Hydrogeochemical studies on stream water in a forested watershed

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Attempt has been made to describe changing of solute concentration on the rainfall-runnaff processes in a forested watershed. Measurement of water quality, such as pH, electric conductivity, water temperature, concentration of Cl^-, SO_4^<2->, NO_3^-, Na^+, K^+, Ca^<2+>, Mg^<2+>, NH_4^+ and SiO_2, were carried out at two measuring weirs and at 40 groundwater wells, together with the observation of the discharge rate and groundwater level.SiO_2 is dissolved from sail mineral during the process of unsaturated vertical infiltration and temporary saturated lateral infiltration of sail water. The SiO_2 concentration of graundwater settles into one value which is peculiar to each watershed(approximately 18mg/l in the case of Kiryu experimental watershed)at saturated zone. It was estimated that apporoximately from 14 to 16g/m^2 of SiO_2 per year is dissolved at surface sail and its boundary with bed rack and run off to stream in Kiryu experimental watershed. Discussions about variations in concentration of Cl^-, SO_4^<2->, NO_3^- with water cycling in a watershed were also presented.