Methane dynamics in the Hailuogou Glacier forefield, Southwest China

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 CO_2, 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 (J_atm) using the concentration gradient method based on the soil CH₄ concentration, sampling depth, and soil porosity. J_atm 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).