2020 Volume 76 Issue 1 Pages 1-9
The objective of this study was to clarify characteristics of runoff and stream water chemistry in forest and grassland watersheds in the headstreams of the Okuragawa River, Sado Island, Niigata Prefecture, Japan. The factors controlling the difference in characteristics of runoff and stream water chemistry between two watersheds were also discussed. Continuous monitoring of precipitation and discharge, periodic stream water sampling, and the water quality analyses of major ions and stable isotope (oxygen and hydrogen) composition were carried out in both watersheds. In the forest watershed, the response to precipitation was slower, the peak discharge was clearly lower, and the decrease in discharge after rainfall was more gradual than those in the grassland watershed. For the relationships between the discharge and the stream water chemistry, concentration of Ca2+, Mg2+, Na+, and HCO3- and Electric Conductivity (EC) decreased with increasing discharge in both watersheds. The degree of decrease in stream water chemistry of the forest watershed was markedly smaller than that of the grassland watershed. The result was consistent with the difference in runoff characteristics between both watersheds and also suggested that dilution effect on the stream water chemistry during rainfall was not significant in the forest watershed compared to the grassland watershed.
PROCEEDINGS OF HYDRAULIC ENGINEERING
