Role of Sulfate Reduction Versus Methanogenesis in Terminal Carbon Flow in Polluted Intertidal Sediment of Waimea Inlet, Nelson, New Zealand

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Abstract
An investigation of the terminal anaerobic processes occurring in polluted intertidal sediments indicated that terminal carbon flow was mainly mediated by sulfate-reducing organisms in sediments with high sulfate concentrations (>10 mM in the interstitial water) exposed to low loadings of nutrient (equivalent to 2 kg of N · day −1 ) and biochemical oxygen demand (10 2 kg of N · day −1 ) and biochemical oxygen demand (>0.7 × 10 3 kg · day −1 ), methanogenesis was the major process in the mediation of terminal carbon flow, and sulfate concentrations were low (≤2 mM). The respiratory index [ 14 CO 2 /( 14 CO 2 + 14 CH 4 )] for [2- 14 C]acetate catabolism, a measure of terminal carbon flow, was ≥0.96 for sediment with high sulfate, but in sediments with sulfate as little as 10 μM in the interstitial water, respiratory index values of ≤0.22 were obtained. In the latter sediment, methane production rates as high as 3 μmol · g −1 (dry weight) · h −1 were obtained, and there was a potential for active sulfate reduction.