碳同位素和水化学在示踪贵阳地下水碳的生物地球化学循环及污染中的应用

Chemical and stable carbon isotopic compositions of the ground waters of Guiyang City, China: Implications for biogeochemical cycle of carbon and contamination

地下水污染影响碳的生物地球化学循环,碳的演化也能够反映地下水的污染状况。对贵阳城区地下水的水化学、溶解无机碳含量及其碳同位素进行了分析。研究结果表明,地下水化学以SO4·HCO3-Ca·Mg型和HCO3-Ca·Mg型为主,化学组分分析结果表明,水化学特征主要受岩性控制。地下水中溶解无机碳表现形式主要为HCO-3,丰水期由于稀释作用其含量减少。而丰水期δ13CDIC较枯水期偏负,生物成因无机碳占比重大。结合碳同位素和NO-3等人为活动输入物质的负相关性尝试对城区地下水污染分区,结论为贵阳市区中部、东北部以及西郊农业区地下水受污染较为严重。

Variations in concentration and isotopic composition (δ13CDIC) of dissolved inorganic carbon (DIC) reflect the contamination and biogeochemical cycle of the carbon in ground water. With a main purpose to understand the contamination and biogeochemical cycle of the DIC, a research on the geochemistry of the ground waters of Guiyang City is carried out. The results show that the ground waters are mainly characterized by SO4·HCO3 Ca·Mg and HCO3 Ca·Mg chemical composition. The hydrochemical characteristics of these types of water are mainly controlled by lithology of the aquifers. The average concentrations of Ca2+, Mg2+, <IMG SRC='IMAGE/04150079.JPG' HEIGHT=11 WIDTH=29><IMG SRC='IMAGE/04150080.JPG' HEIGHT=11 WIDTH=22> and in the high flow season are lower than those in the low flow season, which shows a dilution process during the wet season by the mixing of infiltrated meteoric water of low solute content with the aquifer ground water. <IMG SRC='IMAGE/04150081.JPG' HEIGHT=11 WIDTH=29> is the dominant species of the DIC in the ground waters, and has lower concentrations and more negative values of δ13CDIC in high flow season than low flow season. This indicates that more DIC has biogeochemical origin in the high flow season than the low flow season, and that biological activities are the predominant control on shifts of stable carbon isotope values. The δ13CDIC compositions of the ground waters vary in accordance with change in concentration of human activity induced species, this indicates that the anthropogenic input into the ground water systems may have an influence on the aquatic ecosystem of the ground water system. In according with spatial distributions of δ13CDIC and the chemistry of the ground waters, it can be concluded that there is a significant amount of contaminants from human activities put especially into the groundwater in center, northeast and western suburb of Guiyang city.