[A-HW27] Biodiversity, nutrients and other materials in ecosystems from headwaters to coasts

[AHW27-02] Methane dynamics and oxidation in tropical maar lakes: The Influence of stratification, mixing, and microbial communities

★Invited Papers

*Milette Mendoza Pascual¹, Justine R De Leon^2,3, Sarah Jewel De Leon⁴, Ryamico Reyes⁴, Kamille N Poblete⁴, Tzu-Hsuan Tu^5,6, Wan Ting Chen⁵, Mark Louie D Lopez⁷, Yuki Kobayashi⁸, Fuh-Kwo Shiah⁹, Pei-Ling Wang^10,14, Li-Hung Lin^5,10, Masayuki Itoh¹¹, Noboru Okuda^8,12,13, Rey Donne S Papa^2,4,3 (1.Ateneo Research Institute for Science and Engineering; Department of Environmental Science, School of Science and Engineering, Ateneo de Manila University, Quezon City, Philippines, 2.Research Center for the Natural and Applied Sciences, University of Santo Tomas, Manila, Philippines,, 3.Department of Biological Sciences, College of Science, University of Santo Tomas, Manila, Philippines, 4.The Graduate School, University of Santo Tomas, Manila, Philippines, 5.Department of Geosciences, National Taiwan University, Taipei, Taiwan, 6.Department of Oceanography, National Sun Yat-sen University, Kaohsiung, Taiwan, 7.Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC, Canada, 8.Center for Ecological Research, Kyoto University, Shiga, Japan, 9.Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan, 10.Research Center for Future Earth, National Taiwan University, Taipei, Taiwan, 11.Research Institute for Sustainable Humanosphere, Kyoto University, Kyoto, Japan, 12.Research Center for Inland Seas, Kobe University, Kobe, Japan, 13.Research Institute for Humanity and Nature, Kamigamo Motoyama, Kita Ward, Kyoto, Japan, 14.Institute of Oceanography, National Taiwan, University, Taipei, Taiwan)

Keywords:tropical lakes, methane potential emission, methanotrophs

Methane (CH₄) emissions from freshwater ecosystems are a significant contributor to global greenhouse gas fluxes, yet the dynamics governing CH₄ storage, release, and oxidation in tropical lakes remain underexplored. This work integrates findings from two investigations on CH₄ dynamics and methane-oxidizing bacterial communities (MOB) in three maar lakes in the Philippines. CH₄ concentrations were found to be strongly influenced by lake depth, stratification, and mixing regimes, with deeper lakes storing higher CH₄ levels in their anoxic profundal layers. While shallow lakes exhibited CH₄ fluctuations driven by atmospheric pressure changes, deeper lakes remained largely unaffected by daily weather variations. Concurrently, molecular analyses of MOB communities revealed disctinct seasonal and depth-related variations in microbial composition. Proteobacterial Type I and Type II MOB, along with Verrucomicrobial and NC10 taxa, played a crucial role in CH₄ oxidation, with Type I MOB responding notably to monsoon-induced mixing. The combined findings highlight the interplay between physical and biological CH₄ processes, emphasizing the importance of lake stratification and microbial activity in regulating CH₄ emissions from tropical lakes. Understanding these dynamics is essential for refining global CH₄ emission estimates and assessing the role of microbial mitigation in tropical freshwater systems.