Abstract
The objective of this study is to clarify food sources of benthic community and estimate the origin of sedimentary organic matter using carbon and nitrogen stable isotope ratios in two tidal flats of river mouth. The δ13C value of sediments around reed community is lower in the upstream section, but is higher in the downstream section in both tidal flats. Contribution of terrestrial organic matter in the downstream section of the tidal flats was lower than that in the upstream section. Although benthic consumers were distributed in the stations with sediment containing terrestrial organic matter, they did not assimilate terrestrial organic matter as their food sources. Moreover, benthic consumers have selectively assimilated food sources supplied from water column. The δ13C value and contribution of terrestrial organic matter of sediment showed statistically significant differences among the groups of stations distinguished according to cluster analysis for particle size composition and difference in elevation. Benthic consumers mainly assimilating MPOM and benthic diatoms as their food sources, however, were distributed in the stations of sediment groups with rich terrestrial organic matter. These results implied that food sources of benthic community did not correspond to sediment characteristics in the tidal flats of river mouth.
