Hydrogen and Oxygen Isotopes in Yangtze River Water and Its Application in Tracing Basin-Scale Water Cycle

Abstract:

This paper reports the temporal and spatial variations of the hydrogen （δD） and oxygen （δ¹⁸O） isotopes in the mainstream of the Yangtze River and discusses the basin-scale surface water cycle， with the samples from six sampling campaigns along the mainstream and major tributaries of the Yangtze River from 2012 to 2015 and from three-year sampling at Nantong Station. Combined with multi-year isotope data， it estimates the multi-year average river water line of the mainstream of the Yangtze River as δD＝7.56 δ¹⁸O＋6.75， n＝333， r²＝0.939 9， p<0.000 1. The spatial variation of the isotopic composition in the mainstream of the Yangtze River is jointly affected by water sources， evaporation， and human activities， and indicates the integrated influence of continental effect， latitude effect and altitude effect. The seasonal variation of the isotopes in the lower mainstream is mainly controlled by monsoon precipitation， while the inter-month variation is mainly affected by the impoundment of the Three Gorges Dam and the contribution of the two lakes downstream the dam. Especially during the peak flood period， the river water isotope is abnormally enriched， reflecting the significant discharge from the lakes， paddy field water， and groundwater in the middle and lower basins. The massive dam construction in the river basin has a significant impact on the river water retention， mixing and homogenization， and has significantly affected the water cycle in the Yangtze River catchment. Its impact on the river and coastal ecological environment is worthy of in-depth study.