[sup 13]C/[sup 12]C fractionation of methane during oxidation in a temperate forested soil

The authors have made measurements of the [sup 13]C/[sup 12]C fractionation of methane (CH[sub 4]) during microbial oxidation by an upland temperate soil from College Woods, New Hampshire, using both in situ and laboratory incubation measurements. Uptake rates of 1-4.8 mg CH[sub 4]/m[sup 2]/d were measured during the active season in New Hampshire while rates of uptake were 2.6-6.8 mg CH[sub 4]/m[sup 2]/d in jars used for incubation studies. The fractionation factor, calculated from field measurements, was [alpha] = 0.978 [+-] .004. This corresponds to a kinetic isotope effect (KIE) of K[sub 12]/k[sub 13] = 1.022 [+-] .004. Only a small dependence on temperature was noted for air temperatures between 281 and 296 K. The results indicate that the KIE of soil CH[sub 4] oxidation is controlled by physical parameters based on gaseous diffusion into the soil. The implications of these results are discussed with respect to the global CH[sub 4] budget, and balancing CH[sub 4] sources and sinks through the use of [delta][sup 13]CH[sub 4] measurements.