Methane emissions from the riverine sandy wetlands on the Mongolia Plateau

Methane (CH₄) processes and fluxes have been widely investigated in low-latitude tropical wetlands and high-latitude boreal peatlands. In the mid-latitude Mongolia Plateau, however, CH₄ processes and fluxes have been less studied, particularly in riverine wetlands. In this study, in situ experiments were conducted in the riverine sandy wetlands of the Mongolia Plateau to gain a better understanding of CH₄ emissions and their influencing mechanisms. Annual CH₄ emissions were observed at 8.7 mg m^-2 h^-1 from the flowing water wetlands during November 2019 - October 2021, approximately 80% and 20% of which were emitted during the growing and non-growing seasons, respectively. In particular, CH₄ emissions during the thawing period contributed < 5% to the annual total, contrary to the traditional idea that thawing plays an important role in annual CH₄ emissions in boreal peatlands. CH₄ emissions were significantly higher in the wetlands dominated by plant species than in that dominated by water body during the growing seasons; therefore, plant-mediated CH₄ transport was explained as a favorable pathway for CH₄ emissions from sandy soils to the atmosphere. Gene sequencing revealed differences in the phylogenies and taxonomies of methanogenic archaea and methanotrophs between the flowing and static water wetlands, suggesting that flowing water should bring oxygen and nutrients to microbial habitats and potentially affect the production, oxidation, and diffusion of CH₄ in sandy wetlands.