Cycling of inorganic and organic sulfur in peat from Big Run Bog, West Virginia

Abstract

Total S concentration in the top 35 cm of Big Run Bog peat averaged 9.7 μmol·g — wet mass−1 (123 μmol·g dry mass−1). Of that total, an average of 80.8% was carbon bonded S, 10.4% was ester sulfate S, 4.5% was FeS2­S, 2.7% was FeS­S, 1.2% was elemental S, and 0.4% was SO4 2−­S. In peat collected in March 1986, injected with35S­SO4 2− and incubated at 4 °C, mean rates of dissimilatory sulfate reduction (formation of H2S + S0 + FeS + FeS2), carbon bonded S formation, and ester sulfate S formation averaged 3.22, 0.53, and 0.36 nmol·g wet mass−1·h−1, respectively. Measured rates of sulfide oxidation were comparable to rates of sulfate reduction. Although dissolved SO4 2− concentrations in Big Run Bog interstitial water (< 200 µM) are low enough to theoretically limit sulfate reducing bacteria, rates of sulfate reduction integrated throughout the top 30–35 cm of peat of 9 and 34 mmol·m−2·d−1 (at 4 °C are greater than or comparable to rates in coastal marine sediments. We suggest that sulfate reduction was supported by a rapid turnover of the dissolved SO4 2− pool (average turnover time of 1.1 days). Although over 90% of the total S in Big Run Bog peat was organic S, cycling of S was dominated by fluxes through the inorganic S pools.