Methane concentration dynamics and association with dissolved carbon in different small artificial waterbodies: Implications for origin and emission

Small artificial waterbodies (SAWs) are significant hotspots for methane (CH₄) emissions. Recent findings on CH₄ production by phytoplankton via autotrophic pathways in oxic water columns have expanded the conceptual framework of surface water CH₄ sources beyond the traditional heterotrophic pathways in anaerobic sediments. However, the mechanisms regulating CH₄ concentrations (CCH₄) in SAWs under this revised framework remain unclear. To assess the respective roles of autotrophic (dissolved inorganic carbon, DIC-driven) and heterotrophic (dissolved organic carbon, DOC-driven) pathways in driving CCH₄ across SAW types, we conducted a two-year field study during algal bloom periods in 26 SAWs, including recreational waterbodies (RWs), agricultural waterbodies (AWs), and semi-intensive aquaculture waterbodies (SIAWs). Results indicate that CCH₄ mean levels differed significantly among RWs (0.66 μmol L⁻¹), AWs (0.83 μmol L⁻¹), and SIAWs (0.38 μmol L⁻¹), corresponding to different aquatic ecosystem characteristics. In RWs and SIAWs, where humic-like substances accounted for 53.98 % and 57.27 % (means) of dissolved organic matter (DOM), respectively, CCH₄ was directly driven by DIC. In contrast, AWs, with a lower proportion of humic-like substances (mean: 43.87 %), exhibited more frequent instances of exceptionally high methane emission fluxes values—estimated using the static chamber method—likely due to ebullition from sediments, with CCH₄ was directly driven by DOC. DOM characteristics serves as a common indirect influencing factor on CCH₄. These results highlight the direct role of the phytoplankton methane production pathway in driving CCH₄ with a high degree of DOM degradation.