Abstract
The study was carried out in order to know the significance of the benthic animals as the indicator of water quality in stream. BOD and the diurnal change of DO were measured in the streams of Toyama prefecture and benthic animals were collected at the same time.
The benthic animals could be divided into two groups, namely group A and B. Group A includes Ephemeroptera, Plecoptera and Trichoptera, and indicates oligosaprobic level. Group B includes Physa fontinalis, Tubificidae, Erpobdella lineata, Asellus hilgendorfii and etc., and indicates α-mesosaprobic level. But in β-mesosaprobic level the species in group. A and B were found together.
The daily minimum DO was shown to be above 70% in summer or above 80% in autumn in the station in which the species of group A were found. And also BOD was above 1.0mg·l-1 in summer or above 1.3mg·l-1 in autumn in the station where those of group B were found.
The relation between BOD and the daily minimum DO was discussed and the diagrams about the ranges of the values of both the daily minimum DO and BOD in each of os, β-ms and α-ms were shown in summer and autumn respectively.
