Application of hydrochemistry and stable isotopes (delta S-34, delta O-18 and delta Cl-37) to trace natural and anthropogenic influences on the quality of groundwater in the piedmont region, Shijiazhuang, China

摘要

Because of their frequent ass(o)ciation with man-made products, increasing SO42- and Cl- concentrations are often important indicators of deterioration of groundwater quality. The integrated use of hydrochemistry and multi-isotopic approaches (delta S-34, delta O-18 and delta Cl-37) was applied in Shijiazhuang area, China, to characterize SO42- and Cl- sources; and to evaluate factors, including natural processes and anthropogenic activities, that affect groundwater quality. In the plain area, the SO42- concentrations of the surface water and shallow groundwater (mean 2.42 mmol/L and 2.06 mmol/L, respectively) were generally higher than those of the deep groundwater (mean 0.69 mmol/L). The natural waters in the mountain area (mean 4.36 mmol/L) had higher SO42- contents than those in the plain area (mean 1.73 mmol/L). The shallow groundwater samples collected in the southern part of the plain area had higher Cl- concentrations than other samples. The SO42- in natural waters showed variable delta S-34 and delta O-18 values, ranging from +8.7% to +21.7% and from +5.9% to 11.4%+, respectively. The delta Cl-37 values fell in a narrow range of -0.22% to +0.64% with a mean value of +0.14%. The hydrochemistry of samples is in part controlled by water-rock interaction processes, but also influenced by anthropogenic activities. The variations of delta S-34 and delta O-18 values indicate gypsum, oxidation of inorganic sulfide minerals, and detergents are the primary sources of sulfate in the samples. Bacterial SO42- reduction is an important reaction affecting the SO42- concentrations in the deep groundwater of the plain area. The plot of delta Cl-37 and 1/Cl- combined with the delta Cl-37 information of potential Cl- sources suggests that the dissolved Cl- in natural waters is mainly sourced from dissolution of Cl-bearing minerals, import of wastewater, and precipitation. Given the above, the elevated concentration of SO42- and Cl- in the groundwater could be mainly attributed to mining activities in the mountain area and input of wastewater from domestic and industrial activities. (C) 2016 Elsevier Ltd. All rights reserved.