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

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 <10 2 kg of N · day −1 ) and biochemical oxygen demand (<0.7 × 10 3 kg · day −1 ) in effluents from different pollution sources. However, in sediments exposed to high loadings of nutrient (>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.