Three Gorges Dam alters the Changjiang (Yangtze) river water cycle in the dry seasons: Evidence from H-O isotopes Kai Deng a,b , Shouye Yang b,c, ⁎, Ergang Lian a,b , Chao Li b , Chengfan Yang a,b , Hailun Wei a,b a School of Ocean and Earth Science, Tongji University, Shanghai, 200092, China b State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China c Laboratory for Marine Geology, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266061, China HIGHLIGHTS • Stable H-O isotopes indicate the Changjiang river water cycle in dry sea- sons. • The isotopic parameter “d-excess” re- veals the origins of surface water. • The TGD impoundment causes the iso- topic homogenization in the reservoir. • The water mixing determines small d- excess variations in the mid-lower mainstream. • The damming effect has buffered the natural variability of river water cycle. GRAPHICAL ABSTRACT abstract article info Article history: Received 28 November 2015 Received in revised form 29 March 2016 Accepted 29 March 2016 Available online xxxx Editor: D. Barcelo As the largest hydropower project in the world, the Three Gorges Dam (TGD) has attracted great concerns in terms of its impact on the Changjiang (Yangtze) River and coastal marine environments. In this study, we measured or collected the H-O isotopic data of river water, groundwater and precipitation in the mid-lower Changjiang catchment during the dry seasons of recent years. The aim was to investigate the changes of river water cycle in response to the impoundment of the TGD. Isotopic evidences suggested that the mid-lower Changjiang river water was ultimately derived from precipitation, but dominated by the mixing of different water masses with variable sources and isotopic signals as well. The isotopic parameter “deuterium excess” (d-excess) yielded large fluctuations along the mid-lower mainstream during the initial stage of the TGD impoundment, which was inherited from the upstream water with inhomogeneous isotopic signals. However, as the reservoir water level rising to the present stage, small variability of d-excess was observed along the mid-lower main- stream. This discrepancy could be explained that the TGD impoundment had significantly altered the water cycle downstream the dam, with the rising water level increasing the residence time and enhancing the mixing of reservoir water derived from upstream. This eventually resulted in the homogenization of reservoir water, and thus small fluctuations of d-excess downstream the dam after the quasi-normal stage (2008 to present). We infer that the retention effect of large reservoirs has greatly buffered the d-excess natural variability of water cycle in Keywords: Changjiang (Yangtze) River Water cycle Three Gorges Dam Stable isotopes Deuterium excess Science of the Total Environment 562 (2016) 89–97 ⁎ Corresponding author at: State Key Laboratory of Marine Geology, Tongji University, Shanghai 200092, China. E-mail address: syyang@tongji.edu.cn (S. Yang). http://dx.doi.org/10.1016/j.scitotenv.2016.03.213 0048-9697/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv