Characteristics of Ion Components of Clearwater Stream Watershed in an Agricultural Area with Multivariate Analysis

Abstract

Restoring the clear-stream environment that once existed in agricultural areas is one of the major challenges for the development of sustainable agriculture. Therefore, we analyzed the ionic components of the Rekifune and Satsunai River basins, which are regarded as clear-water basins in the Tokachi region of Hokkaido, using principal component analysis and cluster analysis based on surveys conducted in June and September 2014. The results showed that most of the sampling points in the Rekifune and Satsunai drainages were comparable to the average values of water quality assessed as clear-streams in Japan. However, in the tributaries of the Rekifune River, since Cl^- and Na⁺ increased characteristically, the water quality was degraded by anthropogenic pollution sources such as domestic wastewater. In the Satsunai River, the water quality of the downstream tributaries was degraded due to agriculture. In addition, in one of the tributaries, deterioration of water quality was observed only in September, and the water quality of the main river immediately after the inflow of this tributary was also affected. These results indicate that the water quality in the two basins in the predominantly agricultural area is generally good. Still, it is necessary to identify the source of pollution in some areas and take countermeasures.