Mercury Cycling in Stream Ecosystems. 3. Trophic Dynamics and Methylmercury Bioaccumulation

U.S. Geological Survey, Florida Integrated Science Center, 2639 North Monroe Street, Suite A-200, Tallahassee, Florida 32303, USA.
Environmental Science and Technology (Impact Factor: 5.33). 05/2009; 43(8):2733-9. DOI: 10.1021/es8027567
Source: PubMed


Trophic dynamics (community composition and feeding relationships) have been identified as important drivers of methylmercury (MeHg) bioaccumulation in lakes, reservoirs, and marine ecosystems. The relative importance of trophic dynamics and geochemical controls on MeHg bioaccumulation in streams, however, remains poorly characterized. MeHg bioaccumulation was evaluated in eight stream ecosystems across the United States (Oregon, Wisconsin, and Florida) spanning large ranges in climate, landscape characteristics, atmospheric Hg deposition, and stream chemistry. Across all geographic regions and all streams, concentrations of total Hg (THg) in top predator fish and forage fish, and MeHg in invertebrates, were strongly positively correlated to concentrations of filtered THg (FTHg), filtered MeHg (FMeHg), and dissolved organic carbon (DOC); to DOC complexity (as measured by specific ultraviolet absorbance); and to percent wetland in the stream basins. Correlations were strongest for nonurban streams. Although regressions of log[Hg] versus delta15N indicate that Hg in biota increased significantly with increasing trophic position within seven of eight individual streams, Hg concentrations in top predator fish (including cutthroat, rainbow, and brown trout; green sunfish; and largemouth bass) were not strongly influenced by differences in relative trophic position. Slopes of log[Hg] versus delta15N, an indicator of the efficiency of trophic enrichment, ranged from 0.14 to 0.27 for all streams. These data suggest that, across the large ranges in FTHg (0.14-14.2 ng L(-1)), FMeHg (0.023-1.03 ng L(-1)), and DOC (0.50-61.0 mg L(-1)) found in this study, Hg contamination in top predatorfish in streams likely is dominated by the amount of MeHg available for uptake at the base of the food web rather than by differences in the trophic position of top predator fish.

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    • "Owing to the biomagnification of mercury and the general correlation between d 15 N values and trophic level (Jardine et al., 2006), stable isotope analysis can be a useful tool for comparing mercury concentrations among sympatric species in marine and aquatic food webs (Chasar et al., 2009; Brasso et al., 2012; Day et al., 2012; Carravieri et al., 2013). However, d 15 N values cannot be directly compared among geographically distinct food webs as temporal and spatial variation in primary productivity, latitude, and ocean frontal region results in geographic differences in baseline d 15 N values (Post, 2002; McMahon et al., 2013). "
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    • "Fish trophic positions were estimated from d 15 N that was adjusted (Kidd et al., 1995; Anderson and Cabana, 2007) for siteto-site variation in basal d 15 N by subtracting mean d 15 N from periphyton samples collected from selected habitats at each site, as described elsewhere (Bell and Scudder, 2004, 2007; Beaulieu et al., 2012; Riva-Murray et al., 2013b, 2013c). Periphyton was used instead of a common lowest trophic-level consumer (Chasar et al., 2009), because no single primary consumer species/feeding guild was available across all sites (Beaulieu et al., 2012; Riva- Murray et al., 2013b). Axial muscle tissue was analyzed for total "
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    • "It can also reveal differences in mercury's basal concentration as it enters the food web as a result of differences in its availability (i.e., due to loading or bioavailability). FWMFs have been reported for mercury in both freshwater and marine food webs (Campbell et al., 2005; Al-Reasi et al., 2007; Chasar et al., 2009; Chumchal and Hambright, 2009; Swanson and Kidd, 2010); however, the majority of these studies took place in temperate or polar systems. It is very likely that trophic transfer efficiency differs between climatically distinct regions due to differences in complexity or length of food webs. "
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