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 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 CO2 flux rates from the riverine headwater region of the Qilian Mountains (QLMs) to determine diel and seasonal CO2 variations and flux rates. Our results revealed that the annual average CO2 emission was 0.45 (0.03-1.60) kg CO2 m(-2) yr(-1), with the highest flux rates observed in winter [0.87 (0.08-2.67) mu mol CO2 m(-2) s(-1)], which was approximately three times higher than flux rates in other seasons. Glacier meltwater altered the diel pattern of riverine CO2 flux rates by diluting CO2 and dissolved inorganic carbon. Meanwhile, CO2 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 CO2 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 CO2 fluxes ignoring diel variations. This study provides essential insights into CO2 release from headwaters, which have substantial implications for understanding CO2 outgassing.