Difference of Developmental Patterns of Algal Mats in Slow Sand Filters in Different Water Sources of a Stream Water and a Reservoir Water

Abstract

Seasonal changes of developmental patterns of algal mats of slow sand filters (Someya water works, Ueda city, Wakata water works, Takasaki city and Nabeya-ueno, Nagoya city) were examined. The water sources of Someya water works and Wakata water works were a surface water of a stream and the water source of Nabeya-ueno was a reservoir water. In the cases of slow sand filters which water sources were stream water, an algal mat of filamentous diatom of Melosira grew well due to high nutrient concentration in raw water. It was remarkable in summer when there was high nutrient concentration. However in the case of a slow sand filter which water source was a reservoir water, the developmental rate of algal mat was extremely slow. The dominant species of algal flora on the algal mat on the filter bed were almost same as the flora in the inflow water from the reservoir. Algal mat on the filter bed was just accumulated with phytoplankton which was grown in the reservoir. The low growth rate of algal mat was due to lack of available phosphorus in the inflow water.