地水環境学

In brackish lakes undergoing artificial salinity management, the demonstrating countermeasure scenarios for optimum salinity management is crucial for protecting water environment and increasing the production of water resources. Arming at the fundamental research on this issue, the authors constructed a two-dimensional numerical model that utilized Alternative Direction Implicit method (ADI) to examine lake currents and salinity dispersion. We applied this model to Lake Togo in Tottori Prefecture, Japan, and investigated the effect of wind speed and its direction on the flow pattern of wind-driven currents, and the effects of river discharge, wind speed and its direction on the spatial distribution of wind-diffused salinity. When we modeled river discharge using a sine-curve with an amplitude of 4.0 m^3/s and a cycle of 12 hours, the salinity in the northwest and northeast areas fluctuated in the range of 4～12 psu. In the southwest and southeast areas, it fluctuated in the range of 6～8 psu. The result indicated that an approximate discharge of 4.0 m^3/s is needed to maintain the optimum salinity of level in Lake Togo during the breeding season of Yamato-shijimi (Corbicula japonica PRIME). The horizontal distribution of wind-driven currents in the northwest area in the cases of north and south winds was the same direction as the wind; in the northeast area, it was the opposite direction of the wind. The southwest area had clockwise currents under the north wind and counterclockwise currents under the south wind. The southeast area had very weak currents in the cases of north and south winds. Comparing the southwest and southeast areas, it was concluded that the pattern of wind-driven currents are connected to the environment of the bottom sediments and the habitat area of Yamato-shijimi.