Investigations of pH, electric conductivity (E.C.) and ionic species of river water were conducted four times per year at 91 sampling sites in 4 basin systems (the Yamatogawa basin system (YaBS), the Yodogawa basin system (YoBS), the Kinokawa basin system (KBS) and the Shinguugawa basin system (SBS) ) within the Nara Prefecture over a period of two years from the fiscal years 2001 to 2002. Consequently, although a large difference was not seen in the four basin systems regarding pH, the order of the concentrations of almost all ionic species, except NO
2-, Br
- and PO
43-and E.C. average concentration was YaBS > YoBS > KBS > SBS. The degree of alkalinity occupied about 50% and ionic components formed 80% or more of all the ionic species by the degree of alkalinity, Ca
2+, Cl
- SO
42-and Na
+, When comparing of pH, E.C., main ionic species concentrations and the average BOD/COD concentrations (mass concentration) in YaBS, which flows in rural city areas, and SBS, which flows in a clean (non-point source pollution area) mountainous district, the rate (YaBS/SSB) of Cl
-, K
+and BOD/COD were 10 or more times greater. As a result of a multivariate analysis (cluster analysis, principal component analysis) with pH, E.C., BOD and COD concentrations, which are pollution index, and ionic species concentrations, the group division could be carried out by cluster analysis in every basin system and these reflected geographic characteristics of each basin system. BOD, COD and ionic species were summarized with the two main ingredients (Z
1, Z
2) from principal component analysis, and the relationship between ionic species, BOD and COD, and the characteristics of investigation points are now understood.
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