长江河水氢氧同位素组成示踪流域地表水循环

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

摘要:

基于2012-2015年开展的6次长江干、支流系统采样和南通站3个水文年的连续采样，通过氢氧同位素组成（δD和δ¹⁸O）分析，研究长江干流河水氢氧同位素时空变化特征及其对流域地表水循环的指示。结合多年同位素数据，长江干流多年平均河水线可以表示为：δD=7.56δ¹⁸O+6.75，n=333，R²=0.939 9，p＜0.000 1。长江干流河水同位素组成的空间变化受不同来源、蒸发作用以及人类活动的共同影响，并表现出大陆效应、纬度效应和海拔效应。下游河水同位素组成的季节性变化主要受控于季风降水，月际变化则主要受三峡大坝调蓄过程与下游两湖贡献比例的影响；尤其在洪峰事件中河水同位素异常偏正，反映中下游湖泊群、稻田水、地下水等显著贡献。流域大规模的大坝建设对河水的拦蓄和混合均一化作用，显著影响了长江流域水循环过程，其对河流和近海生态环境影响值得深入研究。

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.