安定同位体比およびC/N比から評価した

抄録

The total organic carbon (TOC), total nitrogen (TN), C/N ratio and carbon and nitrogen stable isotope ratio (δ¹³C and δ¹⁵N) of sedimentary organic matter (SOM) were measured to estimate the amount and source of surface SOM in Obama Bay, the central coast of Wakasa Bay. The concentration of TOC and TN of surface SOM in Obama Bay were

1.5–32.7 mg C・g^-1 and 0.2–2.4 mg N・g^-1, respectively. Spatial variations of TOC and TN in sediments were low in the western area. In contrast, they were higher in eastern area and dramatically increased at the mouth of the Kita and

Minami rivers. These maximum values of TOC and TN were similar to those of Osaka Bay which is known as a eutrophic sea area. The δ¹³C values and C/N ratio varied between -21.1‰ and -28.7‰, and 6.5 and 17.9 respectively. Judging from the δ¹³C and C/N ratio, the major origin of SOM in the western area was marine organic matter (mainly marine phytoplankton), whereas the major source of SOM in the eastern area was terrestrial organic matter (mainly terrestrial plants). These results are possibly related to the location of two main rivers, low flocculation in the estuaries

and counterclock-wise current in Obama Bay.