AUTHOR=Yan Ya-Ni , Zhang Jun-Wen , Zhang Wei , Zhang Gui-Shan , Guo Jian-Yang , Zhang Dong , Wu Jie , Zhao Zhi-Qi TITLE=Spatiotemporal Variation of Hydrogen and Oxygen Stable Isotopes in the Yarlung Tsangpo River Basin, Southern Tibetan Plateau JOURNAL=Frontiers in Earth Science VOLUME=9 YEAR=2021 URL=https://www.frontiersin.org/journals/earth-science/articles/10.3389/feart.2021.757094 DOI=10.3389/feart.2021.757094 ISSN=2296-6463 ABSTRACT=

Characterization of spatiotemporal variation of the stable isotopes δ¹⁸O and δD in surface water is essential to trace the water cycle, indicate moisture sources, and reconstruct paleoaltimetry. In this study, river water, rainwater, and groundwater samples were collected in the Yarlung Tsangpo River (YTR) Basin before (BM) and after the monsoon precipitation (AM) to investigate the δ¹⁸O and δD spatiotemporal variation of natural water. Most of the river waters are distributed along GMWL and the line of d-excess = 10‰, indicating that they are mainly originated from precipitation. Temporally, the δ¹⁸O and δD of river water are higher in BM series (SWL: δD = 10.26δ¹⁸O+43.01, R² = 0.98) than AM series (SWL: δD = 9.10δ¹⁸O + 26.73, R² = 0.82). Spatially, the isotopic compositions of tributaries increase gradually from west to east (BM: δ¹⁸O = 0.65Lon (°)-73.89, R² = 0.79; AM: δ¹⁸O = 0.45Lon (°)-57.81, R² = 0.70) and from high altitude to low (BM: δ¹⁸O = −0.0025Alt(m)-73.89, R² = 0.66; AM: δ¹⁸O = −0.0018Alt(m)-10.57, R² = 0.58), which conforms to the “continent effect” and “altitude effect” of precipitation. In the lower reaches of the mainstream, rainwater is the main source, so the variations of δ¹⁸O and δD are normally elevated with the flow direction. Anomalously, in the middle reaches, the δ¹⁸O_mainstream and δD_mainstream values firstly increase and then decrease. From the Saga to Lhaze section, the higher positive values of δ¹⁸O_mainstream are mainly caused by groundwater afflux, which has high δ¹⁸O and low d-excess values. The δ¹⁸O_mainstream decrease from the Lhaze to Qushui section is attributed to the combined action of the import of depleted ¹⁸O and D groundwater and tributaries. Therefore, because of the recharge of groundwater with markedly different δ¹⁸O and δD values, the mainstream no longer simply inherits the isotopic composition from precipitation. These results suggest that in the YTR Basin, if the δ¹⁸O value of surface water is used to trace moisture sources or reconstruct the paleoaltimetry, it is necessary to rule out the influence from groundwater.