In coastal areas around big cities such as Tokyo Bay, intertidal flats decreased due to man-made reclamation lands constructions. Such a loss of tidal flats make, water quality environments deteriorated. In the study, we carried out field studies to estimate nutrient fluxes between inter tidal sediment and overlying water and intertidal water and neighbor sea water. In conclusion, we found the following results. (1) Function of this tidal flat is net source of phosphorus and net sink of nitrogen and chlorophyll-a in summer. And function of net source of phosphorus in summer changes to net sink of that in winter. (2)The fluxes of phosphorus and nitrogen from the intertidal sediment are 20% and 87% of the fluxes through the changes between tidal flat and neighbor sea water.