Persistent organic pollutants in benthic foodwebs
Abstract: Concentrations of persistent organic pollutants (POPs) in aquatic biota are dependent on several factors both on individual and on system level. Bioaccumulation of POPs in pelagic biota in lakes as well as fish in streams has been shown to be dependent on nutrient regime of the system. In lakes, POP concentrations in pelagic biota decrease with increasing lake trophy. In this thesis POP bioaccumulation in benthic biota in lakes were investigated. In profundal chironomids POP concentrations decreased with increasing lake trophy while concentration were independent of lake trophy in littoral signal crayfish (Pacifastacus leniusculus). Chironomids feed on settling pelagic phytoplankton while crayfish feeding are influenced by terrestrial input. In streams, PCB concentrations in crayfish were independent of nutrient regime. In earlier studies POP concentrations in stream living trout has been shown to increase with increasing nutrient regime. Trout are highly dependent on autotrophic energy while crayfish diet is influenced by terrestrial sources. No difference in POP concentrations in lake and stream living crayfish could be found but the variation were higher in streams. The more dynamic properties of streams compared to lakes are probably reflected in crayfish POP concentrations. In New Zealand, POP concentrations in Longfinned eels (Anguilla dieffenbachii) were investigated. Concentrations of POPs were low compared to other studies on eels. The low levels were explained with low atmospheric deposition due to local geographical conditions and few point sources. In crayfish no effect of age and lipid content could be found as been shown for fish. Crayfish has, contrary to fish, continuous moulting events and normally change shell at least once a year. Moulting is energy demanding and means a total utilization of energy stores like those containing lipids. POPs can then be fully or partially eliminated and the process creates a cycle of POP accumulation that occurs between moulting events- not over whole life span as in fish. Diet and bioaccumulation of POPs in crayfish were affected by intrapopulation parameters. Crayfish populations in some lakes were size segregated and larger crayfish were found in shallow areas of the littoral zone. Further, larger crayfish were feeding at a higher trophic level and had higher levels of POPs. We hypothesize that a combination of predation pressure, habitat availability and intraspecicfic interactions influence population distribution with following size dependent shifts in diet that influence the uptake of POPs in crayfish.
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