Estimation on Seasonal Change and Loss by Scouring of Periphyton Biomass in the River.

In Hinuma River, changes of periphyton biomass were observed weekly from September 1987 to March 1990 to evaluate the dynamics of the periphyton biomass in the river. Periphyton were sampled from artificial substrates which were 10cm×10cm unglazed clay tiles. The tiles were submerged in the river more than one month before sampling.At the high periphyton biomass, the ratio of carbon per dry weight of periphyton was low because a significant amount of inorganic particles such as clay and silt was trapped in periphyton. However, the ratio of carbon : nitrogen : phosphorus remained constant regardless of the change of the biomass. From April to October the periphyton biomass was low due to losses by scouring due to frequent storm events. In November and December, the periphyton biomass became greatest because of steady low flow in the river. From January to March, the biomass did not increase significantly due to low temperature even though the rainfall was low.The scouring was found to be a main factor in the dynamics of the periphyton biomass in the river. The amount of the periphyton biomass (as carbon) after scouring was proportional to the exponent of the maximum flow during the storm.