| Abstract
| - Hydrogen peroxide (H2O2), iron, and sulfide ion weremeasured every 4 h over 40-h periods at four hot springsin Yellowstone National Park, WY: an alkaline spring(Black Sand Pool); the sulfur-rich, near-neutral RoadsideSpring near Nymph Lake; and two iron-rich, acidic springs(Chocolate Pots and the iron-rich Roadside Spring nearNymph Lake). Hydrogen peroxide concentrations reached200−600 nM by late afternoon and decreased, in mostcases, to less than 50 nM during the night. Diel changesin H2O2 concentrations suggest that photochemically mediatedprocesses were responsible for its formation. Photochemicalreactions with DOC are likely the primary pathwayresponsible for H2O2 formation in geothermal waters.Although microbially mediated processes are important inlimiting the buildup of H2O2, the inverse relationshipbetween H2O2 and sulfide ion suggests that H2O2 decaymay also occur via chemically mediated processes in thesulfur-rich waters.
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