Abstract
Living things play unique and important roles in material circulations in a rural area. Their abilities seem to get weak after land improvement.
This study consists of four examinations, using stable isotope ratio. The first one examined nitrogen transfer into living world by periphyton. The second one attempted to analysis the foodweb in Habahiro suiro canal. Detritus is principal producer like algae. The third one showed an area of distribution of stoney (Sterwpsyche sp.) and nitrogen restoration to terristrial area with the invertebrate. The last one made clear that nitrogen derived from farm house drainage was absorbed by Reed Canary grass (Phragmites australis).
These results suggested that not only preservation of continuity in aquatic area, but also various bottom materials and water velocity were essential measures to promote material circulations by living things.
