Controls of Nuisance Filamentous Green Algae in Rivers With Atmospheric Exposure

27 Mar Controls of Nuisance Filamentous Green Algae in Rivers With Atmospheric Exposure

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Abstract

English Abstract

To show effective measures against filamentous green algae that grow in abundance in regulated rivers, in-situ experiments on the effects of atmospheric exposure were carried out using communities of Spirogyra sp. and Cladophora sp. as subjects. In addition, the changes in biomass attributable to atmospheric exposure and discharge were compared. Morphological changes of the chloroplast occurred in most cells of Spirogyra sp. and Cladophora sp. with atmospheric exposure. The biomass of Spirogyra sp. communities decreased by about 90—98% in cases of one-day atmospheric exposure, three-day exposure, and discharge after three-day exposure. The latter case exhibited the greatest biomass decrease. It was the only case in which the ash free dry mass decreased. The biomass of Cladophora sp. communities decreased by 84% in both cases of discharge after one-day atmospheric exposure and three-day atmospheric exposure. In those cases, the ash free dry mass also decreased markedly after atmospheric exposure. Although the relative abundance of filaments of Cladophora sp. accounted for about 80% of the communities before atmospheric exposure, the relative abundance of other algae increased more than 75% after atmospheric exposure. Both filamentous green-algal communities were abundant after discharge, however they were decreased markedly by atmospheric exposure, suggesting that atmospheric exposure is an effective method for control of filamentous green algae in regulated rivers.