11:30 AM - 11:45 AM
[HTT18-09] The hydrogen and oxygen isotopic compositions of water in the Chikusa River
In Chikusa River, Chikusa River Conservation Committee has been holding “The simultaneous survey of water temperature all around Chikusa River” in every August since 2002. In this survey, the committee and many local residents measure water temperature at 94 sites, from headwaters to river-mouth and some tributaries. From 2015, Research Institute for Humanity and Nature, Kobe University and University of Hyogo has joined in this survey and started collecting water samples. In the survey of 2018 (held in August 5, 13:00~16:00), we received the water samples from local residents and we filtered them at once, with cellulose acetate filters whose diameters of holds are 0.2 μm. After filtering, we subdivided the samples into some polyethylene bottles and a glass vial and stored them at 20℃ or -30℃. We analyzed stable isotopic compositions of water. Stable isotopic composition of water was lower in the upstream and higher from the middle reaches to the downstream. From the upstream toward the middle reaches, the ratio became lower as the altitude became higher because of the precipitation affected by the altitude effects. On the other hand, the ratio was higher from the middle reaches to the downstream in spite of the altitude. These areas’ river became shallower and wider in the river reforming works, so the effects of sunlight on the river became big and the evaporation from the surface of river became more active.