Spatial modification of a food web model simulating PCBs transfer in the
Detroit River
Zhicai Liu
Definitions
Food web: it is the network of feeding interactions in the ecosystem, with species as the nodes that are
linked when one feeds on the other.
Biomagnification: cumulative increase in the concentration of a chemical in successively higher trophic
levels generally as a result of predation.
PCBs: a class of persistent and highly accumulative organic pollutants, which can exhibit a wide range
of toxic effects on the health of fish, wildlife and humans, and are probably carcinogenic to humans.
Fish consumption advisories: government health advice issued to the public concerning deleterious
substances in fish and/or shellfish (e.g., crabs). These advisories typically provide advice on avoiding or
limiting the consumption of certain types, sizes, or parts of fish, or on the number of fish meals to
consume over a period of time in order to limit health risks.
Research Objective
The objective of this study is to improve our understanding of factors controlling PCB transferred to fish
through incorporating spatially connected information of PCB concentrations in sediment and water and
feeding interactions.
Background
- A simulation model of the Detroit River food web was developed to estimate the PCB concentrations
in fish, where the food web contained 36 taxonomic groups (Morrison et al. 1997).
- The aquatic organisms (phytoplankton, zooplankton, invertebrates, and fish) are exposed to PCBs in
river water and sediment, and the PCBs are transferred in complex food web system (Nfon et al. 2008;
Rashleigh et al. 2009).
Paper view
Paper 1: Ecological food web analysis for chemical risk assessment
- Importance of food web analysis for chemical risk assessment: 1. simulated pathways of materials
and energy flow based on the trophic interactions; 2. understand effects of contaminants at a
community or ecosystem level; 3. identify cascades of indirect effects.
- Steps in food web anaysis and modeling: 1. develop food web modeling objectives; 2. develop
graphic food web models; 3. define spatial-temporal scale and resolution; 4. characterize diet
composition in space and time; 5. characterize chemical uptake and trophic transfer processes; 6.
construct, calibrate and validate quantitative food web models.
- Case study – aquatic food web analysis for the Upper Hudson River: the dietary composition of the
target fish species varies substantially with habitat type and river sampling area, as well as with season.
Paper 2: Role of chemical and ecological factors in trophic transfer of organic chemicals in aquatic
food webs
- This study investigated the trophic transfer of organic contaminants in an aquatic community
composed of zooplankton, benthic invertebrates, and fish.
- The findings illustrated that: feeding relationships play an important role in controlling the exposure of
chemicals in food webs.
Paper 3: A river-wide survey of PCBs, PAHs, and selected organochlorine pesticide residues in
sediments of the Detroit River – 1999
- This survey employed a stratified random sampling design that divided the river into six geostatistical
zones consisting of upper, middle, and lower U.S. and equivalent Canadian river reaches.
- This study found that the total PCB concentrations were significantly elevated at sample stations of
U.S. side as compared to Canadian stations, where the sediment PCB concentrations in the upper and
middle U.S. river are lower than those in the lower reach.
Theoretical foundation and discrepancy
- Spatial variation in food web structure has been ignored (Rooney et al. 2008). In consideration to
spatial dimension of PCB uptake and transfer, the spatial variability of PCB loadings and feeding
interactions are critical.
- Spatial variability of PCB concentrations in sediment and water were not incorporated in the preexisting Detroit River food web model.
Research questions
- Does the spatially modified model improve site-specific predictions of PCB concentrations in fish?
- Does the pattern of PCB concentrations in fish reveal their movement distances and PCB loadings in
their home zones?
Practical significance of spatial variability of PCBs concentrations in PCB intake
- Spatial distribution patterns of PCB accumulation in spottail shiners (Suns et al. 1993), burrowing
mayfly (Corkum et al. 1997), zebra mussels (Metcalfe et al. 1997), and snapping turtles (de Solla and
Fernie 2004) have demonstrated the site-specific bioavailability of PCB inputs at different locations of
Detroit River and other Lake Erie areas.
- A series of model research on food web bioaccumulation have predicted that the PCB
concentrations in fish are very sensitive to the PCB concentrations in sediments (Suns et al. 1993;
Morrison et al. 1997; Gewurtz et al. 2009).
- Significant spatial pattern of PCB loading in the Detroit River was demonstrated in Drouillard et al.
(2006). PCB loading in the sediment is the original driving force of PCB accumulation in the aquatic
organisms.
Practical significance of movements of organisms in PCB transfer
- Similar to the role of fish movement as a nutrient or energy transport systems in river ecosystems
(Polis et al. 1997; Woodward and Hildrew, 2002), the movements of organisms (particularly fish) play
an important role in PCB transport across local food webs.
- The species with short movement distances are exposed to the constant PCB concentration present
in their small ranges, while the more mobile predators are exposed to a large gradient of PCB
concentrations and couple the pathways of PCB transfer because they forage a large home range.
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