Although numerous studies have investigated CH₄ emissions from river systems globally, observational data remain scarce for transboundary rivers in southwestern China. Focusing on the Yunnan section of the Irrawaddy River, this study carried out cross-seasonal sampling from October 2022 to December 2023. Dissolved CH₄ concentrations in the river surface water were measured using the headspace equilibrium technique, while diffusive CH₄ fluxes across the water–air interface were quantified using the floating chamber method. The spatiotemporal distribution patterns of CH₄ and their controlling factors were systematically analyzed. The results showed that riverine CH₄ concentrations ranged from 5.6 to 476.5 nmol/L, with a mean concentration of 64.0±98.4 nmol/L. The river was consistently supersaturated with CH₄ relative to the atmosphere (mean: 2213%±3498%; range: 162%–17024%). Diffusive CH₄ fluxes ranged from 0.004 to 1.22 mmol/(m²∙d), with a mean flux of 0.26±0.22 mmol/(m²∙d). CH₄ concentrations were higher in spring and summer, yet lower in autumn and winter. Diffusive fluxes exhibited a distinct seasonal pattern, being highest in spring and lowest in summer. Analysis of environmental drivers revealed that dissolved organic carbon (DOC), acting as a carbon substrate, was present at low concentrations, potentially limiting CH₄ production. Concurrently, suspended sediments in the water column appeared to inhibit the diffusive release of CH₄. Comparative analysis with CH₄ observations from other subtropical rivers indicated that both the concentration and diffusive flux of CH₄ in the Yunnan section of the Irrawaddy River were relatively low overall. Consequently, this river section functions as a weak source of atmospheric CH₄. 

针对中国西南地区跨境河流甲烷(CH₄)观测资料较为缺乏的问题, 聚焦伊洛瓦底江云南段, 于2022年10月至2023年12月开展为期一年的跨季节采样, 通过顶空平衡法测定河流表层CH₄浓度, 结合浮箱法测定水−气界面CH₄扩散通量, 系统地分析其时空分布特征及其影响因素。结果显示, 河流CH₄浓度范围为5.6~476.5 nmol/L, 平均浓度为64.0±98.4 nmol/L, 相对于大气为过饱和状态(162%~17024%, 均值为2213%±3498%)。CH₄扩散通量范围为0.004~1.22 mmol/(m²∙d), 平均通量为0.26±0.22 mmol/(m²∙d)。CH₄浓度春夏季较高, 秋冬季较低; 扩散通量则表现为春季高、夏季低的特征。环境因子分析结果表明, 作为碳源, 溶解性有机碳(DOC)的浓度较低, 限制CH₄的产生; 同时, 水体中悬浮泥沙抑制CH₄的扩散和释放。与其他亚热带河流的CH₄观测结果相比, 伊洛瓦底江云南段河流的CH₄浓度和扩散通量整体上偏低, 表现为大气CH₄的弱源。