A Lake Biogeochemistry Model for Global Methane Emissions: Model Development, Site-Level Validation, and Global Applicability

Abstract

Lakes are important sentinels of climate change and may contribute over 30% of natural methane (CH₄) emissions; however, no earth system model (ESM) has represented lake CH₄ dynamics. To fill this gap, we refined a process-based lake biogeochemical model to simulate global lake CH₄ emissions, including representation of lake bathymetry, oxic methane production (OMP), the effect of water level on ebullition, new non-linear CH₄ oxidation kinetics, and the coupling of sediment carbon pools with in-lake primary production and terrigenous carbon loadings. We compiled a lake CH₄ data set for model validation. The model shows promising performance in capturing the seasonal and inter-annual variabilities of CH₄ emissions at 10 representative lakes for different lake types and the variations in mean annual CH₄ emissions among 106 lakes across the globe. The model reproduces the variations of the observed surface CH₄ diffusion and ebullition along the gradients of lake latitude, depth, and surface area. The results suggest that OMP could play an important role in surface CH₄ diffusion, and its relative importance is higher in less productive and/or deeper lakes. The model performance is improved for capturing CH₄ outgassing events in non-floodplain lakes and the seasonal variability of CH₄ ebullition in floodplain lakes by representing the effect of water level on ebullition. The model can be integrated into ESMs to constrain global lake CH₄ emissions and climate-CH₄ feedback.