Nitrification Activities of Streambed Biofilms and Sediments at Rapids and a Pool

Abstract

Several surveys were conducted to investigate nitrification activity and pyramid of biomass in periphyton biofilms at rapids and a pool in a local river. The nitrification activity was higher at the pool than the rapids on the basis of the river bed area. However, the relationship was reverse on the basis of volatile solid mass. The potential rate of nitrification was around 40mg/m2 per day, which corresponded to a few percents of the amount of nitrogen in the periphyton biofilms at the rapids. The mass of feeding benthos ranged from 5 to 10 % of standing periphyton biomass on river bed stones from autumn to winter. The percentage is in good agreement with the value of 1/10 which is known as a ratio of the phytophagous animals to the primary producers in the pyramid of biomass. Particulate nutrients were settled more densely at the upper part of river bed than deeper part. A phenomenon of trapping particulate nutrients was observed in the transient region of river beds from pool to rapid due to infiltration flow.