水素・酸素および窒素安定同位体組成からみた甲府盆地東部地下水の涵養源と硝酸イオン濃度分布特性

概要

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A stable isotopic technique was used to identify the effects of groundwater recharge on nitrate concentration in the alluvial fans of the eastern Kofu basin. Precipitation, groundwater and river water samples were collected from the Fuefukigawa and Hikawa—Kanegawa alluvial fans. The samples were analyzed for nitrate concentration, water δD and δ18O and nitrate δ15N. A wide range of nitrate concentrations was observed in the groundwater of both alluvial fans. The observed δ15N values suggest that the major sources of nitrate are the fertilizers used in orchards. Similarly, the values of δD and δ18O shows that precipitation and river water are the sources of groundwater recharge for both aquifers. Furthermore, a strong positive correlation was observed between nitrate concentration and δ18O values. Nitrate concentration increases with an increase in δ18O value, where lower δ18O values correspond to river water and higher δ18O values correspond to precipitation. It is suggested that precipitation acts as a carrier and river water acts as a diluent in nitrate loading from terrestrial catchments.
2008-02-10