Climatic and geological factors contributing to the natural water chemistry in an arid environment from watersheds in northern Xinjiang, China
A natural water hydrochemical investigation was carried out on three watersheds in northern Xinjiang, China to evaluate the climatic, geological and anthropogenic influence on aqueous major element chemistry in an arid environment. Wide spatial variations are observed in the dissolved solids (TDS) and water chemistry. The hydrochemistry is typically carbonate and alkaline in nature, with Ca2 +, HCO3- and SO42 - dominating the major ion composition. Four major water types, Ca-HCO3, Ca-NDA (non-dominant anion), Ca-SO4 and NDC (non-dominant cation)-NDA or Na-NDA type, are identified in terms of the Piper model. The water chemistry agrees well with the “rock dominance” mechanism, with a TDS value of 80-600 mg/L and a Na+/(Na+ + Ca2 +) ratio of 0.1-0.6. Correlation analysis suggests that most of the ions derive from multiple sources. Stoichiometric analyses indicate that carbonate weathering is the primary source of dissolved ions, followed by silicate weathering and evaporite dissolution. The effects of local pollution have somewhat greater contribution on the oases and central areas of the Zhungarer watershed. Most parts of the rivers show an increasing trend in the dissolved load toward the lower reaches, which is primarily attributed to an evaporation process control along the water course. Variations in water chemistry show clear correlation with the regional lithological distribution, topography and atmospheric precipitation. Using rainwater as a baseline, contributions from atmospheric precipitation and rock weathering to the tributary chemistry are roughly evaluated to be in the range of 2-39% (average 13%) and 59-98% (average 86%), respectively, implying a high effective control of regional geology on stream chemistry compared with that of atmospheric input.