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

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. Plain Language Summary: Lakes are highly sensitive to climate change and can produce over 30% of natural methane (CH4) emissions. However, these emissions are not well understood or included in global CH4 assessments. Current lake CH4 models either miss key processes or haven't been tested with observations from different environments. To address this, we improved the Advanced Lake Biogeochemistry Model (ALBM) to better simulate CH4 production, oxidation, and transport. We also created a new data set of CH4 emissions from 106 lakes worldwide to validate the model. Our improved model shows promising performance in simulating observed emissions. Our findings highlight the importance of including CH4 production in oxygen‐rich water, the impact of water level change on CH4 bubble release, and a new method for CH4 oxidation in lake CH4 models. The improved ALBM can now be used in Earth system models to better predict global lake CH4 emissions and their impact on climate change. Key Points: We enhanced and validated the Advanced Lake Biogeochemistry Model for lake CH4 emissions using a new global data setThe model captures lake CH4 emissions across diverse environments and accounts for seasonal and inter‐annual variationsLake CH4 models should include oxic CH4 production, water level impact on ebullition, and a new method for CH4 oxidation [ABSTRACT FROM AUTHOR]

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