Riverine carbon dioxide release in the headwater region of the Qilian Mountains, northern China.

• The CO 2 fluxes in winter were three times higher than in other seasons. • Glacier meltwater altered the diel pattern of CO 2 fluxes. • The total CO 2 fluxes from the headwaters were 39.57 (30.04–50.21) Gg C yr−1, ignoring the diurnal variation overestimated the CO 2 fluxes. • The CO 2 fluxes from 1st and 2nd order streams accounted for 77% of the headwaters. Rivers are important sources of the carbon dioxide (CO 2) released into the atmosphere; however, research on CO 2 emission from riverine headwater regions is sparse, particularly from rivers in the Tibetan Plateau (TP) region, which has large area of glaciers and permafrost. We conducted a three-year (2020–2022) observational study of CO 2 flux rates from the riverine headwater region of the Qilian Mountains (QLMs) to determine diel and seasonal CO 2 variations and flux rates. Our results revealed that the annual average CO 2 emission was 0.45 (0.03–1.60) kg CO 2 m−2 yr−1, with the highest flux rates observed in winter [0.87 (0.08–2.67) μmol CO 2 m−2 s−1], which was approximately three times higher than flux rates in other seasons. Glacier meltwater altered the diel pattern of riverine CO 2 flux rates by diluting CO 2 and dissolved inorganic carbon. Meanwhile, CO 2 release from rivers in the permafrost region was dictated by stream order, with a linear decrease as stream order increased. Considering diel variations, the total CO 2 fluxes from the headwater regions of the QLMs were approximately 32.70 (25.00–41.28) Gg C/yr, representing 76 % of the pre-calibration total CO 2 fluxes ignoring diel variations. This study provides essential insights into CO 2 release from headwaters, which have substantial implications for understanding CO 2 outgassing. [ABSTRACT FROM AUTHOR]