Japan Geoscience Union Meeting 2016

Presentation information

Print

Oral

Symbol A (Atmospheric and Hydrospheric Sciences) » A-HW Hydrology & Water Environment

[A-HW18] Isotope Hydrology 2016

Wed. May 25, 2016 10:45 AM - 12:15 PM 202 (2F)

Convener:*Masaya Yasuhara(Rissho Univ.), Kohei Kazahaya(Geological Survey of Japan, AIST), Kazuyoshi Asai(Geo Science Laboratory), Shinji Ohsawa(Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Futaba Kazama(Social Cystem Engineering, Division of Engineering, Interdiciplinary Graduate School of Medical and Engineering, University of Yamanashi), Masaaki Takahashi(The National Institute of Advanced Industrial Science and Technology), YUICHI SUZUKI(Faculty of Geo-Environmental Sience,Rissho University), Chair:Takashi Nakamura(International Research Center for River Basin Environment, University of YAMANASHI)

10:45 AM - 11:15 AM

[AHW18-06] Investigation of salinization processes in a confined aquifer system; Application of sulfur and chlorine stable isotopes

★Invited papers

*Masaru Yamanaka1 (1.Department of Earth and Environmental Sciences, College of Humanities and Sciences, Nihon University)

Keywords:paleo seawater, diffusion process, confined aquifer

A combination of sulfur and chlorine stable isotopes (d34S and d37Cl) has been used to investigate salinization processes in a confined aquifer system in southwestern Nobi Plain (SWNP), central Japan. Deduced from the SO4/Cl ratios and d34S values, a tongue of brackish confined groundwater (Cl- > 1000 mg/L), which extends from the shoreline of Ise Bay inland, mostly has two salinity sources; One is modern seawater, another is paleo seawater having no SO42- due to sulfate reduction process. The Cl isotopic compositions are negatively correlated with paleo seawater Cl- concentrations, while they are not correlated with either total Cl- concentrations or d34S values. Furthermore, Cl- concentrations from modern seawater are positively correlated with d37Cl values. In addition to these observations, diffusion model calculations suggest that paleo seawater Cl- has diffused in argillaceous freshwater sediments whereas modern seawater Cl- has not been affected by preferential diffusion of Cl isotopes because it has migrated by advection via both an unconfined aquifer and non-pumping wells.