| Summary: | Total S concentration in the top 35 cm of Big Run Bog peat averaged 9.7 u molg-wet mass -1 (123 u molg dry mass -1 ). Of that total, an average of 80.8% was carbon bonded S, 10.4% was ester sulfate S, 4.5% was FeS 2 -S, 2.7% was FeS-S, 1.2% was elemental S, and 0.4% was SO 4 2- -S. In peat collected in March 1986, injected with 35 S-SO 4 2- and incubated at 4 degreesC, mean rates of dissimilatory sulfate reduction (formation of H 2 S + S 0 + FeS + FeS 2 ), carbon bonded S formation, and ester sulfate S formation averaged 3.22, 0.53, and 0.36 nmolg wet mass -1h -1 , respectively. Measured rates of sulfide oxidation were comparable to rates of sulfate reduction. Although dissolved SO 4 2- concentrations in Big Run Bog interstitial water (< 200 uM) 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 mmolm -2d -1 (at 4 degreesC) 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 SO 4 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.
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