The biological origin of methane (CH₄) has traditionally been ascribed exclusively to the activity of methanogenic archaea in anaerobic environments. However, the emergence of the “CH₄ paradox” has fundamentally challenged this paradigm, as a growing body of evidence documenting persistent CH₄ emissions from oxygenated water columns of both marine and lacustrine systems. One plausible interpretations for this paradox is the photo-decomposition of dissolved organic matter (DOM) (i.e., photo-methanification) is a previously underestimated source for aquatic CH₄ emissions. In aquatic systems, nano-sized iron (oxyhydr)oxidesare commonly found as suspended particles in aquatic systems, yet their potential influence on photo-methanification processes remains largely unknown.
          To address above knowledge gap, we conducted bench-scale experiments to investigate photo-methanification using DOM derived from a brackish cyanobacterium (Synechococcus elongatus) in the presence of idfferent iron (oxyhydr)oxides including hematite, magnetite, goethite, and ferrihydrite. Our results demonstrated that the hematite-supplemented DOM experimental system exhibited significant methanogenesis compared to the DOM-only control, with methane concentrations markedly higher than ambient background levels. And the DOM experimental systems supplemented with magnetite, goethite, and ferrihydrite exhibited marginal methanogenesis compared to the DOM-only control, with methane concentrations slightly higher than ambient background levels. These findings provide critical insights into the mechanisms driving aquatic CH₄ emissions.
 

Methane paradox; Photo-methanification; Dissolved organic matter; Reactive oxygen species; Iron oxides