An ecological assessment of a dammed pool formed by a slit check dam

摘要

This study surveyed physical, chemical, and biological parameters in a dammed pool in comparison to those of the adjacent main stream. Because the dammed pool in this study was a unique zone formed by a slit check dam, the properties of the pool and the main stream could be considered representative of the conditions with and without a slit check dam, respectively. Data were collected in the dammed pool and in the reach of the main stream above the slit check dam in the Wasada Stream, Miyagi Prefecture, Japan. The dammed pool exhibited a lower velocity and finer substrate than those of the main stream. In addition, the water temperature in the dammed pool was slightly higher than in the main stream. Dissolved Oxygen and Chemical Oxygen Demand in the pool were lower than the allowable standards for water pollution. The pool exhibited worse biological indices of water quality than the main stream. Out of a total of 18 taxa found in the stream, only 5 taxa were found in the dammed pool. Most individuals in the dammed pool belonged to the genus Chironomus, which tends to colonize heavily polluted sites. According to these various indicators, the water quality of the dammed pool was lower than that of the main stream. The longest durations of the presence of the dammed pool mainly occurred during snowmelt and during the rainy season. The average duration of the presence of the dammed pool was calculated as 14 days. The dammed pool exhibited a short-duration cycle of formation and extinction according to seasonal variations in water discharge. This cycle reduces the negative effects of the pool on water quality. Therefore, the dammed pool has a minimal negative effect on restoration of the entire reach of the Wasada Stream.