research has identified hydrogen peroxide (H2O2) as an environmentally-friendly alternative to algaecides that have typically been used, such as copper sulfate. To build on past studies, these experiments sought to further understand how well H2O2 treatments reduce cyanobacteria in complex eutrophic conditions. We assessed the effectiveness of H2O2 (at treatments of 2-16 mg L-1) under varying environmental conditions in a controlled laboratory setting, including (1) dissolved organic matter (DOM) concentrations (humic acid; 0 - 60 mg L-1), (2) temperatures (20, 25, and 32 °C), and (3) initial algal biomass (82 – 371 µg L-1 as chlorophyll). In contrast to our expectations, neither DOM concentration nor temperature meaningfully impacted the effectiveness of H2O2 at reducing cyanobacteria. However, initial algal biomass as well as H2O2 treatment greatly influenced the effectiveness of the algaecide. Across all experiments, H2O2 concentrations of 0.03 - 0.12 mg H2O2 L-1/µg chlorophyll L-1 were effective at significantly reducing cyanobacteria. Thus, water resource managers are encouraged to consider how ambient levels of algal biomass may affect the ability of H2O2 to control algal blooms prior to treatment.