抄録
The benthic communities of the River Sasu and the River Se were investigated in July 1975. The prevalent faunae in summer were Ephemeroptera in the River Sasu and Chironomidae in the River Se. In winter, Chironomidae were dominant in the River Sasu and Ephemeroptera in the River Se. At St. 9 and 10 of the River Sasu in winter, the faunae were largely affected by the discharge from a Zinc Mine. In summer, both the numbers of individuals and species were greater than those in winter at these stations. But even in summer at the same stations, few species were recognized compared to the number found at others. At St. 10 and 11 of the River Sasu in summer, the heavy metals content in water increased progressively but faunae were complex too. This may have been caused by successive decrease of the heavy metals in the mud at such stations. The fauna was rich at all stations of the River Se. However, the community structure of the benthos seems to be unstable throughout the year because the dominant species changed between winter and summer at all the stations.
