Methane and nitrous oxide emissions from the drawdown areas of the Three Gorges Reservoir.

To investigate the effect of dam impounding on CH4 and N2 O emissions from the drawdown area of the Three Gorges Reservoir (TGR), CH4 and N2 O fluxes were measured at the elevations of 180 m, 175 m, 165 m and 155 m (above the sea level) from September 2010 to August 2012 using the static chamber technique. The elevations of 175 m, 165 m and 155 m were located in the drawdown area and the non-flooded elevation of 180 m was taken as the control for the drawdown area. The drawdown area studied here acted as the sources of CH4 and N2 O as a whole. Seasonal, inter-annual and spatial CH4 , but not N2 O, fluxes varied significantly between September 2010 and August 2012. The CH4 fluxes were highest in winter but lowest in summer, and significantly higher in the wet year than in the dry year. The annually cumulative CH4 emissions were 14.09 ± 4.27, 12.61 ± 3.59, 68.92 ± 13.09 and 77.41 ± 9.42 kg CH4  ha-1 from the elevations of 180 m, 175 m, 165 m and 155 m, respectively. Compared with 180 m elevation, the annual CH4 emission was insignificantly decreased by 11% at 175 m elevation (P > 0.05), and substantially increased by 389% and 449% at 165 m (P < 0.05) and 155 m elevations (P < 0.05), respectively. The annually cumulative N2 O emissions were 4.74 ± 1.78, 7.43 ± 2.57, 3.39 ± 1.05 and 8.83 ± 1.95 kg N2 O ha-1 from the above corresponding elevations, respectively, and there were no significant differences among the four elevations (P > 0.05). These results showed that CH4 emissions were increased but N2 O emissions were not affected in the drawdown area after the dam impounding in the TGR, and CH4 emissions were increased with the decrease in the elevations while N2 O emissions were not affected by the elevation in the drawdown area.