Comparative Study On The Air-water Fluxes Of CO₂ And CH₄ In The Three Gorges Reservoir And The Downstream Of Jinsha River,China

The study took the downstream of Jinsha River,the Yangtze mainstream and Pengxi River-a typical tributary in the Three Gorges Reservoir as the main research object.Through the optimization of headspace equilibrium measurement analysis method,analyzing the air-water CO2 and CH4 fluxes and its influencing factors of the downstream of Jinsha River in summer and winter.At the same time,a one-year monitoring of CH4 and CO2 fluxes was been making to analyze the characteristics in the Three Gorges Reservoir,illustrated the influencing factors of air-water CH4 and CO2 fluxes of different extents.This study obtained the following conclusions:(1)Results showed that there was a positive correlation between the CH4 fluxes and p(CH4),wind speed in summer.And the CO2 fluxes was mainly impacted by p(CO2),DIC,TA and wind speed in the downstream of Jinsha River.There was a positive correlation between the CH4 fluxes and p(CH4),wind speed and water temperature.And The CH4 fluxes was negatively correlated with Chl-a and TA.There was a positive correlation between the air-water CO2 fluxes and p(CO2)and wind speed,and it was also impacted by DO,Chl-a and DOC.The air-water CO2 fluxes was in medium level and the CH4 fluxes was low,comparing to other major rivers in the world.And the greenhouse effect was not obvious after the completion of the hydropower stations.(2)In May 2016 to February 2017,the CO2 and CH4 fluxes were on the decline after impoundment of the Three Gorges Reservoir.The CH4 fluxes was positively correlated with p(CH4)and water temperature,negatively correlated with conductivity and DO in the mainstream of the Three Gorges Reservoir.And the CO2 fluxes was positively correlated with p(CO2)and water temperature,negatively correlated with conductivity,DO and pH.The CH4 fluxes was positively correlated with p(CH4),water temperature and pH,and the CO2 fluxes was positively correlated with p(CO2)and wind speed,negatively correlated with DO,pH and Chl-a.Summary the mainstream and Pengxi River,the CH4 fluxes was positively correlated with p(CH4)and water temperature,negatively correlated with conductivity.And the CO2 fluxes was positively correlated with p(CO2),negatively correlated with DO and pH.The river area to the transition area of three gorges reservoir,the air-water CO2 diffusion fluxes reduced.It showed that the reservoir reduced the CO2 release.On the whole,the air-water CO2 fluxes of the mainstream river was greater than the Pengxi River.And the air-water CH4 fluxes of Pengxi River was greater than the mainstream river.The air-water CO2 fluxes of the Three Gorges Reservoir was higher than other rivers,and in medium level air-water,comparing to other major reservoirs in the world.The CH4 fluxes was low and it showed that the reservoir for emissions of CO2 and CH4 was not significant.(3)The CO2 fluxes of reservoir area in the downstream of Jinsha River area were greater than the Three Gorges Reservoir area in summer.And the CO2 fluxes of reservoir area in winter were lower than the summer.The CH4 fluxes of the Three Gorges Reservoir area were higher than the Jinsha reservoir area in summer and the CH4 fluxes were low in winter.The TC of the Jinsha river reservoir area was higher than the Three Gorges Reservoir area in summer,but the TC of the Three Gorges Reservoir was the higher after the impoundment.The reservoir age and the operation of the reservoir may affect the emissions of air-water CO2 and CH4 fluxes.