Abstract
In this study DAIpo (Diatom Assemblage Index to organic water pollution) values of 418 samples were obtained at 183 stations in 52 rivers in the Hokuriku District. The average DAIpo values and the histogram of the distribution of DAIpo values were obtained in several river basins. From there data the state of the organic water pollution of the investigated rivers was examined. In the histograms of the distribution of DAIpo, the modes were of higher grades, suggesting that there are many clean water areas in river basins of that area. Some 25 taxa were chosen as dominant species in the present study. The ecological classification of these taxa according to their tolerance to the degrees of organic water pollution corresponded fairly well with the classification by WATANABE, et al. (1986). A pollution spectrum was made for the above mentioned 25 taxa which showed the change of dominant species according to the degrees of organic water pollution based on DAIpo was made. Its purpose is to determine the suitability of the values of DAIpo as biological informations. As a result, DAIpo values were found to be a proper indicator of water quality in comparatively clean rivers of the Hokuriku District.
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