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Nitrogen budgets and fauna of benthic organisms were examined at the pond of Osaka Nanko Bird Sanctuary, an artificial tidal flat of Hannan Second District and the natural tidal flat of Wakagawa estuary. These salt marsh and tidal flats, each locates at urban areas, are thought to be a typical ecosystem maintained by artificial environmental manipulation. The introduction of seawater to the salt marsh by sluice pipes and the conveyance of river water from inner tidal flat by pumps are effective methods to preserve the benthic ecosystems at Nanko Bird Sanctuary and Wakagawa Tidal Flat, respectively.

The purpose of this study is to evaluate effect of hypoxic water and blue tide on macrobenthos in artificial tidal flat, Omaehama in inner part of Osaka bay. Hypoxic water influences on macrobenthos to survive under to 1m water depth. In addition, it was revealed that bule tide influences on the amount of filtered water by Ruditapes philippinarum in DL±0m water depth. Blue tide decreased individual of R. philippinarum and the amount of filtered water by them. It is found that the creating artificial tidal flat enhances the number of R. philippinarum and filtaration, but occurrence of blue tide causes disappearance of purification function. These result indicated that it is necessary to consider the method for mitigation of blue tide impact when creating artificial tidal flat.

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