| Yangzhou-Taizhou-Jingjiang area, located in the northern part of the Yangtze River Delta, includes the southern part of Yangzhou and Taizhou region and Rugao region, with abundant pore water in the Quaternary deposits. Since the previous studies on the conditions of recharge, runoff and discharge and the origin of groundwater were insufficient, it is difficult to rationally exploit and effectively manage groundwater resource, and has resulted in long-term over-exploitation of groundwater and continuous drop of water table, which would easily cause leakage recharge and contamination from shallow groundwater to deep groundwater system. Meanwhile, as the top section of the Yangtze River Delta, Yangzhou-Taizhou-Jingjiang area belongs to the recharge area and the initial runoff area of groundwater system. Therefore, contamination of groundwater will inevitably threaten groundwater quality of the entire Yangtze River Delta. According to the isotopic and hydrochemical components in groundwater with rich information on water cycle, it had been analyzed comprehensively with methods of isotope hydrology and hydrogeochemistry in this paper.Through analyzing the characteristics of D, 18O, T and hydrochemical components, the results indicate that in Yangzhou-Taizhou-Jingjiang area phreatic water receives recharge both from local precipitation and Yangtze River water, and has close hydraulic connection with surface water; confined water is mainly recharged from ancient water, and has poor hydraulic connection with phreatic water and Yangtze River water. The average values of D and 18O in phreatic water (-45.5‰,-7.43‰) are similar with that of precipitation (-44.83‰,-7.36‰), and has good correlation with that of Yangtze River water (R2=0.93). In the section along the Yangtze River, phreatic water has been laterally recharged and diluted, and the contour line of Cl-concentration (60mg/L) is almost parallel to the coastline of the Yangtze River. The hydrochemical types of surface water and phreatic water is similar, mainly HCO3-Ca water, with significant resonance in concentrations between them. The isotopic and hydrochemical characteristics of confined water are different with phreatic water, and the hydrochemical types gradually change from HCO3-Ca water in the 1st confined aquifer to HCO3-Ca·Na water in the 2nd confined aquifer and to HCO3-Na water in the 3rd confined aquifer.According to the study of sulfur isotope and hydrochemistry, it shows that Surface water and phreatic water are subjected to a certain degree of contamination, withδ34S values about 10‰, and confined water is basically not contaminated, withδ34S values closely related to the hydrogeological conditions in different sections of the studied area. In shallow confined water along the Yangtze River and at the top of the study area, sulfates with negativeδ34S values originate from oxidation of sulfides, which is related to the sand-dominated lithologic character, good runoff condition, poor sealing property and aerobic environment. In deep confined water of the central section, sulfates withδ34S values more than 20‰are related to the clay-dominated lithologic character, poor runoff condition, good sealing property and anaerobic environment. And due to reduction of sulfates, someδ34S values is up to 70‰. The positive correlation between sulfate concentrations andδ34S values proves that sulfates in the central section recharge from runoff and detained marine sulfate.By means of calculating 14C age of groundwater and hydrochemical profile analysis, it illustrates that the overall flow direction of the confined water is from west to east with hydrodynamic situation gradually slowing, contents of soluble components, such as Na+ and Cl-, increasing, contents of insoluble components, such as Ca2+, Mg2+ and HCO3-, decreasing, and groundwater age increasing. Ion exchange occurred significantly in the process of groundwater runoff. Along the Yangtze River and at the top of the study area, age of the 1st and 2nd confined water was less than 5000 years, and gradually increased to 20,000 years of the 3rd confined water in the eastern part of the study area.
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