Model study of Lakes Shinji and Nakaumi — a coupled coastal lagoon system

To understand the physical and biological processes that occur in Lakes Shinji and Nakaumi, a coastal lagoon system, a hydrodynamic–ecological coupled model was applied. The model was run to hindcast these processes from March 1, 1995 to the end of September 1995. The simulation of physical processes suggests that the meteorologically induced sea level variation and a large episodic amount of freshwater discharge effectively caused the water exchange between the open sea and this lagoon system. The simulated results of the biological processes using the ecological model show good agreement with field data except for the phosphate concentration in the bottom water. It was also found that the microbiological processes in the water column, as well as in the sediment, contribute largely to the formation of oxygen-depleted water in the bottom layer. It was also clarified from the simulation that the two species of benthic bivalve, which have dense populations in this lagoon system, play important roles on removing organic particulate matter and nutrients from the system.