Ion and Sulfate-Isotope Ratios in Arid Soils Subject to Wind Erosion in the Southwestern USA
Our objective was to evaluate the potential for arid-land soil dusts to contribute significantly to the content of SO2-4 and other ions in precipitation. Soil samples collected at 102 locations throughout southwestern USA deserts were extracted with distilled water and analyzed for major ionic constituents and the stable isotope ratios (34S/32S) in soluble sulfate. Most samples were dominated by Ca2+ and HCO-3, and were undersaturated with respect to gypsum. Only a weak correlation was found between Ca2+ and SO2-4 in samples from upland sites. Median δ 34S of soil SO4 was +6.2‰ compared to +3.9‰ reported for precipitation. However, the median ratios for Ca/SO4 (12.00) and Mg/SO4 (1.84) in soil extracts were much larger than the same ratios in precipitation, suggesting that wind erosion of undisturbed desert soils is not a major source of the SO4 in precipitation. Calcite aerosols from desert soils may act to neutralize acid rain in the western USA.
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