Winter CH4 oxidation in cold-temperate grassland soils of northern Japan: 222Rn as a proxy for the validation of CH4 diffusivity

• Published in: Polar Science
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Winter methane oxidation; CH4 diffusivity; Rn-222 tracer; Snowpack; Cold temperate soils; Polar Science
• Online Access: https://nipr.repo.nii.ac.jp/?action=repository_uri&item_id=16819; http://id.nii.ac.jp/1291/00016689/

Amidst changing seasonal snow-covered periods and extents in northern high latitude regions, winter CH4 oxidation is susceptible to drastic climate change, all of which modulates an accurate assessment of regional carbon balance. The importance of winter CH4 oxidation to the soils in these regions has previously been recognized; in this study, concentrations of CH4 and 222Rn were observed in the snowpack and underlying cold temperate soils during the winters of 1995/96 and 1996/97. These observations were carried out in order to 1) validate the 222Rn tracer as a proxy for variations in CH4 diffusivity within a snowpack containing many seasonal ice lenses, and to 2) estimate winter CH4 oxidation through the snowpack to the soils. Winter CH4 oxidations estimated by snow density (method 1); using the 222Rn tracer under steady (method 2) and non-steady (method 3) conditions; and using a static chamber (method 4) during the winter of 1996/97 yielded 16.7 ± 6.3; 8.2 ± 2.9; 9.8 ± 7.4; and 4.5 ± 2.5 mg CH4–C m−2, respectively. These results suggest that contributions from average CH4 oxidation represent 23.3% (range: 12.7–35.1%) of the annual CH4 oxidation into cold temperate soils. Wintertime CH4 oxidation significantly reflects temporal variation in the snowpack, demonstrating that soil temperature depends on snow cover, and that a threshold snow depth of 40 cm does not prevent, but rather promotes, atmospheric CH4 oxidation through snowpack to the soils. These findings demonstrate that the 222Rn tracer was useful for estimating winter CH4 diffusivity and oxidation, using a one-dimensional vertical diffusion box model in cold temperate soils in Japan during multiple snow-covered seasons.