興居島における地下水の安定同位体比

抄録

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.