1961 Volume 74 Issue 875 Pages 228-235
As a first step to study the primary production in the mountain section of the River Arakawa, the standing crop of the sessile algal community was measured by means of the chlorophyll method. From the ecological point of view, the mountain section was divided into two parts; the canyon section and the lower section.
1. The annual mean value of chlorophyll content on the river bed was 25mg./m.2 in the canyon section and 70mg./m.2 in the lower section. These values coincide fairly well with those measured in the ordinary eutrophic lakes in Japan.
2. Throughout the watercourse, definite rhythm was observed in the seasonal changes of chlorophyll content on the river bed. The peaks were found in winter
in the canyon section, while those in lower section were in fall.
3. There is a linear correlation between the chlorophyll content and cell number in the sessile algal community of the mountain river.
4. The main factors determining the standing crop of the sessile algal community in the mountain section of the River Arakawa can be summarized as follows;
(1) unstable aquatic environment of river bed caused by the hydroelectric impoundment, (2) physical action such as scraping and burying referred to the flood of river by heavy rain, and (3) the precipitation of the coarse bed load originated from the construction of the impoundment and of the fine lime stone outflowed from a settling pool of Titibu Mining Industry.