Methane dynamics in the Hailuogou Glacier forefield, Southwest China.

Soils in glacier forefields have a significant capacity for atmospheric CH 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 CH dynamics and their potential regulatory factors, we measured the concentrations and stable carbon (C) isotope compositions of CH and CO soil physicochemical properties, and perfromed a high-throughput sequencing. Among nine sampling sites, soil CH concentrations of six sites were below atmospheric levels and δC-CH values were similar to atmospheric levels. The average value was approximately -48.6‰ and without obvious fractionation. The soil CH concentrations exceeded atmospheric levels for the remaining three sites, and the δC-CH values were more enriched with increasing soil CH concentration. We calculated the soil-atmosphere CH flux (J) using the concentration gradient method based on the soil CH concentration, sampling depth, and soil porosity. J ranges from -0.08 to -0.52 mg m d, acting as an atmospheric CH sink. It also shows that the correlation with soil exposure age or vegetation succession was insignificant. But the CH emission shows a larger variation changing from 0.05 to 1.8 mg m d, which could result from local CH production differences catalyzed by aceticlastic methanogens. The results showed that not all sites acted as a net CH sink. SWC may have an important influence on CH dynamics in the Hailuogou Glacier forefield (HGF).