Abstract:

Methane (CH₄) production in oxygenated surface waters represents a biogeochemical paradox. While methane is typically produced under anoxic conditions, microbial degradation of methylated phosphonates (e.g., methylphosphonate, MPn) via C-P lyase may contribute to CH₄ supersaturation observed in oxic surface waters. This process has been experimentally confirmed mainly in oligotrophic waters (e.g., Station ALOHA in the eastern tropical North Pacific). In this talk, I will present preliminary data demonstrating aerobic methane production from methylated compounds in eutrophic to mesotrophic ecosystems, including the Pearl River Estuary, Pinqing Lagoon, and Tokyo Bay. Our experiments of size-fractionated samples (3, 0.8, 0.2 μm) from Pinqing Lagoon suggest that aerobic methane production occurs via C-P lyase of all groups. Data from Tokyo Bay suggest such activity is ubiquitous, occurring from the surface to the bottom waters with variations. The result reveals that coastal waters may be unrecognized sources of phosphonate-driven methane production, with implications for global CH₄ budgets. 

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