Dominant Growth of Filamentous Diatom Melosira under Natural Environment in Comparison with a Slow Sand Filter.

Abstract

Natural field survey was done to clarify the characteristic environment for a filamentous diatom Melosira to dominate in a slow sand filter. Four natural fields where Melosira was dominated in early spring were observed periodically. There were the basin of Shiraito waterfall at the foot of Mt. Asama, a natural pond of Sato Ike at the foot of Mt. Asama, pools in a dry river bed of River Chikuma where is a lower reach of sewerage plant and a hydroelectric power plant, a small downstream of Karasawa fall, and Soehi stream of a mountain small stream with slow water current as a contrast place where was not observed Melosira. The places where Melosira was observed at always in a year were a basin of Shiraito fall and pools in a dry river bed of River Chikuma. The basin was periodically cleaned to keep a clean basin. The pools were flushed out after the heavy rain and irregularly water discharge from the power plant. Both place are similar to a slow sand filter basin where the surface mud is scraped periodically. Small stream of Karasawa fall was hidden in the grass in summer. There was sometimes a evening shower in the mountain area and there was a sudden high water after a shower. In the pond Sato Ike, filamentous diatom was observed during the low water temperature period from fall tospring. However a filamentous green alga was dominated in summer. Filamentous diatom was apioneer plant in a stable environment with a slow water current and it was replaced tofilamentous green algae in warm period. The cause of this succession was discussed with the grazing activity of aquatic insect larvae.

Abstract

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