March 2024 eNewsletter

Do Hydrogen Peroxide Concentrations in Lake Erie Influence the Toxicity of Microcystis Blooms?

Emma Johnson aboard the R/V Laurentian deploying a radiometer system to measure light in the water column.

Lake Erie provides drinking water for approximately eleven million people. During the summer months, Lake Erie has been plagued with cyanobacterial harmful algal blooms (cHABs) that can produce harmful toxins, threatening human health and aquatic life. The cHABs in Lake Erie are often composed of cyanobacteria of the genus Microcystis, which produces the toxin microcystin. Current thinking is that Microcystis makes this toxin to mitigate damage from hydrogen peroxide, an oxidative stressor present in high concentrations in Lake Erie.

Emma Johnson, a 2023-24 CIGLR Graduate Research Fellow and PhD student at the University of Michigan, is working with her advisor, Rose Cory, PhD (University of Michigan) and Casey Godwin, PhD (CIGLR) to gain a comprehensive understanding of Lake Erie Microcystis in relation to hydrogen peroxide concentrations. “Hydrogen peroxide is produced naturally in fresh and marine waters, at concentrations many orders of magnitude lower than in home medicine cabinets where it is used for its antimicrobial properties,” said Johnson. “Concentrations of hydrogen peroxide are higher in Lake Erie compared to other freshwaters due to abundant light and high amounts of dissolved organic matter, which fuel the production of hydrogen peroxide. On average, summertime concentrations of the toxin microcystin are positively correlated with summertime concentrations of hydrogen peroxide (Figure 1), suggesting that the toxin microcystin may protect Microcystis from oxidative stress caused by hydrogen peroxide, thereby contributing to the overgrowth of Microcystis in Lake Erie.”

Understanding why some summers have more or less toxic blooms in Lake Erie may depend on the processes that produce and destroy hydrogen peroxide in Lake Erie. “My work with CIGLR is providing me the opportunity to help tackle this challenge by utilizing ship resources for sampling and collecting data,” said Johnson.

During the 2023 summer cHAB, Johnson sampled the bottom and surface waters of western Lake Erie for any signs of hydrogen peroxide sources and sinks. She found that hydrogen peroxide concentrations were often higher in the bottom waters than in the surface waters (Figure 2).

Figure 1: Summertime average concentrations of particulate microcystin from 2014-2022 increase with increasing average concentrations of hydrogen peroxide. Each data point shows the summertime average ± standard error.

Figure 2: Concentrations of hydrogen peroxide (nM) in bottom vs. surface waters at western Lake Erie site WE12 during a week in mid-July 2023.













“This result is surprising because the well-known sources of hydrogen peroxide depend on sunlight and microbial biomass, which are more abundant in the surface than in the bottom water of Lake Erie,” said Johnson. “The water column was well-mixed during the study, and water column mixing should evenly distribute any hydrogen peroxide made in the surface waters. The higher concentrations of hydrogen peroxide in the bottom waters might suggest there is an unknown source of hydrogen peroxide in the sediments of Lake Erie.”

Johnson will use supporting water quality data to examine biogeochemical processes in the sediments. “Our team is focused on where potential net sources and sinks of hydrogen peroxide are located in Lake Erie’s western basin,” said Johnson. “cHABs are becoming more widespread, and it is imperative that we understand more about their environment and mechanisms for growth and toxicity.”