Effects of Residual Chlorine on Epilithic Algal Communities in Lotic Systems

Abstract

This study was carried out to clarify the effects of residual chlorine in two rivers on epilithic algal communities. The two rivers of this study are the Onda River and the Itachi River in Yokohama City, receiving the chlorinated sewage effluent. The epilithic algal and water quality were investigated at three sites in both rivers. The number of species of epilithic algal communities was 7 in winter and 5 in summer at the site of high TRC concentration (0.5mg/l) by the sewage effluent, and those was fewer than the number, more than 20, obtained at the site of low TRC concentration (lower than 0.1mg/l). In addition, Chlamydomonas sp. and Monoraphidium fontinale, green algae and tolerant species for chlorine, predominated at the site of high TRC concentration. However, at the site where has the low TRC concentration than 0.1mg/l down from the site of high TRC concentration, diatoms appeared predominantly and the number of species was more than 20 therefore it is confirmed that epilithic algal communities could be recovered.In order to estimate the effects of chlorine on algal growth, artificial clay tiles were placed at each study site. The number of species of epilithic algal communities on artificial clay tiles at the site of high TRC concentration was fewer than 6 species on an average all through the two months investigation period. In addition, by removing artificial clay tiles to the site of high TRC concentration from the site of low TRC concentration, the number of species of algae was decreased, and the structure of communities was replaced the predominant species at the site of high TRC concentration. These results indicated that TRC effects on epilithic algal communities in the river.