湖からのメタン放出動態をグローバルモデルに反映（Improving the Representation of Methane Dynamics in Global Lake Models）

2025-07-10

2025-07-09 パシフィック・ノースウェスト国立研究所 (PNNL)

パシフィック・ノースウェスト国立研究所（PNNL）の研究チームは、湖沼が放出するメタン（CH₄）の動態をより正確に再現するため、湖沼生物地球化学モデル「ALBM」を改良。新たに酸素存在下でのメタン生成（OMP）や放出量に影響を与える水位変動など複雑な過程を組み込み、106湖の観測データで検証した。結果、従来モデルより季節・年次変動を高精度に再現し、OMPが表層放出に重要な役割を果たすことを確認。本モデルは、初の地球システムモデル（ESM）統合可能な湖沼CH₄モデルとして、気候変動予測の精度向上に貢献が期待される。

＜関連情報＞

世界的なメタン排出のための湖沼生物地球化学モデル：モデル開発、サイトレベルでの検証、そしてグローバルな適用性 A Lake Biogeochemistry Model for Global Methane Emissions: Model Development, Site-Level Validation, and Global Applicability

Zeli Tan, Huaxia Yao, John Melack, Hans-Peter Grossart, Joachim Jansen, Sivakiruthika Balathandayuthabani, Khachik Sargsyan, L. Ruby Leung
Journal of Advances in Modeling Earth Systems Published: 27 October 2024
DOI:https://doi.org/10.1029/2024MS004275

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.

Key Points

We enhanced and validated the Advanced Lake Biogeochemistry Model for lake CH₄ emissions using a new global data set
The model captures lake CH₄ emissions across diverse environments and accounts for seasonal and inter-annual variations
Lake CH₄ models should include oxic CH₄ production, water level impact on ebullition, and a new method for CH₄ oxidation

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.