Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge

Hongbing Tan; Xi Chen; Dongping Shi; Wenbo Rao; Jing Liu; Jintao Liu; Christopher J Eastoe; Jiarong Wang

doi:10.1016/j.scitotenv.2020.143510

Base flow in the Yarlungzangbo River, Tibet, maintained by the isotopically-depleted precipitation and groundwater discharge

Sci Total Environ. 2021 Mar 10:759:143510. doi: 10.1016/j.scitotenv.2020.143510. Epub 2020 Nov 12.

Authors

Hongbing Tan¹, Xi Chen², Dongping Shi³, Wenbo Rao³, Jing Liu⁴, Jintao Liu⁵, Christopher J Eastoe⁶, Jiarong Wang⁵

Affiliations

¹ School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China. Electronic address: tan815@sina.com.
² Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China. Electronic address: xichen@hhu.edu.cn.
³ School of Earth Sciences and Engineering, Hohai University, Nanjing 210098, China.
⁴ Institute of Surface-Earth System Science, Tianjin University, Tianjin 300072, China.
⁵ College of Hydrology and Water Resources, Hohai University, Nanjing 210098, China.
⁶ Department of Geosciences, University of Arizona, Tucson, AZ 85721, United States.

PMID: 33221005
DOI: 10.1016/j.scitotenv.2020.143510

Abstract

The extension-induced rift systems on the Tibetan Plateau (TP) may convey large amount of groundwater to rivers, but sources and flow paths of such groundwater are unknown. The Yarlungzangbo River (YR) is the only large river that traverses the southern Tibetan plateau from west to east, following one major suture zone that is cut by extensional normal faults. The faults could influence the flow paths of groundwater discharging to the river. In this study, O and H isotopes, major ions and ²²²Rn concentrations are analyzed along the YR, and interpreted in relation to structural geology and tectonics. The YR exhibits an abrupt change of isotopic and chemical compositions along with a large increase in flow where the middle reach intersects NE-SW-trending rifts. Low values of δD and δ¹⁸O and high concentrations of major ions and ²²²Rn in the middle reach show that waters are modified isotopically and chemically by a variety of possible water origins, such as recharge of high-altitude glacier melt and discharge from groundwater. Groundwater contributes 27 to 40% of the river flow in the middle reach. Isotopically-light meltwater from high-altitude glacier melt cannot account for the isotope composition of the present outflow of groundwater. The O and H isotope data in the YR and discharging groundwater can be well explained by the groundwater originated as paleo-precipitation during a cooler time, such as the late Pleistocene to early Holocene. The paleo-groundwater discharge can account for about 36 × 10⁸ m³ water budget unbalance in the middle reach. The study provides the first clear isotope evidence for the source of groundwater discharge into a large river through favorable conduits in large-scale active tensile fault zones and confirms the regional scale of groundwater flow on the Tibetan Plateau. Understanding the characteristics and changes of streamflow and surface-groundwater circulation on the Tibetan Plateau will help to manage water resources under a changing environment.

Keywords: Base flow; Groundwater; Isotopes; Tensile faults; Tibet; Yarlungzangbo River.