Natural C-14 provides new data for stream food-web studies: a comparison with C-13 in multiple stream habitats

In stream food-web analysis, the contributions of carbon from periphyton (an autochthonous source) and terrestrial litter (an allochthonous source) are estimated by isotopic difference. We hypothesised that periphyton delta C-13 varies among stream habitats, whereas Delta C-14 does not because Delta C-14 is corrected with delta C-13, by definition. To test this hypothesis, we compared the variability of delta C-13 and Delta C-14 of periphyton and dissolved inorganic carbon (DIC) in four habitats (open v. shaded, riffle v. pool) within a limestone-based upland stream in Japan. Periphyton delta C-13 values (from -31.9% to -16.3%) were significantly different among the habitats whereas the Delta C-14 values (from -379% to -141%) were not. Periphyton delta C-13 values depended on both algal photosynthetic activity and delta C-13 of the DIC, whereas periphyton Delta C-14 depended only on DIC Delta C-14. The delta C-13 and Delta C-14 values of litter were constant. Thus, the difference between the periphyton and litter delta C-13 values (Delta delta C-13) varied among habitats, but their Delta C-14 differences (Delta Delta C-14) did not. Our results indicate that Delta C-14 is spatially stable among stream habitats and that Delta C-14 measurements can be used to precisely determine carbon sources for stream food-web analysis within individual reaches.