Characteristics of dissolved matters in stream water and separation of runoff components of storm events

Abstract

The changes of concentrations of dissolved matters in stream discharges were investigated before and after four storm events. Moreover, the relationships between the groundwater pathways and changes of stream qualities were discussed by the separation of the runoff components using alkalinity (to values as small as pH 4.8). The study was conducted on two adjacent catchment basins (a young stand, 1.3 ha, and an established stand, 1.8 ha) located in the University Forest of Tokyo University of Agriculture and Technology in Gunma Prefecture. K⁺, Ca²⁺, Mg²⁺, NO₃^--N, and SO₄^2--S concentrations and electric conductivities increased with increases in stream discharges and decreased with decreases in discharges for events with more than 100mm of total rainfalls. The opposite tendencies were shown by Na⁺, Cl^-, HCO₃^-, SiO₂, and pH, but these tendencies did not appear clearly with events of about 40mm of total rainfalls. The positive correlation coefficient of the variations of two factors recognized relationships between NO₃^--N, Ca²⁺, and Mg²⁺ concentrations, and electric conductivities. The rates of base flows to the totals of peaks stream discharges were 29% in the young stand and 53% in the established stand for a event with 189mm of total rainfall. These rates were 90% in both catchment basins for a event with 45mm of total rainfall.