Microbial Oxidation and Vertical Stratification Regulate Methane Emission in Geothermal and Non-Geothermal Lakes on the Tibetan Plateau

Methane (CH₄) is a potent greenhouse gas， and inland lakes are increasingly recognized as significant natural sources. While most lake CH₄ studies focus on surface fluxes， vertical processes that regulate CH₄ production， transport， and oxidation remain poorly understood， especially in high-altitude lakes on the Tibetan Plateau （TP）. We investigated 13 TP lakes， spanning freshwater to hypersaline and geothermal to non-geothermal systems. Measurements included vertical profiles of dissolved CH₄concentration (dCH₄)， methane isotopic composition (δ¹³C-CH₄)， surface CH₄ fluxes， environmental parameters （temperature， salinity， dissolved oxygen）， and gene abundances of methanogens and methanotrophs. Geothermal lakes exhibited strong thermal and salinity stratification， leading to high CH₄ accumulation in bottom waters (up to 22.6 μmol·L^-1)， but low surface emissions due to efficient oxidation in oxygen-rich mid-depth layers. Methane isotopic signatures and gene data suggest mixed thermogenic and microbial CH₄ sources. In contrast， non-geothermal had weaker stratification， more uniform dCH₄ profiles， and higher surface fluxes， primarily driven by microbial production. Our findings highlight a “high production-low emission” pattern in geothermal lakes， driven by the combined effects of stratification and microbial oxidation. Integrating these factors into carbon flux models is essential for improving global CH₄ budgets， especially in high-elevation or hydrothermally active regions.