Abstract
To reveal the characteristics of environmental water in Niigata Prefecture in recent years, and to establish a new evaluation method for the behavior of the environmental water, oxygen stable isotopic ratios (i.e., δ18O), concentrations of major ions, pH and EC (electric conductivity) in water samples from several rivers and those from groundwater in Niigata Prefecture were measured. Isotopic measurements were performed with a stable isotope ratio mass spectrometer (Micromass PRISM) . Consequently, the following matters have been found. (1) The δ18O values of river waters in Niigata Prefecture are generally -11 ‰ to 10‰. (2) The δ18O values of groundwater in Niigata Prefecture are generally 1.5‰ higher than that of river waters and the variation is about ± 1 ‰ throughout the year. (3) The δ18O values and the conductivity of groundwater located in the downstream area are higher than those in the upstream throughout the year. (4) The concentrations of major ions of river waters were almost higher in summer and winter than those in spring. (5) The concentrations of major ions in groundwater were higher than those in river water. (6) The concentrations of major ions in river water tend to increase with the downstream from the upstream. (7) The relationship between the conductivity and δ18O values in river water was relatively close (i.e. The correlation coefficient between them is large) in the upstream area (by comparing with that in the downstream) .
