Evaluation of River Water Quality with Multivariate Analysis in Clear Stream Watersheds in Agricultural Area

We analysed the river water quality of Rekifune River and Satsunai River watersheds, which are evaluated as a clear stream in Tokachi region, Japan with the principal component analysis (PCA) and the cluster analysis to interpret complex water quality data and to evaluate factors affecting river water quality on the basis of a 2008 investigation. The mean pH was neutral and stable, also the mean BOD, SS and EC were relatively low. However, T-N concentrations tended to be high in Satsunai River watershed. The PCA and cluster analysis integrated the trend of water quality to two main components and classified the sampling points into three clusters. From the results, the river water quality of Satsunai River watershed was deteriorated by agricultural impacts, whereas the river water quality was preserved in Rekifune River watershed. Furthermore, three sampling points affected by the point source were classified in both river watersheds. It is necessary to develop a framework of agricultural impacts on Satsunai River watershed to improve the river water quality. An equally important priority is to control the loads from agriculture in some parts of Rekifune River watershed to maintain good water quality.