Abstract
The origin and bacterial utilization of organic matters in tidal-flat sediment were investigated using stable isotope and fatty acid analysis. Sedimentary organic matter (SOM) and potential food sources such as land plant, marine particulate organic matter (POM), benthic microalgae, riverine POM were taken from Gamo lagoon and Nanakita River Mouth. Land plant (δ13C = －26.6 and δ15N = 3.6) and riverine POM (δ13C = －25.5 and δ15N = 8.9) were isotopically distinct from benthic microalgae (δ13C = －16.3 and δ15N = 6.2) and marine POM (δ13C = －20.3 and δ15N = 10.3). In the degradation experiment of SOM for 50 days, the δ13C value of SOM decreased from －19.1 ‰ to －20.7 ‰. This was due to the preferential utilization of higher δ13C organic matter such as benthic microalgae and marine POM by bacteria. Land plant and riverine POM had begun to degrade after the degradation of benthic microalgae and marine POM progressed.
