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Orcasphere » PCB bioaccumulation model for Puget Sound
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PCB bioaccumulation model for Puget Sound


Jeff Stern

Mapping C flow through the food web can help us understand trophic strucure and species interactions and ass feeding guilds and which species may be most at risk from bioaccumulation.  Our model is a steady state partitioning (Arnot and Gobas, 2004; Condon, 2007) that uses Tim Essingtons trophic structure data, diet data from John Ruem (2006 UW thesis), and other parameters from many others.  Essington’s data show that biomass and diet change dramatically with depth strata.

Our simplified model for the central basin of Puget Sound yields 9 out of 10 estimates for species or feeding guilds that are within factor of 2 of field measurements.  We have almost no data for plankton and spiny dog fish in the central basin.

Results:

  • For every unit you reduce water concentrations of PCBs, you get a 0.7 unit reduction in tissues; this is a linear response for all species; for 50% reduction in loading you get about 55 picograms/l in tissues.
  • The ratio for sediment conentrations of PCBs is 0.3; taking out all PS hot spots will reduce tissue concentrations by only about 15%.
  • These ratios vary by species (benthic, pelagic); eg English sole is most affected by sediment concentrations.  (Scott thot: SRKWs are known to eat Dover Sole in non-summer seasons…)
  • Even in most optimistic scenario, tissue reductions are only likely to be 15-25%.

Simplified food web structure seems to do well in approximating carbon flows, so we believe we are accurately modeling transfer of PCBs, generally.  You can add complexity to understand specific species’ situations.  We also believe you’ll need different simplified model for each basin in the Salish Sea.  That means we’ll need data from each basin!  And it means that we’ll need more complicated (trans-basin) models for species with complex foraging behaviors, like killer whales.

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