Spatial and seasonal variability of CO_2 flux at the air-water interface of the Three Gorges Reservoir

Diffusive carbon dioxide （CO2） emissions from the water surface of the Three Gorges Reservoir, currently the largest hydroelectric reservoir in the world, were measured using floating static chambers over the course of a yearlong survey. The results showed that the average,annual CO2 flux was （163.3 ± 117.4） mg CO2/（m^2.hr） at the reservoir surface, which was larger than the CO2 flux in most boreal and temperate reservoirs but lower than that in tropical reservoirs. Significant spatial variations in CO2 flux were observed at four measured sites, with the largest flux measured at Wushan （221.9 mg CO2/（m^2.hr）） and the smallest flux measured at Zigui （88.6 mg CO2/（m^2.hr））; these differences were probably related to the average water velocities at different sites. Seasonal variations in CO2 flux were also observed at four sites, starting to increase in January, continuously rising until peaking in the summer （June-August） and gradually decreasing thereafter. Seasonal variations in CO2 flux could reflect seasonal dynamics in pH, water velocity, and temperature. Since the spatial and temporal variations in CO2 flux were significant and dependent on multiple physical, chemical, and hydrological factors, it is suggested that long-term measurements should be made on a large spatial scale to assess the climatic influence of hydropower in China, as well as the rest of the world.