Quantification of Purification Ability for Organic Matter at Natural and Constructed Tidal Flats and the Role for Purification in Hiroshima Bay.

The objective of this study is to estimate the purification capacity for organic matter (carbon) in natural and man-made tidal flats. In this study, we measured respiration rates and biomass for diatom+bacteria+meiobenthos and macrobenthos in the permeable layer of soil in tidal flats. Furthermore, the role of these tidal flats for the purification of organic matter in Hiroshima Bay was studied.The man-made tidal flats had deeper permeable layer for purification of sea water compared to the natural tidal flats. The carbon biomass of bacteria and macrobenthos were not significantly different between the natural and the man-made tidal flats. The respiration rates by diatom+bacteria+ meiobenthos and macrobenthos were not significantly different between the natural and the man-made tidal flats. However, the purification capacity by diatom+bacteria+meiobenthos and macrobenthos in man-made tidal flats was higher than that in natural ones. It is most probable that permeable layer of soil for purification capacity in man-made tidal flats was deeper compared to the natural ones. Purification capacity of natural and man-made tidal flats was compared with external and internal organic loading into Hiroshima Bay. The percent contribution of tidal flats was only about 0.5n%. Even if there were restoration of the area as in 1940s, the constribution will be 1.6%. The purification capacity of organic matter in tidal flats is not large as expected compared with pollution loading in Hiroshima Bay.