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.
Keywords: CO(2) partial pressure; FT-ICR MS; Groundwater; Headwater stream; Isotope analysis.
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