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.