A new application of radiocarbon (14C) concentrations to stream food web analysis

We measured radiocarbon concentrations (Δ14C), together with stable isotope ratios (δ13C and δ15N) of aquatic animals, periphytic algae and particulate organic matter (POM) at upstream sites of two streams. We hypothesized that Δ14C values of organisms would be separated into two major carbon sources in streams: in-stream production (autochthonous production) and terrestrial detritus (allochthonous production). In fact, Δ14C values of in-stream production were low, while those of terrestrial detritus were high. This indicates the difference in sources: the former reflects the Δ14C values of the dissolved inorganic carbon in the catchment, whereas the latter reflects the Δ14C value of present atmospheric CO2. Δ14C patterns of animals differed in each of the two streams, suggesting that the role of food web structure is critical for understanding the carbon dynamics of stream ecosystems. We present, for the first time, the potential use of radiocarbon (14C) in the study of food webs in stream ecosystems.