Abstract
Lake Jusan is a brackish lake located in the down reaches of Iwaki River system and is one of the most famous places for Corbicula japonica in Japan. The aquatic environment in the lake and the river has long been changing under numerous natural and anthropogenic factors. The former includes changes in meteorological and hydrological systems, while the latter is composed of river improvement works, reclamation for farmland, etc. In this study, we first focused on topographical changes in Lake Jusan caused by the reclamation project completed in 1969 and by sedimentation. The influence on salinity fluctuation in the lake was investigated using computational hydraulic simulation and was found rather small. We then assessed influence of hydrological changes. In 1950s before large dams were constructed in the basin, drought occurred more frequently than 2000s, which seems to have caused excessively high salinity condition for habitation of C. japonica.
