Spatial and seasonal variability of CO2 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/(m²hr) 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/(m²hr)) and the smallest flux measured at Zigui (88.6 mg CO₂/(m²hr)); 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.