JpGU-AGU Joint Meeting 2020

Presentation information

[J] Poster

A (Atmospheric and Hydrospheric Sciences ) » A-HW Hydrology & Water Environment

[A-HW34] Isotope Hydrology 2020

convener:Masaya Yasuhara(Rissho Univ.), Kohei Kazahaya(Geological Survey of Japan, AIST), Shinji Ohsawa(Institute for Geothermal Sciences, Graduate School of Science, Kyoto University), Kazuyoshi Asai(Geo Science Laboratory)

[AHW34-P02] The influence of geology on river water quality and chemical loads in Oshika Village, Nagano, Japan

Miyuki Mori1, *Masaya Yasuhara1, Seongwon Lee1, Yuri Hirano1, Fumitake Kusuhara2, Noritoshi Morikawa3, Kohei Kazahaya3 (1.Rissho Univ., 2.Central Research Institute of Electric Power Industry, 3.Geological Survey of Japan, AIST)

Keywords:geology, river water quality and load, heavy metal, ultramafic rock, crystalline schist, granite

Ohshika Village, Nagano Prefecture, central Japan is characterized by various types of rocks with different chemical composition, different grade of metamorphism, ages and origins. It is expected that these rocks and geological conditions may control water quality and chemical loads of the rivers across the village. The purpose of this study is to clarify the relationship between the river water quality/loads and geology through analyses for major ions and heavy metals.
From the trilinear diagram, water quality in the study area proved to be characterized by the Cl-, Ca2+ and Mg2+ concentration. A large amount of Cl- is loaded from the pelitic schist and green schist, while Mg2+ from the serpentinite. Also, a large amount of SiO2 is loaded from the diorite, gneiss, sandstone and mudstone, and Ni is loaded when the river flows down the area composed of the serpentinite, pelitic schist, sandstone and mudstone. Little loading of SiO2 was found from the serpentinite. The higher the areal proportion of the serpentinite in the drainage basin, the higher the Mg2+ concentration and the lower the Ca2+ and SiO2 concentration of the river water.