Methane oxidation and diffusivity in mollisols under an urban forest in Argentina

Abstract

Methane (CH4) oxidation in aerated soils is regulated mainly by physical factors which limit CH4 diffusion into the soil. Using the static chamber technique, we measured CH4 flux at the soil-atmosphere interface (SAI) and estimated its diffusivity (DsCH4) in a plantation of mixed deciduous species during a year. Methane diffusivity (DsCH4) was determined through two in situ techniques (Fick´s Law -FL- and SF6 methods) and a particular soil parameter model (SP method). Mean CH4 oxidation was 15.61 ± 6.39 ng CH4/m2/s and varied significantly among seasons, coinciding with variation in soil water content (W%) (R = -0.8697, p = 5 × 10−4). CH4 diffusivity presented mean values of 0.0151 ± 0.0085 cm2/s and 0.0173 ± 0.0070 cm2/s for SP and FL methods respectively, and 0.0222 ± 0.0093 cm2/s for SF6 method, with a statistically significant difference from the other two (p < 0.05). For the three methods, temporal variation in CH4 diffusion exhibited the same response as CH4 oxidation and a good negative linear correlation was found between W% and DsCH4 (p < 0.01). Results suggest that Fick´s Law could be used for a first estimation of CH4 oxidation and that, in this temperate region, SP is the most appropriate method to obtain a first approximate measure of DsCH4 (R = 0.83, p = 0.001).