CH4 and CO2 emissions and dissolved carbon exporting in rivers on the upper Lanzhou section of the Yellow River, China

• Upper Lanzhou section of the Yellow River was moderate for CH 4 and CO 2 emitters. • The artificial wastewater was hotspot for CO 2 emitter. • Ebullition was a major pathway of CH 4 emission, accounted for 53.1 % ± 22.4 %. • Acetoclastic methanogenesis is dominant CH 4 production pathway. The Yellow River (YR), China’s second-longest river, remains understudied regarding its greenhouse gases (GHGs) emissions, particularly the impacts of urban drainage ditches and wastewater treatment facilities on regional GHGs dynamics. This study investigated methane (CH 4 ) and carbon dioxide (CO 2 ) concentrations, fluxes and stable carbon isotopes ( δ 13 C-CH 4 and δ 13 C-CO 2 ) across six main stream, three ditches, and one wastewater treatment site along the upper Lanzhou section of the YR, spanning from the urban entrance (36.176°N, 103.449°E) to the exit of Lanzhou city (36.056°N, 104.020°E). Measured CH 4 diffusion fluxes in mainstem sites ranged from 0.01 to 2.58 mmol·m −2 ·d −1 (mean: 0.36 mmol·m −2 ·d −1 ), while ebullitive fluxes (gas bubbles) ranged from 0.01 to 18.89 mmol·m −2 ·d −1 (mean: 0.90 mmol·m −2 ·d −1 ). CO 2 diffusion fluxes varied between 9.16–92.80 mmol·m −2 ·d −1 (averaged: 39.11 mmol·m −2 ·d −1 ) at these locations. Ebullition (bubble) fluxes accounted for 53.1% ± 22.4% (range: 9.0% to 98.4%) to total CH 4 emissions (diffusion plus ebullition), with peak fluxes occurring during summer, indicating its significance as a CH 4 transport mechanism. Notably, both diffusion CH 4 and CO 2 fluxes and ebullitive CH 4 rates at ditch sites substantially exceeded those in mainstream reaches. The lowest CH 4 and highest CO 2 concentrations were observed at a wastewater treatment site, likely resulting from the removal of high organic loads. Acetoclastic methanogenesis—the process converting acetate-derived methyl groups to CH 4 —was identified as the dominant production pathway in both mainstream and ditch environments. CH 4 and CO 2 flux magnitudes in the upper YR (Lanzhou section) were comparable to those observed in subtropical Yangtze River tributaries. These results demonstrate that anthropogenic influences significantly enhance CO 2 /CH 4 emissions, and the lateral exports of dissolved carbon (DIC and DOC) in the main stream site was quantified., which cannot be overlooked. The findings emphasize the critical need to account for pronounced spatiotemporal variations in arid-region GHG fluxes to improve basin-scale estimates for the YR.