Effect of Different Electron Acceptors on Organic Carbon Mineralization and Transformation in a Freshwater Marsh.

Carbon mineralization in wetlands is limited due to the low availability of oxygen. Under such anoxic conditions, the presence of alternative electron acceptors such as NO₃^-, and SO₄^2- play a major role in the mineralization and transformation of organic carbon. Estimation of CH₄ and CO₂ production under different conditions is important for determining whether the wetlands serve as net C sinks or sources of atmospheric C. Kinetics of carbon gas emissions from a freshwater marsh soil treated with different levels of SO₄^2- and NO₃^- under anoxic conditions were monitored for 101 days. The total amount of CO₂ released did not show any significant difference among the treatments. However, the treatment effect was significant on CH₄ emission. The amount of total CH₄ released was the highest in the control sample followed by 2 mM SO₄ ^2- > 5 mM SO₄ ^2- > 3.2 mM NO₃^- > 5 mM NO₃^-. Methane production was decreased by more than 99 % at both 3.2 and 5 mM NO₃^- concentrations while 5 mM and 2 mM SO₄^2- decreased 90 and 78 % respectively as compared to the control. Though there were no differences found in C mineralization rate, NO₃^- was showed to be the preferred electron acceptor than sulfate. Even though NO₃^- effectively decreased the CH₄ emissions appreciable amount of N₂O also released during the C mineralization. Overall results suggest that at equivalent concentrations between NO₃^- and SO₄^2- CO₂ emissions were similar.