Rivers are considered as an important source of methane (CH₄) to the atmosphere, but our understanding for the methanogenic pathway in rivers and its linkage with CH₄ emission is very limited. Here, we investigated the diffusive flux of CH₄ and its stable carbon isotope signature (δ¹³C-CH₄) along the river-estuary continuum of the Yangtze River. The diffusive CH₄ flux was estimated to 27.9 ± 11.4 μmol/m²/d and 36.5 ± 24.4 μmol/m²/d in wet season and dry season, respectively. The δ¹³C-CH₄ values were generally lower than -60‰, with the fractionation factor (α_c) higher than 1.055 and the isotope separation factor (ε_c) ranged from 55 to 100. In situ microbial composition showed that hydrogenotrophic methanogens accounts for over 70% of the total reads. Moreover, the incubation test showed that the headspace CH₄ concentration by adding CO₂/H₂ to the sediment was orders of magnitude higher than that by adding trimethylamine and sodium acetate. These results jointly verified the river-estuary continuum is a minor CH₄ source and dominated by hydrogenotrophic pathway. Based on the methanogenic pathway here and previous reported data in the same region, the historical variation of diffusive CH₄ flux was calculated and results showed that CH₄ emission has reduced 82.5% since the construction of Three Gorges Dam (TGD). Our study verified the dominant methanogenic pathway in river ecosystems and clarified the effect and mechanism of dam construction on riverine CH₄ emission.

河流被认为是大气中甲烷 (CH ₄ )的重要来源，但我们对河流中的甲烷生成途径及其与 CH ₄排放的联系的了解非常有限。在这里，我们调查了长江河口连续体CH ₄的扩散通量及其稳定的碳同位素特征 (δ ¹³ C-CH _{4 )。}湿季和旱季的扩散 CH ₄通量估计分别为 27.9 ± 11.4 μmol/m ² /d 和 36.5 ± 24.4 μmol/m ^{2 /d。}δ ¹³ C-CH ₄值普遍低于-60‰，分馏因子( α_c ) 高于 1.055，同位素分离因子 (ε _c ) 在 55 到 100 之间。原位微生物组成表明氢营养型产甲烷菌占总读数的 70% 以上。此外，孵育试验表明，在沉积物中添加CO ₂ /H _{2 的}顶空CH _{4浓度比添加三甲胺和乙酸钠高几个数量级。}这些结果共同验证了河流-河口连续体是CH ₄的次要来源并且以氢营养途径为主。根据此处的产甲烷途径和同一地区先前报道的数据，扩散 CH _{4的历史变化}计算通量，结果表明自三峡大坝（TGD）建设以来， CH _{4排放量减少了82.5%。我们的研究验证了河流生态系统中主要的产甲烷途径，并阐明了大坝建设对河流 CH 4}排放的影响和机制。