[Spatial Variations of CO₂ Degassing Across Water-air Interface and Its Impact Factors in Summer in Guijiang River,...

River is characterized by obvious spatial heterogeneity in catchment, which is exacerbated by special environment features of calcium-rich, alkaline and DIC-rich(dissolved inorganic carbon) in karst river. Thus, it also leads to significant spatial variation in the CO₂ degassing across water-air interface. Main ions, physicochemical parameters, δ¹³C_DIC value and two common approaches(floating chamber(FC) and thin boundary layer models(TBL) were used to analyze the CO₂ degassing characteristics in Guijiang River, a karst river, China. The results were as follows:1 Hydrochemistry in Guijiang River basin showed a significant spatial change. All of HCO₃^-, Ca²⁺, specific conductivity, total dissolved solids(TDS), SIc and pCO₂ showed similar distribution characteristics in the following order:tributaries in the middle reaches > middle reaches > Downstream > Upstream of Guijiang River. 2 During the monitoring period, CO₂ degassing occurred in all the sampling sites and it was the CO₂ source for the atmosphere. The mean CO₂ evasion was 237 mg·(m²·h)^-1 in Guijiang River, which located in the range of average CO₂ evasion of global river. However, significant spatial variations also occurred along Guijiang River. The CO₂ degassing flux in tributaries of the middle reaches and middle reaches of the mainstream were obviously larger than those in downstream and upstream of the mainstream. 3 CO₂ degassing was mainly affected by carbonate equilibrium system in tributaries in the middle reaches and middle reaches in the mainstream of the Guijiang River basin, which resulted in obviously larger CO₂ degassing than those in downstream and upstream of mainstream. However, the CO₂ degassing flux in tributaries of the middle reaches was also simultaneously affected by biological photosynthesis, and the minimum CO₂ degassing flux[6.38 mg·(m²·h)^-1] appeared in tributaries of the middle reaches. In addition, the CO₂ degassing flux in mainstream upstream was mainly affected by atmospheric environmental factors, while it was synergetically influenced by many factors in mainstream downstream.