Improving the Representation of Methane Dynamics in Global Lake Models
Schematic of the improved Advanced Lake Biogeochemistry Model (ALBM) developed in this study. This figure illustrates the numerous complex, methane-involved processes that occur in lakes. Accurately capturing methane (CH4) emissions from lakes is important to constrain the climate-CH4 feedback in Earth system models but has thus far been a missing component. Figure from Tan et al. (2024).
Figure from Tan et al. (2024)
Current lake CH4 models either miss key processes or haven’t been tested with observations from diverse environments. Further, no Earth system model (ESM) has yet represented lake CH4 dynamics. This study, therefore, improved the Advanced Lake Biogeochemistry Model (ALBM) by including new modeling methods for CH4 production, oxidation, and transport. The team also created a new dataset of CH4 emissions from 106 lakes worldwide for model validation. The results indicated that oxic methane production (OMP)—a process not currently included in lake CH₄ models, whereby methane is generated in the surface waters of a lake—plays a significant role in overall CH₄ diffusion. The improved model showed overall strong performance in simulating observed emissions at seasonal and inter-annual timescales and from the lakes on different continents.
Lakes are highly sensitive to climate change and can produce over 30% of natural CH4 emissions, which affect global warming levels and the ozone layer, among others. Despite its importance, lake emissions are one of the most uncertain CH4 sources in the global CH4 assessment and have not been represented in any ESMs. By reproducing the observed CH4 emissions from 106 lakes in diverse environments, the improved ALBM could become the first lake CH4 model that can be integrated into ESMs to constrain global lake CH4 emissions and climate-CH4 feedback. The study also develops several new modeling methods for CH4 production, oxidation, and transport that can help improve the global applicability of other lake CH4 models.
Lakes are important sentinels of climate change and contribute significantly to the emissions of the second most important greenhouse gas—CH4. However, no ESM has represented lake CH4 dynamics. To fill this gap, this study improved the process-based ALBM. This included adding and/or refining the representation of lake bathymetry, OMP, the effect of water level on ebullition, new CH4 oxidation kinetics, and the coupling of sediment carbon with lake primary production and upstream carbon loadings. Researchers also compiled a global dataset of lake CH4 emissions for model validation. The improved ALBM reproduces 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 from 106 lakes across the globe. The results suggest that OMP, a newly discovered process, could play an important role in surface CH4 diffusion, and its relative importance is higher in less productive and/or deeper lakes. The effect of water level on ebullition is important for CH4 outgassing in lakes of significant water level fluctuations, such as floodplain lakes. Future research will be conducted to integrate the model into the Energy Exascale Earth System Model (E3SM) to constrain global lake CH4 emissions and climate-CH4 feedback.