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

Abstract

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 δ13C varies among stream habitats, whereas Δ14C does not because Δ14C is corrected with δ13C, by definition. To test this hypothesis, we compared the variability of δ13C and Δ14C 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 δ13C values (from –31.9‰ to –16.3‰) were significantly different among the habitats whereas the Δ14C values (from –379‰ to –141‰) were not. Periphyton δ13C values depended on both algal photosynthetic activity and δ13C of the DIC, whereas periphyton Δ14C depended only on DIC Δ14C. The δ13C and Δ14C values of litter were constant. Thus, the difference between the periphyton and litter δ13C values (Δδ13C) varied among habitats, but their Δ14C differences (ΔΔ14C) did not. Our results indicate that Δ14C is spatially stable among stream habitats and that Δ14C measurements can be used to precisely determine carbon sources for stream food-web analysis within individual reaches.