Succession of Epilithic Algae and Water Quality Environment in Urban Small Streams

The survey was conducted to clarify the succession of the epilithic algal communities in two small streams (the River Tsunaki and the River Zaru) during Apr.1997-Apr.1998. The riverhead of two streams is almost same. The River Tsunaki is a branch of the River Hirose, a symbolic river in Sendai City, receiving the ozonated sewage effluent. While the River Zaru is a branch of the River Natori, receiving the effluents from housing developments.The epilithic algae and water quality were investigated at eight sites (three in the R. Tsunaki and five in the R. Zaru) every month. The average of water temperatures were 11-18°C, velocities were 0.25-1.12m/s. The average concentrations of BOD were 0.7-1.2 (the River Tsunaki), 0.6-2.2 mg/l (the River Zaru) . The many nutrient concentrations were constantly high at the downstream site in the R. Tsunaki by the sewage effluent.The average amounts of chl.α were 76-470 mg/m2. The amounts of chl. α were tended to increase during winter. Among the algal species identified (77 species in the River Tsunaki) and (80 species in the River Zaru) Homoeothrix janthina, Stigeoclonium lubricum, Rhoicosphenia abbreviata, Nitzschia inconspicua and Cymbella minuta to dominated. At the site of rapid velocity the filamentous algae dominated, and at the sites of upper 0.5 m/s velocity the relative abundance of filamentous algae and the velocity related in high ratio (r=0.70) . And it was found that the epilithic algal communities in each river divided four groups during a year by cluster analysis bases on C∏ similarity and the sewage effluent effected the epilithic algal communities.The present results showed the efficiency of algal community for monitaring river environments.