Tidal flats provide the function of water quality improvement by removing nutrients from the water. The aim of this study is to measure the role of tidal flat on water quality improvement in the Tokyo Port Wild Bird Park. Results from the field measurement show that (1) the tidal flat has a role of a source of the phosphorus and a sink of the nitrogen in summer, but a sink of the nitrogen and phosphorus in winter, (2) the tidal flat adsorbed of NO3- into the sediment and the release of PO4+3 to the overlying water in both summer and winter, (3) the amount of removed nutrients by water birds is negative due to their excrement when the feeding rate is assumed as the rate of feeding action. (4) Denitrification and anammox formed in the sediment are thought to be major factors explaining the nitrogen removal by the tidal flat sediment.
