CO2 and CH4 Fluxes Variation across Water-Air Interface and Influencing Fac-tors in Chongqing's Central Urban Area of the Three Gorges Reservoir During the Flood Season
The central urban section of Chongqing within the Three Gorges Reservoir is located in the fluctuating backwater area,which exhibits the dual characteristics of a natural river and a reservoir.However,the understanding of its greenhouse gas emis-sions remains insufficient.To investigate the changes of carbon dioxide(CO2)and methane(CH4)fluxes at the water-air interface,surface and bottom water samples were collected in Lijiatuo,Daxigou,Cuntan,Tangjiatuo and Guojiatuo in Chongqing's central urban area of the Three Gorges Reservoir in June and September 2020,respectively.The CO2 and CH4 fluxes at the water-air interface were calculated using the thin boundary layer(TBL)model estimation method.The sources and their contributions of particulate organic carbon(POC)were investigated using δ13C,N/C and isotope multiple mixed source analysis.The results show that the CO2 and CH4 fluxes at the water-air interface show"source"characteristics in the study area.The CO2 flux(1 880.25±366.75 μmol·m-2·h-1)in June were significantly higher than that in September(992.74±225.27 μmol·m-2·h-1),and the CH4 fluxes at the water-air interface were significantly higher in September(3.55±0.36 μmol·m-2·h-1)than that in June(2.26±0.59 μmol·m-2·h-1).In addition,the range of δ13C-POC variation in the aquatic system is from-24.27％o to-26.67％o,with no significant differences observed between months.The POC was mainly from the terrestrial sources(72±13)％,then from the autogenous sources(25±13)％.The main factors affecting the CO2 and CH4 fluxes at the water-air interface in this region were dissolved inorganic carbon(DIC)and particulate organic carbon(POC)in the water.In August 2020,the large influx of exogenous organic carbon(OC)from terrestrial sources became the main reason for the higher CH4 flux.
the Three Gorges Reservoirgreenhouse gaswater-air interface fluxstable isotopeinfluencing factors
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