Using ratios of stable nitrogen and carbon isotopes to characterize the biomagnification of DDE, mirex, and PCB in a Lake Ontario pelagic food web

Abstract

Stable isotopes of nitrogen (δ 15 N) and carbon (δ 13 C) were used to describe the trophic status and interactions of biota characteristic of a Lake Ontario pelagic food web. Stable isotopes of nitrogen were further used to characterize the relationship between an organism's trophic position and the biomagnification of specific hydrophobic contaminants through this food web. The δ 15 N defines the relative trophic status as (i) the top predator, lake trout (Saivelinus namaycush); (ii) prey species, alewife (Alosa pseudoharengus), rainbow smelt (Osmerus mordax), and slimy sculpin (Cottus cognatus); (iii) macroinvertebrates, mysids (Mysis relicta), and amphipods (Diporeia hoyi); (iv) net zooplankton, dominated by cyclopoids (Diacyclops thomasi) and cladocerans (Bosmina longirostris); and (v) net phytoplankton, dominated by diatoms (Melosira spp.). The separation of the four fish species, lake trout and associated prey items (alewife, rainbow smelt, and slimy sculpin), on the basis of their mean δ 13 C signatures complements what is known about the preferred diet of these fishes. The enrichment of 15 N through this food web indicates that there is a strong correlation between the biomagnification of persistent lipophilic contaminants (p,p′-DDE, mirex, and PCB) and the relative trophic status of an organism as described by stable isotopes of nitrogen.