Abstract:

The background value of methane (CH4) concentration was measured in 2010 at 05 m above the wateratmosphere interface and the bank of the Three Gorges Reservoir (TGR).CH4 fluxes from the TGR were determined by the static floating chamber and gas chromatography analysis methods.The results showed that the annual average of CH4 concentration was 2216±0224 mL/m3 at 05m above the wateratmosphere interface and 2211±0206 mL/m3 at the bank of the TGR,and the difference between them was not significant.Seasonal variations of CH4 concentrations were very small.CH4 concentrations were up to 2850 mL/m3 at the wateratmosphere interface of Yunyang in summer.But in the other sites,seasonal average CH4 concentrations varied small and were close to the annual average value.There were apparently spatial variations in CH4 concentration at 05 m above the reservoir surface.The CH4 concentration gradually decreased from Yunyang (231±033 mL/m3),Wushan (220±018 mL/m3) to Zigui (214±013 mL/m3) with the distance from the Three Gorges Dam (TGD).Furthermore,the CH4 concentration in the river downstream of the TGD (Sandouping:221±016 mL/m3) was higher than that in the upstream of the TGD (Zigui:214±013 mL/m3),but there was no significant difference between the two sites.The annual average CH4 fluxes of three sites from the upstream to the downstream in the TGR were 0454,0260 and 0115 mg/(m2·h),respectively,and the average CH4 flux in the downstream dam site (Sandouping) was also higher than that in the upstream dam site (Zigui).The spatial pattern of CH4 concentrations in the TGR was the similar with that of CH4 emission fluxes,which showed that CH4 fluxes were a crucial factor causing the difference of the CH4 concentrations in the TGR.