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Influence of dietary carbon on mercury bioaccumulation in streams of the Adirondack Mountains of New York and the Coastal Plain of South Carolina, USA.

Riva-Murray K, Bradley PM, Chasar LC, Button DT, Brigham ME, Scudder Eikenberry BC, Journey CA, Lutz MA - Ecotoxicology (2012)

Bottom Line: Consumers from relatively more-shaded sites had more enriched δ(13)C that was more similar to typical detrital δ(13)C, while those from the relatively more-open sites had more depleted δ(13)C.These observations suggest that different foraging strategies and habitats influence MeHg bioaccumulation in streams, even at relatively small spatial scales.Such influence must be considered when selecting lower trophic level consumers as sentinels of MeHg bioaccumulation for comparison within and among sites.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180, USA. krmurray@usgs.gov

ABSTRACT
We studied lower food webs in streams of two mercury-sensitive regions to determine whether variations in consumer foraging strategy and resultant dietary carbon signatures accounted for observed within-site and among-site variations in consumer mercury concentration. We collected macroinvertebrates (primary consumers and predators) and selected forage fishes from three sites in the Adirondack Mountains of New York, and three sites in the Coastal Plain of South Carolina, for analysis of mercury (Hg) and stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N). Among primary consumers, scrapers and filterers had higher MeHg and more depleted δ(13)C than shredders from the same site. Variation in δ(13)C accounted for up to 34 % of within-site variation in MeHg among primary consumers, beyond that explained by δ(15)N, an indicator of trophic position. Consumer δ(13)C accounted for 10 % of the variation in Hg among predatory macroinvertebrates and forage fishes across these six sites, after accounting for environmental aqueous methylmercury (MeHg, 5 % of variation) and base-N adjusted consumer trophic position (Δδ(15)N, 22 % of variation). The δ(13)C spatial pattern within consumer taxa groups corresponded to differences in benthic habitat shading among sites. Consumers from relatively more-shaded sites had more enriched δ(13)C that was more similar to typical detrital δ(13)C, while those from the relatively more-open sites had more depleted δ(13)C. Although we could not clearly attribute these differences strictly to differences in assimilation of carbon from terrestrial or in-channel sources, greater potential for benthic primary production at more open sites might play a role. We found significant variation among consumers within and among sites in carbon source; this may be related to within-site differences in diet and foraging habitat, and to among-site differences in environmental conditions that influence primary production. These observations suggest that different foraging strategies and habitats influence MeHg bioaccumulation in streams, even at relatively small spatial scales. Such influence must be considered when selecting lower trophic level consumers as sentinels of MeHg bioaccumulation for comparison within and among sites.

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a Methylmercury concentration, b carbon isotope ratio (δ13C), and c nitrogen isotope ratio (δ15N) in primary consumers collected from three NY sites and one SC site during spring, summer, and fall. Macroinvertebrate samples are composites collected from throughout each reach. Taxa names of invertebrate larvae are as follows: HE, flat-head mayflies (Heptageniidae); HY, net-spinner caddisflies (Hydropsychidae); LS, stick-builder northern case-maker caddisflies (Limnephilidae); LH, hut-builder northern case-maker caddisflies (Limnephilidae); TI, craneflies (Tipulidae: Tipula spp.). Taxa with same letter above symbols within sites are not significantly different (p > 0.05). F statistic (subscripts are degrees of freedom) and p-values are based on analyses using all taxa within each site
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Fig2: a Methylmercury concentration, b carbon isotope ratio (δ13C), and c nitrogen isotope ratio (δ15N) in primary consumers collected from three NY sites and one SC site during spring, summer, and fall. Macroinvertebrate samples are composites collected from throughout each reach. Taxa names of invertebrate larvae are as follows: HE, flat-head mayflies (Heptageniidae); HY, net-spinner caddisflies (Hydropsychidae); LS, stick-builder northern case-maker caddisflies (Limnephilidae); LH, hut-builder northern case-maker caddisflies (Limnephilidae); TI, craneflies (Tipulidae: Tipula spp.). Taxa with same letter above symbols within sites are not significantly different (p > 0.05). F statistic (subscripts are degrees of freedom) and p-values are based on analyses using all taxa within each site

Mentions: The number of primary consumer composite samples collected per feeding group ranged from two to 20 among all three Fishing Brook sites and M2SC; few samples of any primary consumers were collected from G1SC and M1SC. Detailed sample data can be found in Beaulieu et al. (2012). Primary consumers differed with respect to MeHg concentrations, δ13C, and δ15N within each of the four sites from which multiple primary consumers were collected (Fig. 2), but patterns were generally consistent among sites. At all four sites, shredders had the lowest concentrations, and filterers, or filterers and scrapers, had the highest concentrations. Differences also were apparent within the shredder feeding group at two of the three NY sites, where MeHg concentrations were higher in hut-builder caddisflies than in stick-builder caddisflies. Within-site δ13C patterns among primary consumers were generally the inverse of the MeHg pattern. Shredders had the most enriched δ13C (which was the most similar to typical detrital δ13C), and filterers, or filterers and scrapers, had the most depleted δ13C (which was the most distinct from typical detrital δ13C). Scraper δ13C was depleted relative to one of the shredders (i.e., stick-builder caddisflies) at all three NY sites, and also was depleted relative to hut-builder caddisflies at F1NY.Fig. 2


Influence of dietary carbon on mercury bioaccumulation in streams of the Adirondack Mountains of New York and the Coastal Plain of South Carolina, USA.

