Stable isotope technique for evaluation of organic matter movement and coastal environment status

Stable carbon and nitrogen isotope techniques were used to clarify the movement of terrestrial organic matter and the status of coastal environment of the Osaka Day which was known as one of the most polluted coastal areas in Japan. Sedimental cores and particulate matter samples from the Yodo River and the Osaka Day were collected for examination of delta(13)C, delta(15)N, carbon and nitrogen contents. Means delta(13)C for sediment, large size of particulate organic matter (15-149 mu m) and small size of particulate organic matter (<15 mu m) in the Yodo River were -25.1+/-0.2 parts per thousand, -25.3+/-0.6 parts per thousand and -25.5+/-0.4 parts per thousand, respectively, whereas means of those the inner part of the Osaka Day were -20.6+/-0.3 parts per thousand, -21.6+/-1.6 parts per thousand and -22.3+/-1.7 parts per thousand, respectively. In the outer part of the Osaka Day, mean delta(13)C for large size of particulate organic matter (-20.7+/-0.9 parts per thousand) was slightly increased, but for small size of particulate organic matter (-22.5+/-1.3 parts per thousand) was nearly similar to those in the inner part. Our results suggest that the sediments in this coastal area were mostly derived from primary production in the bay. Almost of the large particle of terrestrial organic matter discharged from the Yodo River into the Osaka Bay had been deposited onto the bottom sediment at the inner part, within a few kilometers close to the river mouth, while the small particle of terrestrial organic matter was more transported through the bay to neighbor sea areas. Nitrogen sources as nutrients for phytoplankton growth in each area of the bay may be different since the values of delta(15)N for sediment, large and small size of particulate organic matters significantly varied. Such nutrients should be great contributed from marine origin.