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Salt Water Behavior Near the Exit of Lake Ogawara, in Relation to the Breeding of Corbicula Japonica

Author(s): Tadaharu Ishikawa; Yasushi Tsuruta; Shuzo Nishida; Mai Narita

Linked Author(s): Tadaharu Ishikawa

Keywords: Seawater intrusion; Corbicula Japonica; Hydraulic environment for breeding; Field measurement; 3-D numerical flowsimulation

Abstract: Lake Ogawara is one of large brackish water lakes in Japan, in which the water living thing most predominant and important for fishery is Corbicula Japonica, a tiny clams commonly used for stock of Japanese miso soup. There is a mystery about the reproduction of the clams in the lake: The normal salinity concentration in the surface mixed layer is only 1 psu over the whole water area, which is far lower than the salinity needed for the breeding of the clams. On the other hand, an existing survey shows that the density of young clams is higher at shallow water area near the lake exit than other portion of the lake. From these evidences, authors have an assumption that Corbicula Japonica would breed mainly in a restricted area near the lake exit in a restricted period of seawater intrusion when the salinity increases briefly, and then larvae are transported and diffused over the lake by wind driven currents. In this study, the salt water behavior in the shallow water area near the lake exit in a period of salt water intrusion is investigated by field measurements and 3-D numerical flow simulation. The results show that the salinity condition favorable to the breeding of Corbicula Japonica is developed in a restricted period of time by a delicate dynamic balance of density current. The expectation of this condition, estimated on the basis of the statistical analysis of seawater intrusion to the lake, is considered to be frequent enough for the propagation of the clams.


Year: 2001

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