The distribution of the first and the second PC scores for each station and the factor loading of each family of the benthic macroinvertebrate for these PCs in (a) spring, (b) summer, (c) fall, (d) early winter and (e) late winter obtained by PCA are respectively shown in Fig. 3 to summarize which families compose the community structure of benthic macroinvertebrates at each station.The cumulative contribution of PCs 1 and 2 was more than 60% in all seasons. In early winter, the PC score of St. 1 is not shown since it was impossible to take the samples due to the deep snow. The relationship between the location of the score for the stations and the direction of the factor loading describes the details of community structure at each station. Therefore, close positions among the scores show that community structures are similar among the stations. The length of the factor loading for each family shows the intensity for driving the differences of community structure among the stations.