Study on the hydrochemical characteristics of groundwater along the Taklimakan Desert Highway

Groundwater is the only water source of the shelterbelt along the Taklimakan Desert Highway in northwestern China. Understanding the hydrochemical zoning characteristics, material source, and hydrochemical processes of this desert groundwater is important for rational groundwater exploitation. Meanwhile, determining the location of the dividing boundary, which divides the influence ranges of the Tarim river and the Kunlun mountain river system on the desert groundwater, is meaningful for the local desert hydrogeological study. For these objectives, 105 groundwater samples were investigated to obtain analytical data of groundwater chemistry, and ionic relations methods including ratio graphs and Gibbs plots were applied in the chemical analysis for these data. Chemical analysis shows that desert groundwater is characterized by Cl·SO₄–Na·Mg and Cl⁻·SO₄–Na types with total dissolved solid (TDS) of 2.80–29.77 g/L. Spatial variation patterns of major ions, TDS, and SO₄ ²⁻/Cl⁻ molar ratio reveal clear four hydrochemical zones along the groundwater flow direction on one hand; on the other hand, these variation patterns also indicate that the boundary dividing the influence ranges of the Tarim river and the Kunlun mountain river system is the approximate location of Well 030. Ratio graphs show that the average molar ratios (Na⁺ + K⁺)/Cl⁻ (1.05) and (Ca²⁺ + Mg²⁺)/SO₄ ²⁻ (0.93) are approximately equal to 1, and there is an approximately linear correlation between (Na⁺ + K⁺) and SO₄ ²⁻. These results reveal that the groundwater composition is mainly influenced by dissolution of evaporate (halite, gypsum, and mirabilite). Moreover, ionic relations demonstrate that the dominating hydrochemical processes in the groundwater evolution are evaporation and cations exchange.