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