Assessing the Influences of Land Use Change on Groundwater Hydrochemistry in an Oasis-Desert Region of Central Asia

Wanrui Wang,Shuai Zhang,Yuhai Yang,Ziyang Zhu,Weihua Wang,Yapeng Chen,Yifeng Hou

doi:10.3390/w14040651

Abstract

Land use change greatly affects groundwater hydrochemical cycling and thereby food and ecosystem security in arid regions. Spatiotemporal distribution of groundwater hydrochemistry is vital to understand groundwater water-salt migration processes in the context of land use change, while it is not well known in the oasis-desert region of arid inland basins. Here, to investigate the influences of land use change on groundwater hydrochemistry and suggest sustainable management, 67 water samples were obtained in the Luntai Oasis, a typical oasis desert of Central Asia. Stable isotopes and chemical components of samples were analyzed. Piper and Gibbs plots were used to elaborate the chemical type and major mechanisms controlling water chemistry, respectively. The results showed that cultivated land area has markedly expanded in the Luntai Oasis over the last 20 years (increasing by 121.8%). Groundwater seasonal dynamics and groundwater–surface water interaction were altered dramatically by farmland expansion and groundwater exploitation. Specifically, the spatial heterogeneity and seasonal variability of groundwater hydrochemistry were significant. Compared with the desert area, the δ18O and TDS of river water and shallow groundwater in the oasis cropland exhibited lower values but greater seasonal variation. Higher TDS was observed in autumn for river water, and in spring for shallow groundwater. The chemical evolution of phreatic water was mainly controlled by the evaporation-crystallization process and rock dominance, with a chemical type of Cl-SO4-Na-Mg. Significant spatiotemporal heterogeneity of groundwater hydrochemistry demonstrated the influence of climatic, hydrogeological, land use, and anthropogenic conditions. Groundwater overexploitation would cause phreatic water leakage into confined water, promoting groundwater quality deterioration due to fresh saltwater mixing. Improving agricultural drainage ditches in conjunction with restricting farmland expansion and groundwater extraction is an effective way to alleviate groundwater environment deterioration and maintain oasis-desert ecosystems in arid regions.

Highlights

Groundwater is crucial for eco-environmental protection and economic development in arid regions due to limited surface water, especially in arid inland regions [1,2,3]
The spatiotemporal distribution of groundwater hydrochemistry and its responses to land use change were examined using data of 67 water samples obtained in an oasis-desert region of the Tarim Basin
A higher TDS was observed in autumn for river water, while in spring for shallow groundwater

Summary

Introduction

Groundwater is crucial for eco-environmental protection and economic development in arid regions due to limited surface water, especially in arid inland regions [1,2,3]. Human intervention (e.g., land use change and irrigation) has caused groundwater depletion and aquifer salinization in arid and semi-arid areas, challenging the local water-food-ecological security [7,8,9,10,11]. The expansion of cultivated areas is necessary to satisfy the food requirements of a growing population, resulting in a markedly increasing irrigation water demand for agriculture development thanks to well-developed irrigation canal systems [3,11,12]. Groundwater hydrochemistry is crucial for biogeochemical cycling because it could impact water utilization and the ecological function of groundwater [15,16]. A deep understanding of groundwater hydrochemistry and groundwater–surface water interactions impacted by land use change is essential for effective groundwater management for ecological and human requirements in oasis-desert regions [17]

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Discussion

Conclusion