干旱区生态环境知识资源中心

The major ions and Sr concentrations and the Sr isotopic compositions of rainwater from four weather stations in the Ordos desert, Northwest China, were measured in this study. In the studied rainwater, Ca2+ was the most abundant cation with a volume-weighted mean (VWM) value of 387 mu mol/L, and SO42- was the dominant anion, with a VWM value of 229 lmol/L. The Sr concentrations varied from 0.1 to 72 mu mol/L, and the strontium isotopic ratios (Sr-87/Sr-86) range from 0.7098 to 0.7110, with an average of 0.7106, which are higher than that of seawater. The Sr-87/Sr-86 ratios showed the potential to trace sources of rainwater solutes when combined with other chemical composition data. The covariation between Mg/Ca vs. Ca/Na and Sr isotopic ratios vs. Ca/Sr in the rainwater suggested the mixture of at least three sources: soil dust derived from the local area and/or desert and loess areas in northwest China (Sr-87/Sr-86 values of 0.7114), seawater (Sr-87/Sr-86 value of 0.70917), and anthropogenic inputs (Sr-87/Sr-86 value of 0.7110 and high Ca/Sr, due to coal combustion or automobile exhausts). The human activity inputs are likely the major sources of atmospheric contaminants in the Ordos rainwater. From back-trajectory analysis, principal component analysis and a comparison between the major ion compositions of other selected sites in China, we conclude that the Ordos rainwater ion composition is more significantly influenced by desert and soil dust and anthropogenic sources (primarily industrial and traffic emissions from the surrounding cities) than by marine sources.