Abstract
Hydrogen isotope, oxygen isotope and water chemistry of surface water were analyzed in the small-forested basin. River water chemistry depended on the runoff of soil water in rainy period, however it did on the runoff of groundwater excluding the rainy period. Ionic concentrations of rainwater were low as compared with those of river water, stream water and groundwater. Streamwater chemistry was almost the same as river water chemistry. Groundwater chemistry, however, was different from river water chemistry due to the weathering and chemical reaction of the sedimentary rocks and soils. It was clarified that stable isotopic ratios of river waters depended on the runoff of groundwater of which isotopic ratios were determined by the height of mountains in the basins, and the differences of the isotopic ratios between rainwater and river water showed whether the surface runoff exists or not.
