Responses of attached algal communities to termination of thermal pollution

Post-thermal recovery of attached algae in six artificial streams subjected to three years of thermal pollution was studied for 20 months. Vaucheria, which had been reduced or eliminated by elevated temperatures in some of the streams, returned to pre-thermal abundance within one month. Schizothrix, which had been greatly augmented by heating, decreased to pre-thermal abundance within two months. However, Schizothrix also demonstrated a decreasing tendency to reappear during the late summer at above normal levels, in the stream previously heated the most (12.5 ° C). The epilithic red algae, Rhodochorton and Tuomeya were absent for three years in the stream heated 12.5 ° C above ambient, but returned to pre-thermal levels in three and five months, respectively, when the heating was terminated.