Study On CO₂ Fluxes And Its Influencing Factors From Rivers In Headwater Regions On The Qilian Mountains

The study of carbon dioxide（CO₂）released from rivers in headwater regions is limited,particularly in the Asian Rivers originating from the Qinghai-Tibet Plateau（QTP）.The Qilian Mountains（QLMs）are an important study area for CO₂ release in headwater regions.However,the studies on CO₂ release in this region are insufficient.This study presents a 3-year observational research on CO₂ release and water quality parameters in headwater region of QLMs.The study analyzes the areal and total fluxes of CO₂ release from rivers in the QLMs,the temporal and spatial variation patterns of CO₂ release,the influencing factors of CO₂ release,and the mechanism of glaciers and permafrost on CO₂ release.The results provide important insights into the poorly studied region and can be used to accurately assess CO₂ release from rivers and its climatic effects over the QTP.Additionally,the study has significant implications for understanding CO₂ exchange at the water-gas interface of headwaters.Overall,the study findings shed light on the importance of understanding the CO₂ release from rivers in headwater regions,particularly in high-altitude areas such as the QTP.The main findings are as follows.（1）Diurnal CO₂ release characteristics were studied at the Qilian Station and Hulugou sections,revealing significant differences between the two sections.Daytime release at the Qilian Station section was 2.2 times larger than nighttime release,while the opposite was observed at the Hulugou section.Winter had the most significant CO₂release from rivers in the headwater region on the QLMs,being three times larger than other seasons.Total CO₂ fluxes during the river ice thawing period accounted for 25%of the annual release from the upper Heihe River and were 0.72 Gg C yr^-1.CO₂ fluxes decreased with increasing river order,with similar spatial variability observed in CO₂release from the upper Heihe River and the Sara River.（2）The rivers in the headwater region on the QLMs were found to be sources of CO₂,releasing an average of 40.42（5～95th percentiles:4.92～119.53）Gg C yr^-1.The total CO₂ fluxes from the upper Heihe River and the Sara River were 2.43（0.34～6.89）Gg C yr^-1 and 0.07（0～0.17）Gg C yr^-1,respectively,with the total CO₂ fluxes from the upper Heihe River being more significant than that from the Sara River.Areal fluxes of CO₂ were not significantly different between the upper Heihe River and the Sara River.Areal CO₂ fluxes were 0.33（0.03～1.21）μmol m^-2 s^-1 and 0.36（0.02～1.00）μmol m^-2 s^-1 for the upper Heihe River and the Sara River,respectively.（3）This study examined the correlation between CO₂ release and dissolved components（DOC,DIC,and TDN）and environmental variables（p H,water temperature,DO,altitude,and percentage of permafrost area）in headwater region of the QLMs to investigate the patterns and mechanisms associated with these elements on river CO₂ release.Results indicated that seasonal variation（winter>autumn>spring>summer）in the headwater rivers was mainly influenced by chemical weathering,photosynthesis,carbonate balance,and groundwater recharge.The spatial variation was mainly influenced by turbulence,flow velocity,width,depth,elevation,permafrost,and groundwater recharge.（4）The recharge of the river by glacial melt influenced CO₂ release from the Hulugou section of the upper Heihe River.Results showed that CO₂ release was minimum at 5 pm and maximum at 3 am.During the day,glacial melt diluted CO₂ and DIC concentrations in the river causing a decrease in CO₂ release.At night,the recharge of glacial melt decreased,leading to an increase in CO₂ release.Permafrost regulated riverine CO₂ release in the headwater region on the QLMs,mainly through riverine DIC concentrations,resulting in increased CO₂ release as the percentage of permafrost area increased.