Abstract
Abstract In general the research of river ecology focuses mainly on man made construction which can become an obstacle for migratory species or disrupt habitats. However, few studies have discussed the ecological influence of weir or dam operation, like flooding, sediment discharging and construction around the weir. In this study a long term river ecological record of the Ji-Ji Weir in the Chou-Shui River was performed. The methodology include analysis of the richness, diversity and evenness of the fish and crustacean present. Linear regression analysis was also utilized to correlate weir operation with the amount of a particular species. The findings here indicated that areas closest to the weir have experienced a significant decline in the amount of fish and crustacean over the years, whilst sites further away showed an increase following an initial decline during weir construction. In addition, a highly negative correlation between fish number and location relative to the weir strongly suggested a detrimental influence. It was discovered that the Ji-Ji Weir has affected the natural ecology of the Chou-Shui River. The greatest effects were observed at the intercept of the river where flooding and sediment discharge were commonly experienced. Analysis of the operational factors with different fish species suggests that two common species Zacco pachycephalus and Microphysoogobio alticorpus were suitable markers of the fish level index for the Chou-Shui River. We also suggest that Ji-Ji Weir should avoid any intercept of the river when operating, and slow the operating rate of the water gate.