Combined use of radiocarbon and stable carbon isotopes for the source mixing model in a stream food web

Naoto F. Ishikawa, Jacques C. Finlay, Hiromi Uno, Nanako O. Ogawa, Naohiko Ohkouchi, Ichiro Tayasu, Mary E. Power

Research output: Contribution to journalArticlepeer-review

Abstract

Radiocarbon natural abundance (Δ14C) has emerged as a useful dietary tracer in freshwater ecology for the past decade, yet its applicability for separating aquatic and terrestrial resources has not been examined quantitatively. Here, we report Δ14C values of stream invertebrates in different functional feeding groups collected from the upper South Fork Eel River watershed, northern California. We found that algae-grazing insect larvae show low Δ14C values (−43.1 ± 21.8‰, mean ± standard deviation, N = 6), reflecting the signal of dissolved inorganic carbon weathered from ancient inorganic carbon or respiration of old organic carbon. In contrast, the Δ14C values of leaf-shredding insect larvae (21.7 ± 31.9‰, N = 5) were close to those of contemporary atmospheric CO2 except at the SF Eel River where algal production was highest. The Δ14C values of predators (−6.1 ± 35.7‰, N = 14) were intermediate between those of grazers and shredders. In a Bayesian mixing model, Δ14C provided a more ecologically realistic estimate for terrestrial vs. aquatic source contributions to invertebrates with lower uncertainty (i.e., narrower credible interval) than did the stable carbon isotopes (δ13C). These results demonstrate that Δ14C can be used, in combination with δ13C, to more precisely estimate organic matter sources to stream animals.

Original languageEnglish (US)
Pages (from-to)2688-2696
Number of pages9
JournalLimnology and Oceanography
Volume65
Issue number11
DOIs
StatePublished - Nov 2020

Bibliographical note

Funding Information:
We thank Bob Hall and two anonymous reviewers for providing valuable comments on the manuscript, and Collin A. Bode for providing the field map. We also thank the Steel‐Angelo families and the UC Natural Reserve System for providing the Angelo Coast Range Reserve as a protected site for this research. This study was supported by the River Fund (Grant 25‐1215‐023 and 25‐1263‐017) and the KAKENHI Grant (18H02513). N.F.I. was a postdoctoral research fellow of Japan Society for the Promotion of Science (25‐1021). M.E.P. was supported by the Eel River Critical Zone Observatory NSF CZP EAR‐1331940 and by the National Center for Earth surface Dynamics, NSF Cooperative Agreement EAR‐0120914.

Funding Information:
We thank Bob Hall and two anonymous reviewers for providing valuable comments on the manuscript, and Collin A. Bode for providing the field map. We also thank the Steel-Angelo families and the UC Natural Reserve System for providing the Angelo Coast Range Reserve as a protected site for this research. This study was supported by the River Fund (Grant 25-1215-023 and 25-1263-017) and the KAKENHI Grant (18H02513). N.F.I. was a postdoctoral research fellow of Japan Society for the Promotion of Science (25-1021). M.E.P. was supported by the Eel River Critical Zone Observatory NSF CZP EAR-1331940 and by the National Center for Earth surface Dynamics, NSF Cooperative Agreement EAR-0120914.

Publisher Copyright:
© 2020 Association for the Sciences of Limnology and Oceanography

Copyright:
Copyright 2020 Elsevier B.V., All rights reserved.

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