[A-HW17] 水循環・水環境

[AHW17-03] 同位体組成と化学成分からみる「とやまの名水」の特徴と起源の検討

*片境 紗希¹、張 勁²、上田 晃² (1.富山大学大学院理工学教育部、2.富山大学大学院理工学研究部)

キーワード：地下水

Total eight spots of spring water from Toyama Prefecture were selected as ‘The 100 Exquisite and Well-Conserved Waters (EW water)’ by Ministry of the Environment in Japan. However, with enhancement of groundwater usage in recent years, water quality and flux diminished gradually. To understand the origins and water qualities of these spring water, we measured hydrogen and oxygen stable isotopes, together with chemical composition of spring water, groundwater, rivers, and rainfall in Toyama Prefecture. All EW water in the Toyama Prefecture lied in the middle of meteoric water line with d-value (δD-δ¹⁸O) of 30 in winter and 10 in summer. This suggests that EW water was well-mixed and balanced by precipitation in all seasons. Muratsubaki located in the edge of Kurobe alluvial fan, has very similar mineral composition with nearby confined groundwater, suggests having the same catchment origin with Kurobe River. Using δ¹⁸O and water property data, this spring water is known that originated from high mountain area with 1658m elevation and well forested. Furthermore, downstream show higher SiO₂ and lower Na/Ca ratio relative to upstream, well agreed with longer residence time in the downstream (0-5 yrs) comparable with previous study. In contrast, no significant difference of SiO₂ and Na/Ca versus δ¹⁸O between groundwater and river in the Sho River fan, implying short transit time from river to groundwater. This study highlights the importance to examine groundwater source to sustain high quality EW water, e.g. paying attention to water preservation in the forest area.