Controls on the photochemical production of hydrogen peroxide in Lake Erie

In Lake Erie, toxin-forming harmful algal blooms (HABs) occur following high concentrations of hydrogen peroxide (H2O2). Correlation between H2O2 concentrations and HABs revealed knowledge gaps on the controls of H2O2 production in Lake Erie. One way H2O2 is produced is upon absorption of sunlight by the chromophoric fraction of dissolved organic matter (CDOM). Rates of this photochemical production of H2O2 may increase in proportion to the apparent quantum yield of H2O2 (phiH2O2,lambda) from CDOM. However, the phiH2O2,lambda for H2O2 production from CDOM remains too poorly constrained to predict the magnitude and range of photochemically produced H2O2, particularly in freshwaters like Lake Erie. To address this knowledge gap, the phiH2O2,lambda was measured approximately biweekly from June-September 2019 in the western basin of Lake Erie along with supporting analyses (e.g., CDOM concentration and composition). The average phiH2O2,lambda in Lake Erie was within previously reported ranges. However, the phiH2O2,lambda varied 5-fold in space and time. The highest phiH2O2,lambda was observed in the Maumee River, a tributary of Lake Erie. In nearshore waters of Lake Erie, the phiH2O2,lambda decreased about five-fold from June through September. Integration of the controls of photochemical production of H2O2 in Lake Erie show that the variability in rates of photochemical H2O2 production was predominantly due to the phiH2O2,lambda. In offshore waters, CDOM concentration also strongly influenced photochemical H2O2 production. Together, the results confirm prior work suggesting that photochemical production of H2O2 contributes but likely cannot account for all the H2O2 associated with HABs in Lake Erie.

Automated summary

In Lake Erie, the occurrence of harmful algal blooms (HABs) is related to high concentrations of hydrogen peroxide (H2O2). The production of H2O2 in Lake Erie is influenced by the chromophoric fraction of dissolved organic matter (CDOM) through photochemical reactions. However, the exact controls of H2O2 production from CDOM remain unclear. By measuring phiH2O2,lambda and CDOM concentration in Lake Erie, this study found that the variability in rates of photochemical H2O2 production is predominantly influenced by phiH2O2,lambda and CDOM concentration. However, there are still other unknown factors controlling H2O2 production in Lake Erie.