Delineation of groundwater flow and estimation of lake water flushing time using radium isotopes and geochemistry in an arid desert: The case of Badain Jaran Desert in western inner Mongolia (CHN)

doi:10.1016/j.apgeochem.2020.104740

Applied Geochemistry

Volume 122, November 2020, 104740

https://doi.org/10.1016/j.apgeochem.2020.104740 Get rights and content

Highlights

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Ra mass balance equations were developed and their practicability in arid lake’s hydrology was verified.
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The groundwaters of the southern and northern parts of Badain Jaran Desert likely belong to different systems.
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The flushing times of these lakes were estimated to be 0.05-9.23 yrs.

Abstract

The Badain Jaran Desert, located in western Inner Mongolia in northwestern China, is characterized by the coexistence of high megadunes and numerous lakes. The spatial distribution of groundwater systems and supply sources of lakes have yet to be elucidated. Ra isotopes and geochemistry of water samples from 17 lakes and their peripheral groundwater were investigated. The characteristics of the geochemical behaviors of Ra isotopes, including activities, activity ratios, main sources and sinks, and geochemistry both of groundwater and lake water, suggest that there are two groundwater flow systems in the studied area: the southern-central and the northern groundwater flow systems. The southern-central groundwater is supplied from mountains farther to the south and the northern groundwater supplied from areas farther to the north. We developed mass balance models for ²²⁸Ra in fresh and saline lakes. The equation for the saline lakes has three input terms: groundwater discharge, atmospheric deposition and diffusion from bottom sediments; and two outputs: radioactive decay and coprecipitation. The freshwater lake equation has one input term: radionuclide supply from groundwater; and two output terms: adsorption onto particles in the lake and radioactive decay. Mass balance calculations for ²²⁸Ra give discharge fluxes of 0.03 × 10⁶–7.72 × 10⁷ m³ yr⁻¹ for the lakes. The flushing times of the lakes were estimated to be 0.05–9.23 yrs. The results of this study promote scientific understanding of the hydrologic cycle and water resource evaluation in the Badain Jaran Desert and provide a paradigm for radium isotope application in hydrological research in arid areas.

Introduction

The Badain Jaran Desert, located in the western Inner Mongolia area of China, is well known for its distribution of numerous megadunes and lakes. Since the 1930s, research on the Badain Jaran Desert has been primarily concerned with the formation mechanism of megadunes and associated with the source of recharge for the interdune lakes; however, there has been much controversy (Lou, 1962; Yang and Scuderi, 2009; Yang et al., 2010). Along with low soil fertility and extreme climate, freshwater scarcity is a limiting factor for agricultural and economic development in this region. The source of the groundwater recharging these desert lakes has been an object of research since the 1970s (Wang and Zhou, 2018). An understanding of the source of groundwater in the Badain Jaran Desert is significant not only to policy makers for regional planning but also to scientists interested in hydrological cycles in arid environments and climate change in northern China and other arid regions of Asia (Yang et al., 2010; Gates et al., 2008a). Past research proposed various opinions concerned with the primary sources of groundwater and lake water in this arid desert, including from local precipitation (Dong et al., 2009; Yang et al., 2010), from paleowaters in the Last Glacial Maximum (Edmunds and Wright, 1979; Ma and Edmunds, 2006), from the peripheral rivers and alluvium and diluvium groundwater of the desert (Ding and Wang, 2007; Liu, 2010), and even farther from the Qinghai-Tibet Plateau (Chen et al., 2004).

Comparing the outer sources of the groundwater and lake water, hydraulic connections of groundwater and the flushing time of lakes is another important aspect of evaluating water resources within this arid desert basin. To date, there are few studies that have investigated groundwater flow system delineation and the flushing time of lakes within this desert basin. However, groundwater abstraction is increasing in nearby areas, and the need for easily accessible freshwater could extend pumping to the desert or hydraulically connected areas, potentially threatening livelihoods and a unique oasis ecosystem that is dependent upon groundwater (Gates et al., 2008b).

The naturally occurring Ra quartet with a wide range of half-lives (²²⁶Ra, T_1/2 = 1600 yr; ²²⁸Ra, T_1/2 = 5.7 yr; ²²³Ra, T_1/2 = 11.1 d;²²⁴Ra, T_1/2 = 3.64 d) is found to some extent in all natural waters and has been shown to be an ideal tracer of hydrogeological processes on coastal waters (Moore and Shaw, 2008), lakes (Kraemer, 2005) and rivers (Eikenberg et al., 2001) on the time scale of a few days to thousands of years. However, due to its reactivity and nonconservative behavior, Ra is rarely used for tracing groundwater seepage into fresh or hypersaline surface water. In freshwater, Ra is lost mostly through adsorption onto sediments and suspended particles. In hypersaline environments Ra can be removed through coprecipitation, most notably with sulfate salts (Raanan, 2011). The hydrochemical characteristics of the Badain Jaran Desert represent a combination of underground freshwater with hypersaline lakes. The lakes and groundwater of the Badain Jaran Desert provide the opportunity to gain a comprehensive dataset of the radium isotopes of an arid environment with a large salinity range and different groundwater paths.

