Origin of water in the Badain Jaran Desert, China: new insight from isotopes

Xu-Sheng Wang,Bill X. Hu,Yang Wang,Xiujie Wu

doi:10.5194/hess-21-4419-2017

Abstract

Abstract. To better understand the origin of water in the Badain Jaran Desert, China, water samples were collected from lakes, a spring and local unconfined aquifer for analyses of radiocarbon (14C), tritium (3H), stable hydrogen and oxygen isotope ratios (δ2H – δ18O), and d-excess values ( = δ2H – 8δ18O). A series of evaporation experiments were also conducted in the desert to examine how the isotopic signature of water may change during evaporation and infiltration under local environmental conditions. The results show that the lakes in the southeastern sand dune area are fed by groundwater discharging into the lakes and that local groundwater, on the other hand, is derived primarily from modern meteoric precipitation in the region. Although dissolved inorganic carbon (DIC) in groundwater yielded very old radiocarbon ages, the presence of detectable amounts of tritium in groundwater samples, together with their δ2H, δ18O and d-excess characteristics, strongly suggests that the old radiocarbon ages of DIC do not represent the residence time of water in the aquifer but are the result of addition of old DIC derived from dissolution of ancient carbonates in the aquifer. The data do not support the hypothesis that the water in the Badain Jaran Desert was sourced in remote mountains on the northern Tibetan Plateau. This study also finds no support for the hypothesis that present-day water resources in the desert were recharged by the precipitation that fell in the past during the early Holocene when the climate was much wetter than today. Instead, this study shows that both groundwater and lake water originated from meteoric precipitation in the region including mountainous areas adjacent to the desert under the modern climatic condition.

Highlights

Arid regions comprise nearly one-third of the Earth’s land area
The δD and δ18O values of the water samples collected from the pan evaporation experiments and evaporation–infiltration experiments are shown in Table 1 and Fig. 3
The isotopic patterns confirm the previous findings that groundwater supplies the lakes in the sand dunes area and the lake water is well mixed in the vertical direction

Summary

Introduction

Arid regions comprise nearly one-third of the Earth’s land area. In these regions, surface water and groundwater are scarce, due to the low precipitation and strong evaporation. Water isotopes have been widely used to identify water sources (e.g., Rademacher et al, 2002; Gates et al, 2008a; Morrissey et al, 2010; Chen et al, 2012), the isotopic composition of groundwater and surface water in arid environments can deviate significantly from that of local precipitation due to evaporation, which complicates the interpretation of water stable isotope data and can lead to equivocal inferences about recharge origin (e.g., Gates et al, 2008a, b; Chen et al, 2012). Despite the progress in the application of isotopes and other geochemical tracers in hydrological studies, the origin and residence time of groundwater in many arid and semi-arid areas remain open questions in water resource research

Methods

Results

Conclusion