Separating methane production and consumption with a field-based isotope pool dilution technique

[1] Despite the importance of methane for climate, it has remained difficult to measure gross rates of methane production and consumption without inducing artifacts. To remedy this, we have developed, tested, and applied a field-based (CH4)-C-13 pool dilution technique. Laboratory tests, sensitivity analyses, and field data indicate that this technique is robust for measuring gross rates of methane production and consumption. In our analyses of 130 soil cores from 17 field sites of differing environmental conditions, we encountered a wide range of gross methane production rates (0.04-930 mg CH4-C m(-2) day(-1)), but encountered a narrower range of consumption rates (0.1-9.2 mg CH4-C m(-2) day(-1)). Unexpectedly, we found that gross production of methane was common (mean = 0.15 mg CH4-C m(-2) day(-1)) even in dry, oxic soils where average soil conditions cannot support methane producers. Through improved measurement of methane turnover in soils, this technique can offer a more fine-grained understanding of how productive and consumptive processes are linked to soil-atmosphere trace gas balances.