Study on the controlling factors to construct tidal flat ecosystem having similar characteristics to natural tidal flat.

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The objective of this study is to identify the controlling factors to tidal flat ecosystem having similar characteristics to natural tidal flat ecosystem. Specific conclusions derived from this study are as follows :(1)When the slope of the restored tidal flat was small and soil with high content of silt and bacterial population was used, constructed tidal flat similar to natural tidal flat was temporarily created. However, the slope of the tidal flat increased again and the silt content and bacterial population also decreased after two years of the restoration. It is suppose that if techniques for the maintenance and management like making a breakwater are not applied to the restored tidal flat, washout of tidal flat soil occurs gradually because of daily seawater flow even if a constructed tidal flat similar to the nature was created.(2)The silt and organic carbon contents in low- and high-submerged-breakwater zone were higher than those in the no-submerged-breakwater zone. The slope … More s, reduction zone and permeability of sediment in the submerged breakwater zones were almost the same as those in natural tidal flats at Hiroshima Bay(3)The total population density of macrobenthos in the low- and high-submerged-breakwater zone were about twice as high as that in the no-submerged-breakwater zone. The dominant macrobenthic species in the submerged breakwater zones were Ceratoneres erthraeenesis and Mediomastus sp., which are common in natural tidal flats at Hiroshima Bay.(4)Tidal flat sediments of silt content 5-40% (the silt source : dredging soil) were placed in tidal flat simulator. After one month, these tidal flat simulator were operated for 2 weeks under the same tide cycle (12h) and wave (5cm) condition. The silt content rate of each tidal flat was almost same.(5)The constructed tidal flat sediment (silt content 25%) using dredging soil as silt source and the natural tidal flat sediment (silt content rate 25%) were placed in the tidal flat simulator. It was clarify the effects of dredging soil to organic purification and macrobentos ecosystem on tidal flat. The dredging soil system for organic purification was decreased to about 1/2 the natural sediment system. However, the dredging soil was not decrease to he natural sediment system. Less