Soils in glacier forefields have a significant capacity for atmospheric CH4 uptake, but this pattern could be changed by high soil water content (SWC). The Hailuogou Glacier in SW China is a typical temperate monsoon glacier on siliceous bedrock, where a forefield soil chronosequence has developed with progressive glacier recession. To understand CH4 dynamics and their potential regulatory factors, we measured the concentrations and stable carbon (C) isotope compositions of CH4 and CO2, soil physicochemical properties, and perfromed a high-throughput sequencing. Among nine sampling sites, soil CH4 concentrations of six sites were below atmospheric levels and δ13C-CH4 values were similar to atmospheric levels. The average value was approximately -48.6‰ and without obvious fractionation. The soil CH4 concentrations exceeded atmospheric levels for the remaining three sites, and the δ13C-CH4 values were more enriched with increasing soil CH4 concentration. We calculated the soil-atmosphere CH4 flux (Jatm) using the concentration gradient method based on the soil CH4 concentration, sampling depth, and soil porosity. Jatm ranges from -0.08 to -0.52 mg m-2 d-1, acting as an atmospheric CH4 sink. It also shows that the correlation with soil exposure age or vegetation succession was insignificant. But the CH4 emission shows a larger variation changing from 0.05 to 1.8 mg m-2 d-1, which could result from local CH4 production differences catalyzed by aceticlastic methanogens. The results showed that not all sites acted as a net CH4 sink. SWC may have an important influence on CH4 dynamics in the Hailuogou Glacier forefield (HGF).
Keywords: Carbon isotope; Hailuogou Glacier forefield; Methane dynamics; Methane flux; Soil water content.
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