Temporal Variability of Carbon and Nitrogen Stable Isotopes of Bivalves in Tamagawa River Estuary, Japan

Abstract

Temporal variability of carbon and nitrogen stable isotope ratios (δ13 C and δ15 N) in bivalves were investigated from May 2007 to February 2009 at two different stations in Tamagawa River estuary, Japan, together with chemical and isotopic compositions of potential food sources, such as suspended particulate matter and surface sediment. δ13 C and δ15 N in bivalves were enriched in the downstream station irrespective of the species. δ13 C and δ15 N of bivalves in both stations showed seasonal cycle, in which they were enriched in summer and depleted in winter. At both stations, remarkable decrease of clam δ13 C was observed after a high flood discharge, indicating strong influence of terrestrial organic matter inflow. In conclusion, it is revealed that δ13 C and δ15 N in bivalves are useful markers to trace time- integrated information of estuarine environments. 1.