溶存成分組成から見た山地の水循環における水質変化:─新潟・山形県境金丸地域の例─

概要

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In order to clarify the change in the geochemical characteristics of water during hydrological cycle in mountainous and forested region, we studied chemical compositions of precipitation, streamwater, spring water and groundwater in the Kanamaru area, northeastern Japan, since 2002 to 2005. The groundwater was taken from 50 meters deep nine wells in a foot part of mountainous region where the Cretaceous granites and overlying Miocene sedimentary rocks are distributed. Each well was drilled through both the sedimentary rocks and granitic basement. The precipitation, streamwater and spring water were collected from the area surrounding the wells. The precipitation, streamwater and spring water show seasonal change in electric conductivity (EC) and concentrations of Cl－ and Na+; they are higher in the winter season and lower in the summer and snow-melt seasons. The geochemistry of groundwater is characterized by increase of pH, EC and concentrations of Ca2+ and HCO3 － and decrease of dissolved oxygen and Eh with increasing depth.