Groundwater-derived carbon stimulates headwater stream CO₂ emission potential on the Qinghai-Tibet Plateau

CO₂ emissions from headwater streams are a crucial component of greenhouse gas flux in inland waters. However, the influence of groundwater, a major contributor to streams in the Asian Water Tower (Qinghai-Tibet Plateau, QTP), on CO₂ levels remains unclear. This study employed stable isotope analysis and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS) to demonstrate that groundwater-derived dissolved inorganic carbon (DIC) significantly enhanced CO₂ supersaturation in the Shuiluo stream on the QTP. Specifically, the partial pressure of CO₂ (pCO₂), indicative of CO₂ emission potential, increased more than threefold to 1,615 ± 495 μatm in groundwater-rich sites, nearly one time higher than the mean value (843 μatm) across the QTP. Groundwater-derived carbonate weathering had a significant impact of 76.6 % on the increased pCO₂, whereas the degradation of highly unsaturated polyphenolics with high O/C contributed to 15.8 %. The estimated inflow of groundwater-derived DIC could reach 9.59 ± 0.34 Tg C/y in total runoff across the QTP, highlighting significant CO₂ sources. This study presents new findings on the effects of groundwater-derived DIC on stream CO₂ emissions in weathered regions and expands our knowledge of fluvial CO₂ emissions on the QTP.