CHARACTERISTICS OF RIVER WATER QUALITY IN TWO ADJACENT WATERSHEDS WITH DIFFERENT LAND USE

Abstract

This paper evaluated the effects of land use on river water quality in the Kishi and Zakuro Rivers. Both basins are mainly covered by forest and orchards, and especially about 30% of the Zakuro River watershed is orchard. In the field observation, the concentrations of NO₃^- and Mg²⁺ in the Zakuro River were observed to be higher than those in the Kishi River from autumn to spring. However, there were no differences in the concentrations of the other ions and COD between both rivers. In order to examine these results, especially the effects on the concentrations of NO₃^- and COD, nitrogen and COD loadings were calculated using pollutant load factors. The calculation result of nitrogen loading implied that the discharge of nitrogen from the orchards played the most important role in the change in the NO₃^- concentration of the Zakuro River. In the meantime, there were no differences in COD loadings between both basins and therefore the COD concentrations would be approximately equal.