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Effects of a Rivermouth Barrage on Planktonic Algal Development in the Lower Nagara River, Central Japan.

1998; Volume: 59; Issue: 3 Linguagem: Inglês

10.3739/rikusui.59.251

1882-4897

Tetuo MURAKAMI, Nobuo Kuroda, T Tanaka,

Freshwater macroinvertebrate diversity and ecology

The biomass and flora of planktonic communities before and after construction of a river mouth barrage in the lower Nagara River, (Central Japan) are described in relation to long-term trends in some environmental factors. Despite a lack of environmental trends which might accelerate algal production (except for the prolonged retention time of river water), the algal occurrence modes, such as maximal biomass or occurrence period, changed remarkably after construction. Cyclotella atomus and C. meneghiniana (diatom) remained dominant in summer as they were pre-construction. Longitudinal increases or decreases in algal biomass along the stream resulting from a balance between production and sedimentation, which were dependent on the discharge, were recorded. Additionally, grazing by rotifers seemed to be widespread in midsummer. The lower Nagara is regarded as a river-lake hybrid based on its role as a primary producer of algal biomass and its manner of controlling it. However, unlike a lake, it varies in its extent both spatially and temporally.