Damming effect on the Changjiang (Yangtze River) river water cycle based on stable hydrogen and oxygen isotopic records

• The effect of Three Gorges Dam on the Changjiang river water cycle is investigated based on H–O isotopes.
• The δ18O anomaly pattern change indicates one month slowdown of river water cycle before and after the dam construction.
• This time lag is a result of trapping effect and water regulation of reservoirs due to the Three Gorges Dam.

More than 50,000 dams have been built in the Changjiang (Yangtze River) catchment over the last half century, among which the Three Gorges Dam (TGD) is the largest hydroelectric engineering project in the world. The trapping effect of the TGD on the decline of Changjiang sediment flux has been widely documented, while the damming impact on river water cycle has not received enough attention because of the relative consistence of annual water discharge. In this regard, we present a new isotopic evidence to illustrate the damming effect on the Changjiang river water cycle based on stable hydrogen and oxygen isotopes. A historical comparison of seasonal distribution of stable oxygen isotope in the Changjiang river water indicates that the time lag of river water response to meteoric precipitation has changed from one month in the early 1980s to approximately two months in the past decade. The one-month slowdown of Changjiang river water cycle is probably the result of increasing trapping and water regulation effect by numerous dams in the catchment. This study provides the first quantitative evaluation of this significant damming impact on the Changjiang river water cycle, and the damming effects on ecosystem and biogeochemical process in river and marginal sea, as well as on socioeconomic development in China, have to be carefully considered in the future.