SEASONAL INFLUENCE OF WATER DISCHARGE FROM DAM ON STREAM BENTHIC ANIMAL COMMUNITY

Abstract

To understand the seasonal influence of water discharge from a dam on stream benthic animals, biological and environmental surveys were conducted monthly from May 2000 to April 2001 at sites above and below the Okura dam. At the lower site, total population density increased, and Shannon-Wiener diversity index decreased during the month of September and November. This was a consequence of seasonal outbreak of Hydropsyche orientalis, which mainly feeds on Fine Particulate Organic Mater, and FPOM was highly supplied to the tail water in the said period. The Sorenson's similarity index across the dam showed seasonal prevalence in which the level increased from July to September, decreased during November and December, and recovered from January to March.