Riverine Carbon Dioxide Release in the Headwater Region of the Qilian Mountains, Northern China

Rivers are important sources of the carbon dioxide (CO₂) released into the atmosphere; however, research on CO₂ fluxes from riverine headwater regions is sparse, particularly from rivers from in the Tibetan Plateau (TP) region, which has large glaciers and permafrost. We conducted a three-year (2020–2022) observational study of CO₂ fluxes from the riverine headwater region of the Qilian Mountains (QLMs) to determine diurnal and seasonal CO₂ variations and fluxes. Our results revealed that the annual average CO₂ emission was 0.45 (0.03–1.60) kg m^–2 yr^–1, with the highest fluxes observed in winter [0.87 (0.08–2.67) μmol m^–2 s^–1], which was approximately three times higher than fluxes in other seasons. Glacier meltwater altered the diurnal pattern of riverine CO₂ fluxes by diluting CO₂ and dissolved inorganic carbon. Meanwhile, CO₂ release from rivers in the permafrost region was dictated by river order, with a linear decrease as river order increased. Considering diurnal and seasonal variations, the total CO₂ fluxes from the headwater regions of the QLMs were approximately 39.57 (30.04–50.21) Gg C yr^–1, representing 76% of the pre-calibration fluxes. This study provides essential insights into CO₂ release from headwaters, which have substantial implications for understanding CO₂ outgassing.