Appendix C. Diel δ13C-DIC data from Pick Creek before and after salmon spawning.
|(a) Diel dissolved inorganic carbon isotope ratios (δ13C-DIC) for Pick Creek from 5 sampling periods. Two sampling periods were before salmon entered the stream (28–30 Jun & 14–15 Jul, 2008) and three were after salmon (18–20 Aug, 29–31 Aug, 4–5 Sept, 2008). Filled symbols indicate samples taken at night. Prior to salmon there is enrichment of DIC during the day due to photosynthetic uptake of CO2 by aquatic algae, which strongly favors the light isotope. This diel enrichment signal is nearly removed at peak spawning (18–20 Aug), indicating greatly reduced GPP, and partially recovers as the salmon run declines.|
(b) Mean nighttime δ13C-DIC ± 1 SD from data presented in panel a. Salmon are enriched in δ13C (-21 ± 1‰, Johnson and Schindler 2009) relative to both terrestrial vegetation (~-27 ± 3‰) and periphyton (-36 ± 3‰, unpublished data). The trend for enrichment in δ13C-DIC supports modeling results which suggest the contribution of salmon metabolism to total ecosystem respiration increases as the run progresses. Values are more enriched than the salmon end-member because of reaeration with the atmosphere (~-8‰).
Johnson, S. P. and D. E. Schindler. 2009. Trophic ecology of Pacific salmon (Oncorhynchus spp.) in the ocean: a synthesis of stable isotope research. Ecological Research 24:855–863.
Peterson, B. J. and B. Fry. 1987. Stable isotopes in ecosystem studies. Annual Review of Ecology and Systematics 18:293–320.