1. Origin and geochemical evolution of porewater in clay aquitards in North Jiangsu coastal plain, China Qin Ge 1, Xing Liang 2, Jing Li 1, Bin Ma 1 1 School of Environmental Studies, China University of Geosciences, Wuhan 430074, Hubei, China Email: geqin90827@126.com 2 Hubei Province Key Laboratory of Wetland Evolution and ecology restoration, School of Environment Studies, China University of Geosciences, Wuhan, 430074 1 Introduction Directions of syntheses Hendry et al (2000) showed that the transport of dissolved salts and their isotopes of pore waters attributed to diffusive mixing and the geochemical reactions could be neglected Timms and Hendry(2007) indicated cation exchange also occurred in the pore water over the long pore waters residence times in the clay aquitards Jing Li et al. (2012) pointed that the chemical composition of pore waters would be influenced by reduction of sulfates and cation exchange In this study, several major chemical ions analysis and stable isotopes are obtained form the pore waters in aquitards under the influence of groundwater exploitation, surrounded by quaternary marine deposits and closed to the South Yellow Sea, are applied to better assess the origins and geochemical evolutionary processes of pore water. (1) analyze the distribution and characterization of hydro-chemistry and isotopic signature of pore water (2) ascertain the major genesis of porewater in relation to salinity sources, mixing behavior between seawater and freshwater (3) attempt to determine the geochemical evolutionary processes by taking advantage of the geochemical indicators. 2 Objectives 4 Results 5.1 Origin of pore water 3 Pore water extraction methods 5 Discussion (1) Han D, Kohfahl C, Song X, et al. Geochemical and isotopic evidence for palaeo-seawater intrusion into the south coast aquifer of Laizhou Bay, China[J]. Applied Geochemistry, 2011, 26(5): 863-883. (2) Hendry M J, Wassenaar L I. Controls on the distribution of major ions in pore waters of a thick surficial aquitard[J]. Water Resources Research, 2000, 36(2): 503-513. 7 References 6 Conclusions Porewater mostly originate from meteoric precipitation. Diluted paleo-seawater and later seawater intrusion are the major formation mechanism of salinity in saline porewater., while the salinity of brackish porewater was mostly deriving from evaporation and halite dissolution. The highest seawater mixing proportion reached 81.6% and cation exchange exists in all simulations of saline porewater. The evaporation process of brackish porewater that increased the concentration of salts and promoted the solid phase of CaSO 4 and CaCO 3 dissolving B 5.2 Geochemical envolution of porewater A. The evolutionary mechanism of saline porewater as a result of halite precipitation and seawater mixing B. Cation exchange process analysis C. Other evolution regimes of porewater, e.g. water rock interaction C 1.Top seal and piston 2.Steel tube 3.Filter mesh and membrane 4.Bottom seal 5.drainage hole Salinity, solutes, stable isotopes ( 18 O, D ) 1. Saline porewater were probably derived from evaporated seawater or later seawater intrusion and subsequently diluted by freshwater 2. fresh porewater samples preserve the signatures of paleo- precipitation; the salinity of brackish porewater was mostly deriving from evaporation and halite dissolution. C A