On the other hand, the first quadrant has the factor loadings for many kinds of family and the score for St. 7 was distributed into this quadrant. Hence, these results indicate that community of benthic macroinvertebrates is recovered at St. 7 in the lowest reaches of the River Akagawa. Moreover, Chironomidae and Hydropsychidae are considered as
important indicators for the recovery of benthic macroinvertebrate abundance in the River Akagawa because these families are predominant in St. 7 and their factor loadings are distributed into the first quadrant in all seasons. Additionally, since St. 5 was distributed into the second and third quadrants, and St. 6 was distributed into only the third quadrant, it would appear that the second quadrant describes a stage of transition from the third quadrant that has a simple community structure consisting of acid tolerant macroinvertebrate to the first quadrant including St. 7.