Stable Isotope Ratios of Groundwater in Gogo Island, Ehime Prefecture

概要

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Various water qualities, especially stable isotope ratios, of groundwater in shallow wells were measured, together with groundwater levels, in Gogo Island, Ehime Prefecture. In a coastal region of the Yura district, chloride ion concentration far greater than 200mg·1-1 (the standard value of city water) was always found and the δD versus δ18O diagram suggests that the groundwater in this region is a mixture of seawater and upstream groundwater. Non-dimensional values of δD, δ18O and Cl- of groundwater near the bottom of a well in a coastal region of the Yura district indicate almost the same value, and it was estimated that groundwater contained approximately 20% seawater. The vertical distribution of non-dimensional Cl- is different from those of δD or δ18O. The former indicates higher concentration in the upper part of the well. The higher concentration may be caused by the Cl source except seawater, e. g. fertilizer.
Japanese Association of Groundwater Hydrologyの論文