Riva-Murray K, Bradley PM, Chasar LC, Button DT, Brigham ME, Scudder Eikenberry BC, Journey CA, Lutz MA - Ecotoxicology (2012)

a Methylmercury concentration, b carbon isotope ratio (δ13C), and c nitrogen isotope ratio (δ15N) in primary consumers collected from three NY sites and one SC site during spring, summer, and fall. Macroinvertebrate samples are composites collected from throughout each reach. Taxa names of invertebrate larvae are as follows: HE, flat-head mayflies (Heptageniidae); HY, net-spinner caddisflies (Hydropsychidae); LS, stick-builder northern case-maker caddisflies (Limnephilidae); LH, hut-builder northern case-maker caddisflies (Limnephilidae); TI, craneflies (Tipulidae: Tipula spp.). Taxa with same letter above symbols within sites are not significantly different (p > 0.05). F statistic (subscripts are degrees of freedom) and p-values are based on analyses using all taxa within each site
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3526734&req=5

Fig2: a Methylmercury concentration, b carbon isotope ratio (δ13C), and c nitrogen isotope ratio (δ15N) in primary consumers collected from three NY sites and one SC site during spring, summer, and fall. Macroinvertebrate samples are composites collected from throughout each reach. Taxa names of invertebrate larvae are as follows: HE, flat-head mayflies (Heptageniidae); HY, net-spinner caddisflies (Hydropsychidae); LS, stick-builder northern case-maker caddisflies (Limnephilidae); LH, hut-builder northern case-maker caddisflies (Limnephilidae); TI, craneflies (Tipulidae: Tipula spp.). Taxa with same letter above symbols within sites are not significantly different (p > 0.05). F statistic (subscripts are degrees of freedom) and p-values are based on analyses using all taxa within each site
Mentions: The number of primary consumer composite samples collected per feeding group ranged from two to 20 among all three Fishing Brook sites and M2SC; few samples of any primary consumers were collected from G1SC and M1SC. Detailed sample data can be found in Beaulieu et al. (2012). Primary consumers differed with respect to MeHg concentrations, δ13C, and δ15N within each of the four sites from which multiple primary consumers were collected (Fig. 2), but patterns were generally consistent among sites. At all four sites, shredders had the lowest concentrations, and filterers, or filterers and scrapers, had the highest concentrations. Differences also were apparent within the shredder feeding group at two of the three NY sites, where MeHg concentrations were higher in hut-builder caddisflies than in stick-builder caddisflies. Within-site δ13C patterns among primary consumers were generally the inverse of the MeHg pattern. Shredders had the most enriched δ13C (which was the most similar to typical detrital δ13C), and filterers, or filterers and scrapers, had the most depleted δ13C (which was the most distinct from typical detrital δ13C). Scraper δ13C was depleted relative to one of the shredders (i.e., stick-builder caddisflies) at all three NY sites, and also was depleted relative to hut-builder caddisflies at F1NY.Fig. 2

Bottom Line: Consumers from relatively more-shaded sites had more enriched δ(13)C that was more similar to typical detrital δ(13)C, while those from the relatively more-open sites had more depleted δ(13)C.These observations suggest that different foraging strategies and habitats influence MeHg bioaccumulation in streams, even at relatively small spatial scales.Such influence must be considered when selecting lower trophic level consumers as sentinels of MeHg bioaccumulation for comparison within and among sites.

View Article: PubMed Central - PubMed

Affiliation: U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180, USA. krmurray@usgs.gov

ABSTRACT
We studied lower food webs in streams of two mercury-sensitive regions to determine whether variations in consumer foraging strategy and resultant dietary carbon signatures accounted for observed within-site and among-site variations in consumer mercury concentration. We collected macroinvertebrates (primary consumers and predators) and selected forage fishes from three sites in the Adirondack Mountains of New York, and three sites in the Coastal Plain of South Carolina, for analysis of mercury (Hg) and stable isotopes of carbon (δ(13)C) and nitrogen (δ(15)N). Among primary consumers, scrapers and filterers had higher MeHg and more depleted δ(13)C than shredders from the same site. Variation in δ(13)C accounted for up to 34 % of within-site variation in MeHg among primary consumers, beyond that explained by δ(15)N, an indicator of trophic position. Consumer δ(13)C accounted for 10 % of the variation in Hg among predatory macroinvertebrates and forage fishes across these six sites, after accounting for environmental aqueous methylmercury (MeHg, 5 % of variation) and base-N adjusted consumer trophic position (Δδ(15)N, 22 % of variation). The δ(13)C spatial pattern within consumer taxa groups corresponded to differences in benthic habitat shading among sites. Consumers from relatively more-shaded sites had more enriched δ(13)C that was more similar to typical detrital δ(13)C, while those from the relatively more-open sites had more depleted δ(13)C. Although we could not clearly attribute these differences strictly to differences in assimilation of carbon from terrestrial or in-channel sources, greater potential for benthic primary production at more open sites might play a role. We found significant variation among consumers within and among sites in carbon source; this may be related to within-site differences in diet and foraging habitat, and to among-site differences in environmental conditions that influence primary production. These observations suggest that different foraging strategies and habitats influence MeHg bioaccumulation in streams, even at relatively small spatial scales. Such influence must be considered when selecting lower trophic level consumers as sentinels of MeHg bioaccumulation for comparison within and among sites.

Show MeSH
Related in: MedlinePlus