2003 Volume 1 Issue 1 Pages 49-54
Salt water from the sea flows up- and down-ward in tidal rivers due to tides. When mixing in a tidal river is relatively weak, a saltwater wedge is formed in it. The Kita river, the objective field in this study, located in eastern part of Kyushu island in Japan is in this state. When external forces work on an ecosystem, then changes might occur in response to them. The ecosystem in such a river is with more impact, because its aquatic zone in the tidal range is fragile and high in productivity. This study attempts to investigate the behavior of Deiratonotus japonicus, known as a rare species in the world, in association with saltwater wedge movement, to obtain relationships between water quality and hydraulic factors and to study the preferable environmental condition on the habitat of Deiratonotus japonicus. Based on field observations, the habitat of Deiratonotus japonicus has a distribution correlated to salinity and water temperature in the longitudinal direction, and riverbed materials and water surface elevation in the cross-section in the tidal range.
