Variation and Influencing Factors of CO2 Flux at the Water-Air Interface of Dammed Rivers in Karst Mountainous Areas
Reservoirs are an important component of inland water ecosystems and play an important role in regulating regional and glob-al carbon cycles.In order to understand the variation and influencing factors of CO2 diffusion fluxes at the water-air interface of dammed rivers in karst mountainous areas,we systematically monitored the physicochemical parameters of the water column in Pingzhai Reser-voir within Guizhou Province Qianzhong Water Conservancy Shuniu Project in January,May,July and November 2020,and calculated the CO2 diffusion fluxes at the water-air interface using the TBL model.The results reveal that the water chemistry of Pingzhai reservoir is of HCO3+SO4-Ca type and is mainly controlled by carbonate weathering.The variation in pCO2 and CO2 diffusion fluxes in surface water ranged from 124.64 to 558.76 μatm and from-18.85 to 15.90 mg/(m2·d).The surface water served as a source of atmos-pheric CO2 in January and as a sink of atmospheric CO2 in May,July and November.The value of pCO2 along the water column was low in the surface layer and high in the bottom,ranging from 124.64 to 5 409 μatm.The factors affecting the CO2 diffusion flux at the water-air interface in Pingzhai Reservoir are mainly(1)the changes of pCO2 along the water column caused by the carbonate equilibri-um shift,altering subsequently the carbon speciation in water,(2)suppression of CO2 diffusion into the atmosphere via the uptake of carbon compounds by phytoplankton for photosynthesis and(3)the temporary CO2 sequestration during the thermal stratification period and the overlying degassing during the mixing period in the bottom waters.
CO2 diffusion fluxchange featuresinfluence factorkarst reservoir
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