Oxic Methane Photoproduction in Global Great Lakes

Area of Science:

• Environmental Science
• Biogeochemistry
• Remote Sensing

Background:

• Global methane (CH4) budgets have inconsistencies, necessitating better estimation of CH4 emissions from various sources.
• Aquatic ecosystems, particularly lakes, are significant sources of atmospheric methane, but their contributions are not fully quantified.
• The role of oxic methane photoproduction in lakes remains understudied despite its potential contribution to overall CH4 budgets.

Purpose of the Study:

• To investigate the spatiotemporal patterns of oxic methane (CH4) photoproduction potential in global lakes.
• To quantify the contribution of oxic CH4 photoproduction to diffusive CH4 fluxes in lakes.
• To estimate the global CH4 budget from oxic photoproduction in lakes.

Main Methods:

• Utilized a remote sensing-based photochemical model to assess oxic CH4 photoproduction potential.
• Employed lab-determined photoproduction molar ratios of CH4 to CO (ΔCH4/ΔCO) for flux calculations.
• Analyzed data for lakes larger than 100 km² globally from 2011-2020.

Main Results:

• Oxic CH4 photoproduction potential in China's lakes (2011-2020) varied spatially, with higher rates in deep, oligotrophic western lakes compared to shallow, eutrophic eastern lakes.
• Globally, average oxic CH4 photoproduction potential in lakes was 1.27e-6 mol (CH4) m⁻² day⁻¹ (2011-2020).
• Lakes in equatorial regions and high-altitude areas showed higher rates, while higher-latitude lakes had lower rates. Oxic photoproduction accounted for 0.1-22% of diffusive CH4 fluxes, totaling an estimated 0.0104 Tg CH4/year globally.

Conclusions:

• Oxic methane (CH4) photoproduction is a significant, previously underestimated process in aquatic ecosystems.
• This process plays a non-negligible role in the global methane cycle, contributing to the overall CH4 budget.
• The findings provide crucial data for refining global CH4 budgets and understanding aquatic CH4 emissions.