The objective of this study is to evaluate the role of tidal action and benthic animals such as seaworm in denitrification activities of the tidal flat in Tamagawa river through the field investigation. It was regularly observed that only NO3-N concentrations in interstitial water in surface layers of the tidal flat sediment changed with a high-low tidal action. The 24-hour survey showed that the changes in NO3-N concentrations in interstitial water were observed regularly through the tidal action cycle. Based on the tidal action-dependent decrease of NO3-N concentrations, denitrification rates were calculated. The apparent denitrification rates show that (i) water temperature, (ii) NO3-N concentrations in surface water, (iii) tidal level difference between high- and low-tides, and (iv) existence of benthic animal's burrow affect denitrification activity of the tidal flat sediment.
