Natural carbon-14 signature provides new data for stream food web studies

Background/Question/Methods

In stream food web analysis, the contribution of carbon from periphyton (an autochthonous source) and terrestrial litter (an allochthonous source) are usually estimated by carbon stable isotopic (δ¹³C) difference. However, δ¹³C variability among stream local habitats often blurs the distinction of carbon sources in food webs. In stream biogeochemistry, the natural radiocarbon abundance (Δ¹⁴C) has been used to identify carbon turnover time in river ecosystems. It would also be an alternative method to identify carbon sources in stream food webs. Which is the better index for carbon sources, δ¹³C or Δ¹⁴C? Here, we compared the variability of δ¹³C and Δ¹⁴C of periphyton and dissolved inorganic carbon (DIC) in four habitats (open vs. shaded, riffle vs. pool) within a limestone-based stream reach.

Results/Conclusions

The δ¹³C values of periphyton (–31.9 ~ –16.3‰) were significantly different among the four habitats, while the Δ¹⁴C values (–379 ~ –141‰) were not. Canopy cover area and chlorophyll a concentration of periphyton have significant effects on periphyton δ¹³C but not on Δ¹⁴C. The δ¹³C and Δ¹⁴C values of DIC were not significantly different among the habitats. Periphyton δ¹³C values depended both on algal photosynthetic activity and the δ¹³C value of the inorganic carbon source (i.e., DIC), while periphyton Δ¹⁴C did not depend on algal photosynthesis but were dependent on DIC Δ¹⁴C. Both the δ¹³C and Δ¹⁴C values of litter were constant, and the difference between the periphyton and litter δ¹³C values (Δδ¹³C) varied among habitats, while their Δ¹⁴C values (ΔΔ¹⁴C) did not. The results implies that Δ¹⁴C is a better measure of periphyton and litter carbon than δ¹³C. Our results indicate that the Δ¹⁴C is spatially stable among stream habitats, and Δ¹⁴C measurements can be used to precisely determine carbon sources for stream food web analysis within individual reaches.