Bull. Jpn. Soc. Fish. Oceanogr. 71(1), Page 18-28, 2007   Verification of a technique to quantify the water purification function of a macrobenthic community using a tidal flat experimental facility Kazuya Takeda1†, Motoo Ishida2, Hiroaki Aoyama2 and Teruaki Suzuki3 1 Aichi Chita Office of Agriculture, Forestry and Fisheries, 1-36 Deguchi-cho, Handa, Aichi 475-0903, Japan 2 Aichi Fisheries Research Institute, 97 Wakamiya, Miya-cho, Gamagori, Aichi 443-0021 Japan 3 Marine Resources Research Center, Aichi Fisheries Research Institute, 2-1 Toyohama, Minamichita-cho, Aichi 470-3412, Japan †e-mail: kazuya_takeda@pref.aichi.lg.jp In order to quantify the water purification function of a macrobenthic community, the concentrations of nutrients in overlying water were monitored hourly using the tidal flat experimental facility at Aichi Fisheries Research Institute, which reproduced physical environmental conditions such as tidal level, tidal currents, waves, and winds. The experimental ecosystem supported a macrobenthic community dominated by bivalves. All the nutrient elements (NH4-N, NO2-N, DON (dissolved organic nitrogen), PON (particulate organic nitrogen), PO4-P, and DOP (dissolved organic phosphorus)) except for NO3-N in the water column were removed. The calculated removal rate of PON by the macrobenthic community (50 mg N·m-2·day-1) was found to be similar to that estimated by an alternative simple index, or PONrm (41 mg N·m-2·day-1), which had been devised based on the biomass of the macrobenthic community, and standing stock of chlorophyll a and pheo-pigment in an earlier study conducted by our research group. This finding suggests that PONrm is a simple and proper index for quantifying the water purification function of macrobenthic communities. Key words: tidal flat, mesocosm, particulate organic nitrogen, water purification, macrobenthos