Abstract
Major ions and selected environmental tracers (D, 18O, 3H and chlorofluorocarbons (CFCs)) were employed to determine the source, flow rates, and hydrochemical evolution of groundwater in an alluvial fan along the front of the Qilian Mountains, which serves as an important groundwater reservoir in northwest China. Temporal and spatial variations in ion concentrations were limited near the upper portion of the alluvial fan. However, groundwater quality deteriorated along the flow path as concentrations of Mg2+, Na+, SO42−, and Cl− increased toward the fan toe and into the center of the valley. The relative abundance of the major cations and anions also changed down-fan from Ca2+ to Na+ and Mg2+, and from HCO3− to SO42− and Cl−, respectively. Isotopic data suggests that precipitation within the Qilian Mountains, which recharged the alluvial deposits near the mountain front, was the primary source of groundwater. Apparent groundwater ages determined by CFCs varied from 23 to 40 years, and in general, increased in age from south to north (down-fan). It is concluded that groundwater in the study area was recharged by the Qilian Mountains, flowed through the alluvial fan from south to north, and was subsequently discharged several decades later from springs located along the toe of the fan, after which it re-entered the Shule River.
Highlights
Shortages in water resources represent a serious problem in many areas of the planet within semi-arid and arid regions [1,2]
The total measured dissolved in solids (TDS), pH, electronic conductivity, temperature and major ion concentrations the groundwater samples are shown in Table
Electrical conductivity concentrations measured in the groundwater samples are shown in
Summary
Shortages in water resources represent a serious problem in many areas of the planet within semi-arid and arid regions [1,2]. Many investigators have combined hydrogeochemical methods with isotopic and geochemical tracer techniques to determine the source of the groundwater, its rate of migration, its age and residence time, and its geochemical evolution along the subsurface flow path [28,29,30] An understanding of these parameters is vital for the effective management of groundwater resource. A host of studies have been conducted in arid areas of northwestern China to characterize the region’s groundwater and to more effectively utilize its limited water resources The majority of these analyses have focused on the Zhangye, Ejina, Minqin, and Dunhuang Basins [1,2,7,13,31,32,33]. A large amount water infiltrates intosprings the gravel of discharged from located fine-grained soil within the of adjacent plain These later the Changma alluvial fan to recharge the groundwater system. May to September (data from the Hydrological Bureau in Lanzhou of Gansu province, China)
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