A study of the relationship between the chemistry of stream water and watershed characteristics was conducted at 20 points in the uppermost basin of the Tama River. The variation in stream SO42- concentrations can be classified into 2 patterns based on geological conditions. In watersheds composed of igneous rocks, SO42- concentration has a correlation with discharge. On the other hand, SO42- concentration has a negative correlation with discharge in sedimentary rock watersheds. In igneous rock watersheds, NO3- and SO42- concentrations have a good correlation with the average slope of the watershed. In contrast, HCO3-, Na+, Mg2+ and Ca2+ concentrations show a negative correlation with the average slope and average altitude of the watershed. The result of the multiple linear regression analysis indicates that the average altitude of the watershed has a greater influence on the HCO3-, Na+, Mg2+ and Ca2+ concentrations than the average slope of the watershed.
Precipitation had been collected by four collectors placed in the northern part of Awaji Island, Japan for two years. The altitudes of the collectors were 440, 240, 35, 5 m above sea level. Hydrogen and oxygen stable isotopic ratios were analyzed for the collected precipitations and spring and well waters in this area. As the results, altitude effects of precipitation were estimated to be -1.1- -1.7‰ δD/100m and -0.25- -0.30‰ δ18O/100m. It was also cleared that the intercepts of the annual-mean-precipitation lines, showing relationships between altitude and δD or δ18O of precipitation, fluctuated in the ranges of 12‰ δD and 1.8‰ δ18O without fluctuation of its slopes. Under such the condition, the conventional method using recharge-water line is not appropriate for the estimation of the mean recharge altitude of spring water.