USING RATIOS OF STABLE NITROGEN AND CARBON ISOTOPES TO CHARACTERIZE THE BIOMAGNIFICATION OF DDE, MIREX, AND PCB IN A LAKE-ONTARIO PELAGIC FOOD-WEB

Stable isotopes of nitrogen (delta(15)N) and carbon (delta(13)C) were used to describe the trophic status and interactions of biota characte ristic of a Lake Ontario pelagic food web. Stable isotopes of nitrogen were further used to characterize the relationship between an organis m's trophic position and the biomagnification of specific hydrophobic contaminants through this food web. The delta(15)N defines the relativ e trophic status as (i) the top predator, lake trout (Salvelinus namay cush); (ii) prey species, alewife (Alosa pseudoharengus), rainbow smel t (Osmerus mordax), and slimy sculpin (Cottus cognatus); (iii) macroin vertebrates, mysids (Mysis relicta), and amphipods (Diporeia hoyi); (i v) net zooplankton, dominated by cyclopoids (Diacyclops thomasi) and c ladocerans (Bosmina longirostris); and (v) net phytoplankton, dominate d by diatoms (Melosira spp.). The separation of the four fish species, lake trout and associated prey items (alewife, rainbow smelt, and sli my sculpin), on the basis of their mean delta(13)C signatures compleme nts what is known about the preferred diet of these fishes. The enrich ment of N-15 through this food web indicates that there is a strong co rrelation between the biomagnification of persistent lipophilic contam inants (p,p'-DDE, mirex, and PCB) and the relative trophic status of a n organism as described by stable isotopes of nitrogen.