Carbon and nitrogen sources for the bivalve Corbicula japonica in Natori River estimated from stable isotope analyses

We report measurements of the C and N stable isotope ratios (delta C-13 and delta N-15) in tissue of the bivalve Corbicula japonica and particulate organic matter (POM), and the C/N ratios of microalgae, terrestrial plants and sedimentary organic matter in Natori River, Miyagi Prefecture, Japan. delta C-13 of the bivalve and POM at upstream stations (4.0 similar to 4.5 km from the river mouth) were significantly lower than those in the downstream station (1.5 km from the river mouth). The low delta C-13 values in the upper two stations (between -28.0 and -25.5 parts per thousand) indicated that terrestrial organic matter is the primary C source of the bivalve. However, delta N-15 values for the bivalve at all stations (between 9.5 and 10.8 parts per thousand) did not differ significantly. This suggests that benthic microalgae are the primary N source in all stations. We conclude that C and N sources for the bivalve originate from different food items in the upper reaches of the river.