Abstract
The project of rural sewerage is spread rapidly and it is contributing largely to the preservation of water quality in agricultural village areas. However, the influence that it exerts on the ecosystem of the river receiving sewage water has not been considered yet. In this paper, we investigated a ‘direct release style’ site where rural sewage was released directly into the river, and we considered the influence of rural sewage effluent on periphyton. The Chl.a that stands for periphyton quantity was high in the remaining area where rural sewage flows in, and a low trend was shown in the downstream area. In the remaining area where rural sewage flows in, species composition of the diatom crowd was changing according to the influence of rural sewage, Saprophilous taxa occupied a great part and, Saproxenous taxa were remarkably few. On the other hand, 19-37% of Saproxenous taxa appeared, although the Eurysaprobic taxa occupied a great part downstream. Diatom Assemblage Index to organic water pollution (DAlpo) that was calculated from diatom was low, and evaluated as polluted in the remaining area, and the downstream area was evaluated as equivalent to the main stream. It was hypothesized that the influence of rural sewage to periphyton is reaching from about 7-10m downstream from the release point.
