Abstract
This study was intended to elucidate effects of atmospheric exposure on stream-side for biomass of periphytic algal communities, as estimated with chlorophyll a. Melosira varians-dominated communities, developed on artificial substrates, were investigated in an experimental stream. No distinct difference was found in the maximum reduction rate of the biomass between algal communities exposed to the atmosphere under sunny weather for five hours and those exposed for 24h or 48h. Throughout the seven days after reinundation, the biomass of the communities after atmospheric exposure on stream-side under sunny weather for five hours was maintained at a lower level than before exposure to the atmosphere. In contrast, regarding communities exposed to artificial discharge with no bed-motion, although the biomass decreased after three days, it was greater after seven days than the level before discharge. The effects of controlling the biomass of algal communities were maintained longer after exposure to the atmosphere, as indicated by changes in the ash dry mass that were caused by adherence of the dried periphyton mat on the substrates. That adherence results from exposure to the atmosphere, but the layer gradually peels off in the water current. With exposure of the communities to the atmosphere under cloudy weather for five hours, a slight difference in the biomass was apparent throughout the seven days before and the seven days after exposure. Differences of changes in the biomass of algae in the current in sunny and cloudy conditions indicate that the effects of controlling the biomass differ depending on the weather at the time of atmospheric exposure.
