Abstract
When groundwater represents most of the world’s reserves of unfrozen freshwaters, water quality is commonly a limiting factor in quantifying usable fresh groundwater storage, especially in arid and semi-arid areas. Tracing the origin of major ions is important to the understanding of hydrochemical evolution and water–rock interaction. Strontium (Sr) and calcium (Ca) are geochemically similar in terms of ionic radius and ionic charge and can substitute for each other in mineral lattices such as in carbonates and silicates. This allows the use of Sr as a proxy for Ca during water–rock interaction. Geochemical mass balance and carbon and strontium isotope techniques were employed to study the origin of each major ion (such as Na, Ca, Mg, Cl, and SO4) in a loess aquifer (there is 10% to 20% of carbonate in the loess). Geochemical mass balance between atmospheric deposition and groundwater shows that the Cl (average concentration of 5.5 mg/L) and SO4 (average concentration of 6.8 mg/L) in groundwater originated from atmospheric deposition. The dissolution of loess using acetic acid was used to analyze the 87Sr/86Sr ratio of carbonate (mainly deposited in continental environments). Groundwater 87Sr/86Sr ratios (0.710677 to 0.712319) are consistent with 87Sr/86Sr ratios in carbonate (0.710329 to 0.711085) but are significantly lower than the whole-rock (0.715136 to 0.717155) and residue (0.719091 to 0.720438), suggesting that Ca and Mg mainly originated from the dissolution of carbonate in the loess aquifer. However, Na originated from the dissolution of albite, suggesting saturation controls the ability of dissolution. There are cation exchanges between Ca + Mg and Na, resulting in Na concentration increases and Ca + Mg concentration decreases in groundwater. This study is important to the understand of the origin of the major ions in groundwater and the geochemical processes in silicate-carbonate aquifers.
Highlights
Groundwater represents about 96% of the world’s reserves of unfrozen freshwaters [1].Groundwater is of fundamental significance for human development to meet the rapidly expanding urban, industrial, and agricultural water requirements, especially in arid and semi-arid areas [2], and more than two billion people in the world depend on groundwater for their daily supply [3].water quality is a limiting factor for usable fresh groundwater utilization [4,5]
This study is important to the understand of the origin of the major ions in groundwater and the geochemical processes in silicate-carbonate aquifers
This study aims to determine the origin of the major ions in the Xifeng loess aquifer, in NW China, mainly using major ion chemistry and C
Summary
Groundwater represents about 96% of the world’s reserves of unfrozen freshwaters [1].Groundwater is of fundamental significance for human development to meet the rapidly expanding urban, industrial, and agricultural water requirements, especially in arid and semi-arid areas [2], and more than two billion people in the world depend on groundwater for their daily supply [3].water quality is a limiting factor for usable fresh groundwater utilization [4,5]. Groundwater represents about 96% of the world’s reserves of unfrozen freshwaters [1]. Groundwater is of fundamental significance for human development to meet the rapidly expanding urban, industrial, and agricultural water requirements, especially in arid and semi-arid areas [2], and more than two billion people in the world depend on groundwater for their daily supply [3]. Water quality is a limiting factor for usable fresh groundwater utilization [4,5]. Poor water quality can be caused by a natural condition (such as strong aridity or many soluble salts in an aquifer) and by human activities (such as fertilizer utilization and drainage of waste waters). The impact of human activities on water quality were only recognized in the past half-century before which time, pristine conditions reflecting natural processes controlled the hydrochemistry [6].
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