Seasonal Variability in Atmospheric-Methane Oxidation in a Swiss Glacier Forefield

Abstract:

Aerobic methane (CH₄) oxidation in upland soils is the only known terrestrial sink for atmospheric CH₄. However, a comprehensive understanding of the magnitude and dynamics of CH₄ turnover and flux in developing soil ecosystems such as glacier forefields is still lacking. Glacier forefields progressively formed as a result of glacier recession feature various landforms with different physicochemical properties, which may affect CH₄ turnover and flux. In addition, CH₄ turnover and flux depend on a variety of environmental factors including soil-water content and -temperature, which typically follow seasonal patterns. In this study we investigated the variability in atmospheric CH₄ turnover and associated soil-atmosphere flux in a Swiss glacier forefield during the snow-free season and on different landforms including sandhill, terrace, and floodplain. Turnover and soil-atmosphere CH₄ flux was quantified using the soil-profile method and static flux chambers. To achieve high temporal resolution, nine sampling campaigns were performed. Turnover and flux measurements indicated substantial CH₄ uptake on the sandhill (up to -0.69 mg CH₄ m^-2 d^-1), with highest uptake observed early in the season. There was a noticeable trend for decreasing CH₄ uptake with ongoing season. Conversely, CH₄ flux on terrace and floodplain (avg. < -0.1 mg CH₄ m^-2 d^-1) was substantially smaller than on the sandhill, and some individual flux chambers on terrace and floodplain even indicated intermittent CH₄ emission. Our findings indicate that CH₄ turnover and soil-atmosphere flux in glacier forefields may vary substantially during the snow-free season, and that there are substantial differences in CH₄ flux between different glacier-forefield landforms.