Carbon biogeochemistry of ground water, Guiyang, Southwest China

Variations in the concentrations and isotopic compositions (delta C-13(DIC)) of dissolved inorganic carbon (DIC) reflect contamination and biogeochemical cycling of the carbon in ground water. In order to understand contamination and bioaeochemical cycling of DIC, we carried out research on the geochemistry of ground water of Guiyang, the capital city of Guizhou Province, China. Results show that ground water is mainly characterized by SO4 center dot HCO3-Ca center dot Mg and HCO3-Ca center dot Mg chemical compositions. The hydrochemical characteristics of these types of water are mainly controlled by lithology of the aquafers. HCO3- is the dominant species of DIC in ground water and has lower concentrations and more negative values of delta C-13(DIC) in the high-flow (summer monsoon) season, as compared to the low-flow season. This indicates that DIC is relatively enriched in carbon of biological origin in the high-flow season as compared to the low-flow season and that biological activities are the predominant control on shifts of stable carbon isotope values. The evidence that the delta C-13(DIC) values of ground water decrease with increasing concentrations of anthropogenic species shows that the carbon isotopic composition of DIC can be a useful tracer of contamination, in addition to biogeochernical cycling of inorganic carbon in ground water. Results from this study show that ground water is impacted by significant levels of contamination from human activities, especially in the urban areas, as well as the northeast and west suburbs, in Guiyang city, southwest China.