Origin and hydrochemical evolution of confined groundwater in Shanghai, China

Confined groundwater is an indispensable resource for the urban security of Shanghai, China, where multi-layer aquifer structures and human activities create a complex environment. An understanding hydrochemical characteristics evolutionary mechanisms necessary its protection effective utilization will be explored in this study. A total 87 samples were collected from five confined aquifers. Hydrochemistry analysis methods such as Durov diagram, Gibbs model Saturation index used to determine origin evolution groundwater. The results show that have two different origins, marine–continental continental, which characteristics. Cl − content 7.5 meq L −1 was demarcation origins. with marine–continental-origin dominated by ancient seawater Na + are derived, whereas Ca 2+ , Mg HCO 3 derived mainly carbonate dissolution. Groundwater continental-origin effects water–rock interaction, major ions silicate weathering In both types groundwater, SO 4 2− insoluble sulfides present low quantities, few high sulfide activities. Cation exchange another controlling factor regarding composition water origins reaction modes follows: reverse cation dominant positive more common continental Over past century, saline has been flowing into funnel region due activities, resulted changes composition. recent influx fresh artificial recharge caused salinization mineral re-dissolution.