When hydropower rose, hydroelectricity was portrayed as a renewable energy without any carbon emission. The recognition in carbon sinks/sources of reservoirs has experienced 4 phases by far. Hydropower is encouraged to develop in China to realize their goal of “carbon peak in 2030, carbon neutrality in 2060.” Several giant hydroelectric plant stations, such as Xiluodu, Baihetan, Xiangjiaba, Wudongde, have been finished in the Mekong River in the southwest of China recently, promoting the proportion of hydropower in Chinese energy structure ( Li Z.
What is the carbon footprint of hydroelectric reservoirs, carbon-neutral energy, carbon sinks, or carbon sources ( Prairie et al., 2018)? It is vital for policy makers to choose suitable national strategies to develop hydropower at the background of reducing carbon emission nowadays. Therefore, CO 2 emission from the drained soils should be included in the carbon budget of reservoir systems, especially for these reservoirs with a large drawdown area. CO 2 emission from the TGR drawdown area was estimated to be 342.67–495.96 Gg yr −1 in the drained season, and offset about 80% of carbon fixation by vegetation in the TGR drawdown area. CO 2 emission flux in the drained season was positively correlated with air temperature, soil temperature at 5 cm depth, soil water content, organic carbon, and soil nitrate nitrogen, but negatively correlated with elevations. The average CO 2 emission flux in the drained season was about 1.7 times higher than that in the inundated season in our experiments, and the ratio increased to 4.8 times when other available data was added. Both the diel and seasonal variation indicated that CO 2 emission fluxes were significantly higher in the drained season than in the flooded season. To demonstrate the contribution of CO 2 emissions from the TGR drawdown areas, the study measured CO 2 emissions from the downstream part of the TGR drawdown areas by the chamber method, and synthesized CO 2 emissions from the other parts of TGR drawdown areas. However, the total CO 2 emissions from the TGR drawdown area have seldom been estimated by far. Three Gorges Reservoir (TGR) has a large drawdown area, which accounts for nearly one third of the total area of the TGR. 2Zhejiang Academy of Forestry, Hangzhou, ChinaĪ huge amount of CO 2 emissions from the drained drawdown areas of reservoirs overturns the previous results in carbon budget.1Key Laboratory for Technology in Rural Water Management of Zhejiang Province, Zhejiang University of Water Resources and Electric Power, Hangzhou, China.Le Yang 1, Hao Lu 1, Xuefang Yu 1 and Hepeng Li 2*
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