Strontium isotope and major ion chemistry of the rainwaters from Guiyang, Guizhou Province, China

Twenty-two rainwater samples from Guiyang city, southwestern China. have been analyzed for their chemical compositions and Sr-87/Sr-86 ratios, with a main purpose to get a better understanding of the general features of rainwater in Guiyang city and their correspondences to human activities. The rainwaters studied are almost acidic (pH=4.53) and show big, changes in major ion composition. Ca2+ and Mg2+ are the principal cations in the rainwaters and their mean values are 56.6 mu mol/L (12.5-163.8 mu mo/L) and 12.8 mu mol/L (4.5-47.3 mu mol/L), respectively. The slim of Ca2+ and Mg2+ accounts for 78%-96% of the total cations in the studied rainwaters. Na+ was the least abundant of the major cations with a mean content of 4 mu mol/L (0.9-7.8 mu mol/L).SO42- is the predominant anion, with a mean content of 94 mu mol/L (33.5-279.4 mu mol/L), coming next is NO3- with a mean content of 48 mu mol/L (2.1-251.8 mu mol/L). SO42- and NO3- together account for 77%-99% of the total anions. Ca2+ and Mg2+ in the rainwater are most likely from dissolution of carbonate minerals in dust or aerosol, unlike K+ that shows more contribution of anthropogenic sources to the rainwater. Na+ does not vary in concentration with Cl-. Significant enrichment of Cl- relative to Na+ as compared with sea water indicates negligible contribution of marine source, which is supported by the evidence that the total rainwater samples show lower Sr-87/Sr-86 ratios (ranging from 0.707934 to 0.709080) than sea water. The rainwater samples are characterized by high contents of No-3(-) SO42-, and Cl- relative to Na+, as compared to the rainwater from other areas in the world, suggesting that the anions (NO3-, SO42-, and Cl-) have mainly of anthropogenic sources. Sr isotope shows potential to trace sources of contaminants when combined with other chemical factors: covariation of Sr-87/Sr-86 ratio with Cl-/Na+ in the rainwater suggest presence of at least two anthropogenic sources for the rainwater samples studied. The coal-combustion industries are probably the major atmospheric contaminant sources in Guiyang city. (c) 2005 Elsevier B.V. All rights reserved.