Greenhouse gas emissions from hydroelectric dams have recently given rise to controversies about whether hydropower still provides clean energy. China has a large number of dams used for energy supply and irrigation, but few studies have been carried out on aquatic nitrous oxide (N₂O) variation and its emissions in Chinese river-reservoir systems. In this study, N₂O spatiotemporal variations were investigated monthly in two reservoirs along the Wujiang River, Southwest China, and the emission fluxes of N₂O were estimated. N₂O production in the reservoirs tended to be dominated by nitrification, according to the correlation between N₂O and other parameters. N₂O saturation in the surface water of the Wujiangdu reservoir ranged from 214% to 662%, with an average fluctuation of 388%, while in the Hongjiadu reservoir, it ranged from 201% to 484%, with an average fluctuation of 312%. The dissolved N₂O in both reservoirs was over-saturated with respect to atmospheric equilibrium levels, suggesting that the reservoirs were net sources of N₂O emissions to the atmosphere. The averaged N₂O emission flux in the Wujiangdu reservoir was 0.64 mu mol m(-2) h(-1), while it was 0.45 mu mol m(-2) h(-1) in the Hongjiadu reservoir, indicating that these two reservoirs had moderate N₂O emission fluxes as compared to other lakes in the world. Downstream water of the dams had quite high levels of N₂O saturation, and the estimated annual N₂O emissions from hydropower generation were 3.60 x 10(5) and 2.15 x 10(5) mol N₂O for the Wujiangdu and the Hongjiadu reservoir, respectively. These fluxes were similar to the total N₂O emissions from the reservoir surfaces, suggesting that water released from reservoirs would be another important way for N₂O to diffuse into the atmosphere. It can be concluded that dam construction significantly changes the water environment, especially in terms of nutrient status and physicochemical conditions, which have obvious influences on the N₂O spatiotemporal variations and emissions. (C) 2011 Elsevier Ltd. All rights reserved.

Publication name	ATMOSPHERIC ENVIRONMENT　Volume: 45 　Issue: 31 　Pages: 5458-5468　Published: OCT 2011
Author(s)	Liu, Xiao-Long; Liu, Cong-Qiang; Li, Si-Liang; Wang, Fu-Shun; Wang, Bao-Li; Wang, Zhong-Liang
Corresponding author	LIU Xiaolong  liuxiaolong@inbox.com, liucongqiang@vip.skleg.cn  1. Tianjin Normal Univ, Tianjin Key Lab Water Resources & Environm, Tianjin 300387, Peoples R China  2. Chinese Acad Sci, Inst Geochem, State Key Lab Environm Geochem, Guiyang 550002, Peoples R China

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