Methane-limited methanotrophy in tidal freshwater swamps

Abstract

We investigated the relationship between CH4 production and oxidation in two tidal freshwater wetland forests in order to determine whether CH4 oxidation efficiency was limited by O2 or CH4. Methane oxidation was measured in situ over a 16-month period with bi-monthly applications of the inhibitor CH3F. Oxidation consumed 52 ± 10 and 81 ± 9% of diffusive CH4 emissions on the two sites. Methane oxidation rates were linearly related to gross CH4 emissions on both sites (r2 = 0.96), demonstrating the process was CH4-limited. This interpretation is consistent with the fact that the apparent activation energies for the potential CH4 production and oxidation differed by <4 kJ mol-1. Apparent activation energies calculated from field emissions data were also similar for the two processes. The high CH4 oxidation efficiency on these sites may be attributed to relatively low rates of methane production, a deep oxidizing zone (5-10 cm), and low cover of understory vegetation capable of CH4 transport. If our results are typical of forested wetlands, CH4 oxidation efficiency in forested wetlands will not change in response to soil warming.