Oxidation and incorporation of hydrogen sulfide by dissolved organic matter

Redox reactions of sulfide with dissolved organic matter (DOM) are potentially important for sulfur cycling in anoxic environments. We investigated the chemical oxidation of H2S with a peat humic acid in batch experiments at pH 6, quantified the electron accepting capacity (EAC), and applied a first order kinetic model to estimate reaction constants. Dissolved ferric iron was used to quantify electron donating capacities (EDC). Hydrogen sulfide was oxidized to thiosulfate and also incorporated into DOM. Fourier-transformed infrared (FTIR) spectroscopy suggested formation of aryl polysulfide. Electron transfer was significantly correlated to DOM concentration and amounted to 0.60 (EAC) and 0.63 (EDC) meq g− 1 C. DOM concentrations > 60 mg l− 1 lead to decreased capacities per unit mass carbon. The overall reaction of sulfide with DOM could be adequately described by a kinetic model comprising a redox-active and an S-incorporating DOM pool. The overall reaction was fast, with H2S half-lives on the order of several hours. The results suggest that DOM may chemically reoxidize H2S in organic rich soils and sediments at significant rates.