The Kanto plains is the largest groundwater basin in Japan. Almost all previous studies of groundwater quality had been researched locally, and these studies had been done until 1970′s. There are few studies in isotopic composition of groundwater. In this study, major dissolved ions and stable isotopic ratio of oxygen and hydrogen of groundwater that had been taken from observation wells were determined, in order to clarify the chemical and the isotopic characteristics of groundwater in the major part of the basin.
Groundwater quality showed mainly Ca-HCO3 type, Na-HCO3 type and intermediate type. On the other hand, Na-Cl type and Ca-SO4/ Ca-Cl type were distributed in the specific area and depths. Na-HCO3 type groundwater with relatively high concentrations of dissolved ions is mainly distributed in the central part. Stable isotopic ratios of oxygen and hydrogen decrease toward the inland part, except the central part. On the contrary, isotopic ratio is relatively lower than surrounding part in the depths from shallow to deep in the central part. Three-dimensional distribution of the chemical and isotopic composition suggests that the groundwater area with low isotopic ratio is formed by regional groundwater flow including not only lateral flow but also vertical flow.
Chemical and isotopic characteristics of groundwater that has been obtained by this study contribute to the interpretation of regional groundwater flow system in this basin.
Abukuma Cave located in the southern part of Fukushima Pref. (about 180 km from Tokyo to the north), is a famous huge karst cave. Also, Irimizu Cave is located in the north of the karst area and well known as a cavern. These caves form a large cave system (just like a drainage system in the karst area). There are many karst caves in Japan and they have become tourist spots with various sightseeing plans. However, many unknown things remain from the viewpoint of hydrological sciences. This study tried to make clear the environment and drainage system of the karst cave system.