Sulfur stable isotope signature identifies the source of reduced sulfur in benthic communities in macrophyte zones of Lake Biwa, Japan

Abstract

Carbon, nitrogen and sulfur stable isotope ratios (δ13C, δ15N and δ34S) were measured from water column sulfate, sediments, particulate organic matter (POM), macrophytes, periphyton, macroinvertebrates and fish, sampled from the littoral, open water and macrophyte zones of Lake Biwa. In most of the littoral zones, the δ13C and δ15N values of organisms indicated that POM and periphyton support the consumers. However, in the dysoxic interior macrophyte (IM) zone, the δ13C values of Sinotaia quadrata histrica, Propsilocerus akamusi and Anodonta woodiana were lower than that of all resources. The δ15N values of S. quadrata histrica were lower than those of P. akamusi and A. woodiana. δ13C and δ15N values thus failed to distinguish the foods of these consumers. The δ34S values of sediment and S. quadrata histrica were lower than those of water column sulfate, suggesting that this consumer incorporated reduced sulfur derived from sulfate reduction in the sediment by ingesting detritus. In contrast, the δ34S values of P. akamusi and A. woodiana were higher than that of S. quadrata histrica, suggesting that they incorporated sulfur derived from water column sulfate by ingesting POM. Consequently, δ13C, δ15N and δ34S signatures provide complementary estimates of foods for consumers in this freshwater lake.