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Abstract
Superoxide (O2–) is a reactive oxygen species (ROS) that is primarily produced by the one-electron transfer of photo-oxidized colored dissolved organic matter (CDOM) in sunlit natural waters. Superoxide has dual oxidative and reducing properties to control the fate of oxygen and subsequent photochemically-mediated redox reactions. Here we examine the environmental and chemical parameters that control O2– photochemical decay pathways in natural water using the enzyme superoxide dismutase (SOD). Freshwater samples were used to establish a reproducible natural photochemical source material and then augmented chemically to mimic specific seawater constituents (ionic strength, buffer, halides, and pH). SOD was used to compare redox pathways and infer maximal O2– photoproduction rates from H2O2 measurements quantified by flow injection chemiluminescent analysis. These results will help illuminate the parameters that control O2– pathways in irradiated samples and deepen our understanding of the role of photochemistry in biogeochemical cycles and the redox state of sunlit waters.