1The United Graduate School of Agricultural Science, Ehime University, Kita, Kagawa 761- 0795, 2Department of Life Science, Kagawa University, Kita, Kagawa 761- 0795, 3Toyota Yahagi River Institute, Toyota, Aichi 471- 0025, 4Faculty of Environmental and Symbiotic Science, Prefectural University of Kumamoto, Tsukide, Kumamoto 863- 8502, Japan
The total organic carbon (TOC) content and the carbon stable isotope ratio (δ13C) of Chita Bay surface sediments were measured to investigate the organic matter content and origin. Judging from the δ13C, the TOC content of the sediments at the western and central parts of Chita Bay were high due to the organic matter originating in the coastal sea. However, we found a large variation in the TOC content and the δ13C in the Yahagi River mouth sediments, which suggested that surface sediment organic matter in these areas had different sources from land or coastal sea. Particularly, at the western and central part of the Yahagi River mouth, the TOC content of the sediments was high, and the surface sediment was composed largely of terrestrial organic matter and smaller size particles (250 μm). These facts suggest that many small particles and organic matter from the Yahagi River will affect the sediment chemical environmental condition in the Yahagi River mouth.