Inorganic ions besides nitrogen and phosphorus have influence on the eutrophication of lake. The secular increase of inorganic ion loadings from a river basin by the accumulated influence of the massive fertilizer injection in agricultural land and air pollution including acid rain are forecasted. The specific loadings of inorganic ions for ten river basins were estimated on the basis of weekly observation data for one year. From the correlation analysis between specific loadings of inorganic

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... ns and area ratios of land-use types in river basins, most of inorganic ions showed high correlation coefficients for urban and agricultural areas. But nitrate ion only become a high correlation coefficient for farmland area. In the correlation analysis among inorganic ions, those except nitrate ion have high correlation coefficients with one another. The seasonal changes in concentrations and loadings of inorganic ions were chiefly ruled by discharge and slightly by water temperature. In the period of storm runoff the concentrations of most inorganic ions did not steeply decrease and those loadings increased fairly. Particularly, the increase of potassium concentration among the cation group at the biggest peak of discharge during a storm runoff was recognized as well as nitrate and sulfate ions among the anion group.