Oxic Methane Photoproduction in Global Great Lakes.

Lingering inconsistencies in global methane (CH4) budgets have prompted huge efforts to estimate CH4 emissions from anthropogenic and natural sources. Herein, we report the spatiotemporal patterns of the oxic CH4 photoproduction potential in global lakes and its contribution to diffusive CH4 fluxes via a remote sensing based photochemical model and lab-determined photoproduction molar ratio of CH4 to CO (ΔCH4/ΔCO). During the years 2011-2020, the oxic CH4 photoproduction potential in China's lakes (>100 km2) ranged from 2.21e-7 to 5.97e-6 mol (CH4) m-2 day-1. Deep oligotrophic lakes in western China, particularly the Tibetan Plateau, exhibited a higher CH4 photoproduction potential compared to shallow eutrophic lakes in the eastern regions. Globally, the oxic photoproduction potential of CH4 from lakes (>100 km2) averaged 1.27e-6 mol (CH4) m-2 day-1 during 2011-2020. Lakes in higher latitudes (>60°) exhibited generally lower CH4 photoproduction rates, whereas those in equatorial regions (-20° ≤ latitude ≤ 20°) and high-altitude areas (>4000 m) showed overall higher rates. It was estimated that the oxic CH4 photoproduction process of inland lakes accounted for 0.1-22% of diffusive CH4 fluxes on a global scale, and the total oxic CH4 photoproduction budget of global lakes is estimated to be 0.0104 Tg CH4/year. This study highlights the non-negligible role of the oxic CH4 photoproduction process in aquatic ecosystems, which contributes a valuable piece to the complex puzzle of global CH4 cycles.