Food-web components of a Lake Superior coastal wetland and adjacent offshore waters were examined with stable isotope ratio techniques for carbon and nitrogen. We found distinct carbon isotope ratio signatures for organisms collected in the wetland and from offshore. Both food-web groups seemed to be based on carbon fixed by phytoplankton.Compared to offshore organisms, the wetland food web was depleted in 13C. We found the nitrogen isotope ratio signatures to be enriched in "N by -3% at each succeeding trophic level in both wetland and lake samples. No evidence of a direct energ! link between the abundant macrophyte biomass in the wetland and the fisheries food web was found. The carbon ratio of rainbow smelt (Osmerus mordux) and walleye (Stizostedion vitreum) exhibited a shift from a wetland signature in young-of-the-year to an offshore signature in juveniles and adults. Yellow perch (Percaflavescens) young-of-the-year exhibited a planktivorous 615N signature, while adults were enriched in 15N. Both examples illustrate the utility of stable isotope ratio techniques in confirming feeding shifts associate,d with growth and habitat change.
Stable‐isotope ratio signatures of primary producers in a coastal wetland and in adjacent offshore waters of western Lake Superior indicated that phytoplankton are the primary source of carbon for the grazing food web of this ecosystem. This study outlines the possible roles of other autotrophs in this regard. Isotopic signatures of macrophytes reflected their life‐form‐associated constraints on diffusion of inorganic carbon. Data indicated that differences between wetland and lake phytoplankton may be explained by the isotopic signatures of their dissolved inorganic carbon (DIC) sources. Results of an in situ experiment showed that respiration associated with macrophyte decomposition is capable of enriching surrounding water with significant amounts of 13C‐depleted DIC and lowering the net δ13C ratio of DIC in water in lowturbulence situations. The δ13C ratio for wetland phytoplankton may be depleted relative to pelagic algae because the fixed carbon is derived from decomposing detritus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.