Chemical and strontium isotope characterization of rainwater in karst virgin forest,Southwest China |
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| Authors: | Guilin Han Yang Tang Qixin Wu Qiu Tan |
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| Affiliation: | 1. Institute for Advanced Study, Shenzhen University, Shenzhen, 518060, China;2. College of Physics and Optoelectronic Engineering, Shenzhen University, Shenzhen 518060, China;3. Key Laboratory of Cenozoic Geology and Environment, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China;4. CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China;5. University of Chinese Academy of Sciences, Beijing 100049, China;6. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan 430074, China;1. State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou 510301, China;2. State Key Laboratory of Environment Geochemistry, Institute of Geochemistry, Chinese Academy of Science, Guiyang 550002, China;3. Chinese Research Academy of Environmental Sciences, Beijing 100012, China |
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| Abstract: | Strontium isotope ratios and concentrations of Ca2+, NH4+, Na+, K+, Mg2+, Cl?, SO42?, NO3? and Al3+, Sr2+ were measured for 52 rainwater samples collected in virgin forest in a rural region between May 2007 and Dec. 2008. The rainwater pH values vary from 4.1 to 7.2 with a volume weight mean (VWM) value of 5.40. 40 of 52 samples have pH value above 5.0, indicating that the regional rainwater was not acidic. Among anions and cations, sulphate concentration (40.4 μeq l?1, VWM) is the highest in the rainwater, followed by ammonium and calcium (30.2 and 20.8 μeq l?1, VWM). Rainwater quality is characterized by low salinity and neutralized pH.The chemical compositions and 87Sr/86Sr ratios of the rainwater samples vary considerably. Using Na+ concentration as an indicator of marine origin, the proportions of sea salt and crustal elements were estimated from elemental ratios. The 87Sr/86Sr ratios were used to characterize different sources base on the data sets of this study and those from literatures. Such sources include weathering of limestone (87Sr/86Sr = 0.7075), remote soil dust (87Sr/86Sr > 0.7135) and anthropogenic source (fertilizers: 87Sr/86Sr = 0.7079). The results of the present study suggest that one likely source for high ammonium and calcium concentration is local soil. Due to a large contribution of these cations to the sulphate neutralization action, the rainwater in this region displays non-acidity, and thus has not significant environmental impact. The wet precipitation in the karst virgin forest in Guizhou province is strongly influenced by natural sources rather than anthropogenic sources. |
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