贵阳市区地表/地下水化学与锶同位素研究

CHARACTERIZATION OF WATER-ROCK INTERACTION AND POLLUTION OF KARSTIC HYDROLOGICAL SYSTEM: A STUDY ON WATER CHEMISTRY AND Sr ISOTOPE OF SURFACE/GROUND WATER OF THE GUIYANG AREA

贵阳市及邻近地区地表和地下水的化学与Sr同位素组成变化反映了典型喀斯特地区地表/地下水文系统的水-岩反应和城市污染特征:水体中的化学溶解物质主要来源于碳酸盐岩(石灰岩和白云岩)的风化作用和膏岩层的溶解,其次为人为污染物的输入;污染物以K+,Na+,Cl-,SO2-4,NO-3为主,枯水期因大气降水补给小而受人为活动影响较大;丰水期和枯水期地表/地下水的化学组成变化说明地表/地下水交换活跃,地下水环境容易受到人为活动影响。

The chemistry and Sr isotopic composition of surface/ground waters of the Guiyang city and its adjacent areas represent a typical hydrogeochemical signature of a typical karstic hydrological system. Dissolved load of surface and ground waters are mainly dominated by Ca^2＋, Mg^2＋, SO4^2- and HCO3^-, which are derived mainly from chemical weathering of carbonate rocks （limestone and dolomite） and dissolution of sulfate evaporates. Contribution of silicate weathering to the water system is very small. The variations of major cation compositions, such as Mg^2＋/ Ca^2＋ and Sr^2＋/Ca^2＋ ratios, are controlled by both weathering sources and water-rock interaction. The Sr isotope compositions of the sewage samples show no significant differences with those of the surface and ground waters, and hence can not be used to trace the contaminant cycling. However, Sr isotope, when combined with chemical composition, can be a powerful tool to trace the source of contaminants. Anthropogenic inputs to the ground water system are mainly K^＋, Na^＋, Cl^-, SO4^2- and NO3^-, among which the Na^＋ , Cl^-, SO4^2- and NO3^- components can be used as the indicators of the ground water pollution. These contaminants are of higher concentrations in winter-season water, as a result of a smaller volume of water and hence smaller buffering capacity the water system. The ground waters have more NO3^- than the surface water, indicating that the NO3^- can be accumulated or present for a long time in the ground water system. The ground waters show co-variations in chemical composition with the surface water, and show significant differences in chemical composition in winter- and summer-season. In addition, the chemical compositions of the studied waters show a mixing of surface and ground waters. The obtained geochemical evidence demonstrates that the surface and ground water in the karstic hydrological system exchanges quickly and hence is an easily subject to impact of human activities.