The aims of this study are to present a relatively realistic delineation of the groundwater flow system and provide an estimation of the flushing time of lakes within the Badain Jaran Desert. In the process of research, first, we investigated radium isotopic compositions and major ions of groundwater and lake water in the Badain Jaran Desert. The groundwater system delineation was explored by analyzing the geochemical behavior of Ra isotopes in groundwater and lakes, including the relationship between Ra activities/activity ratios, the water chemistry parameters of groundwater. Then, the primary sources and sinks of Ra in lake water with different salinities were discussed. Subsequently, the Ra mass balance equations for the lake water were established. Finally, discharge flux and the flushing times of 17 lakes were estimated. The scientific significance of this study is to advance the understanding of the Badain Jaran Desert hydrological cycle, and the importance of this study in methodology is to demonstrate that radium isotopes can serve as a tool for hydrological cycle research.

Section snippets

Setting

The Badain Jaran Desert (39′20″N to 41′30″N; 100′1″ to 104′E) is situated on the Alxa Plateau in western Inner Mongolia with an area of approximately 44,000 km² (Fig. 1). In the S and SE, the desert is surrounded by the mountain ranges of ZongNai Shan, Mount Yabrai, Longshou Shan and Beida Shan, and in the W and N parts, it stretches down to the low and flat areas of the Gurinai grasslands and the Guezi Hu wetlands (Hofmann, 1996). The altitude of the area changes between 1600 m in the

Chemical composition of groundwater and lake water

Chemical parameters and major ion concentrations are presented in Appendix A. The most striking geochemical feature of the studied samples is a sharp difference in salinity between lake water and groundwater samples. As Fig. 2 shows, among the 17 lake water samples, three (SBJL, BDE and BETLG) located at the southern edge of the Badain Jaran Desert are freshwater, with TDS ranging from 1095 mg/L to 3069 mg/L. Three hyposaline lakes (SYWS, ENET and NHZ) located in the southern-central research

The differentiation of radium isotope activities and ratios

The sources of radium isotopes in groundwater are alpha recoil caused by the decay of the parent nuclide in the solid, desorption from the solid surface, dissolution of aquifer solids and in situ production by the decay of the dissolved parent nuclide. Sinks of radium in groundwater may include coprecipitation with sulfate minerals, adsorption and decay (Krishnaswami et al., 1982). These processes have different time scales, and the effect of each of them on radium activities in the groundwater

Conclusions

The analyses of lakes with a wide range of salinity and groundwater flow interactions with different aquifer rock types provide new insights into the behavior of radium isotopes in the hydrologic cycle of the Badain Jaran Desert. Radium isotopes and geochemical data may be used to characterize a groundwater flow system and mass balance in lakes. The main results obtained in this study can be summarized as follows: (1) Geochemistry, radium isotope activity and ratios of groundwater show spatial

Funding

This study was supported by National Key Research and Development Program of China (2016YFC0401404), the the State Key Laboratory of Cryospheric Sciences (SKLCS-OP-2019-10); Geological survey project of China Geological Survey(No.12120114018501).

Declaration of competing interest

The authors declare the following financial interests/personal relationships which may be considered as potential competing interests:

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Delineation of groundwater flow and estimation of lake water flushing time using radium isotopes and geochemistry in an arid desert: The case of Badain Jaran Desert in western inner Mongolia (CHN)

Highlights

Abstract

Introduction

Section snippets

Setting

Chemical composition of groundwater and lake water

The differentiation of radium isotope activities and ratios

Conclusions

Funding

Declaration of competing interest

Carsol. Sin./Zhong Guo Yan Rong

Appl. Geochem.

Geomorphology

J. Hydrol.

J. Environ. Radioact.

Appl. Geochem.

Mar. Chem.

Geochem. Cosmochim. Acta

Geochim.Cosmochim. Acta

Chem. Geol.

Water Resources Protection

Geochimica rt Cosmochimica Acta

Mar. Chem.

Mar. Chem.

Geochem. Cosmochim. Acta

Geochem. Cosmochim. Acta

Geochem. Cosmochim. Acta

Quat. Int.

Quat. Res.

Quat. Res.

Geochem. Cosmochim. Acta

Error-control and processes optimization of 223/224Ra measurement using delayed coincidence counter (RaDeCC)

J. Environ. Radioact.

Error-control and processes optimization of ^223/224Ra measurement using delayed coincidence counter (RaDeCC)