紀の川の水質特性と土地利用の関係

抄録

Soluble substances of the Kinokawa-river increased down the stream. Excluding weathering of limestone, soluble substances in the upper stream of the catchment covered with forest were very low and main components were HCO^-₃, SO^2-₄, Na⁺, and Ca²⁺. Soluble substances in the upper stream of the forest catchment with limestone were high and the main components were Ca²⁺ and HCO^-₃ Ca²⁺ and HCO^-₃ concentrations increased from the upper stream to the middle stream with forest, but Na⁺, Cl^- and SO^2-₄ concentrations remained unchanged because of weathering of limestone and feldspar. In the lower stream of the catchment with farm land and housing site, the concentrations of Na⁺, Cl^-, NO^-₃ and SO^2-₄ were very high. It was concluded from the relation between land uses and water qualities that Na⁺ and SO^2-₄ origin were farmland, and Cl^- origin was sewage respectively, and NO^-₃ was derived from both origins. Isotopic study of oxygen and hydrogen indicated that the river water originated from precipitation and isotopic ratios depended on mainly precipitation altitude.