Thursday, May 29, 2008 - 4:00 PM
612

The influence of temporal variability in algal carbon stable isotope signatures on stream food web interpretation and analysis

Wade L. Hadwen, Mark Spears, and Mark J. Kennard. Australian Rivers Institute, Griffith University, Griffith School of Environment, Nathan, Queensland, Australia 4111, Brisbane, Australia

Variability in the δ13C signatures of primary carbon sources can strongly influence the accuracy of stable isotope food web analyses. We examined the temporal variability of δ13C signatures of benthic algae over an 8 week period in five streams in southeast Queensland, Australia. Week-to-week variation in benthic algal δ13C signatures was largely driven by changes in flow at each site, although the direction and magnitude of change were not consistent across sites. Algal signature variability had a substantial effect on consumer diets analysed using Isosource mixing model software, with differences in contributions of algal carbon of up to 11% between weeks. More importantly, we found many occasions in which the δ13C signatures of some consumers sat beyond the range of available sources, meaning the mixing model did not have a valid solution. Together, these findings suggest that temporal variability in algal δ13C signatures can strongly influence food web interpretations and the applicability of mixing model analyses. We recommend that future food web studies incorporate assessment of the temporal variability in source signatures in a period prior to consumer organism sampling , to better characterise end member signatures and their relevance to consumers at the time of capture.


Web Page: organic matter, autochthonous, algal variability

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