Stable carbon and nitrogen isotopes explain methylmercury concentrations in stream food webs of Lake George, New York (USA)

• Published in: Ecotoxicology (London) 2022-07, Vol.31 (5), p.808-821
• Main Authors: Swinton, M. W., Myer, P. K., Schaller, M. F., Pettitt, E. A., Farrell, J. L., Nierzwicki-Bauer, S. A.
• Format: Article
• Language: English
• Subjects: Algae; Allochthonous deposits; Analysis; Bioaccumulation; Bioavailability; Biofilms; Biological magnification; Carbon; Carbon dioxide; Components; Dimethylmercury; Earth and Environmental Science; Ecology; Ecosystem components; Ecotoxicology; Environment; Environmental factors; Environmental Management; Epilithic algae; Fish; Food chains; Food chains (Ecology); Food contamination; Food webs; Health aspects; Health risks; Isotopes; Lakes; Leaf litter; Leaves; Macroinvertebrates; Mathematical analysis; Mercury; Mercury (metal); Methyl mercury; Methylmercury; Nitrogen; Nitrogen isotopes; Predators; Primary production; Rivers; Stream order; Streams; Variability; Water chemistry; Watersheds; Zoobenthos
• ISSN: 0963-9292; 1573-3017
• DOI: 10.1007/s10646-022-02548-0

Mercury has been studied extensively in lakes due to health risks associated with the consumption of contaminated fish, while stream ecosystems have received less attention. To better understand mercury bioavailability in the lower food web of streams, we collected macroinvertebrates (predators and detritivore) along with autochthonous (epilithic algae) and allochthonous (leaf litter) basal resources in eight streams entering Lake George. Samples were analyzed for methylmercury (MeHg), total mercury, and carbon and nitrogen isotopes (δ 13 C & δ 15 N) to determine how mercury concentrations in basal resources, biomagnification rates, and environmental factors (watershed characteristics and water chemistry) effected MeHg concentrations in predatory macroinvertebrates. While biomagnification rates, calculated as trophic magnification slope, explained between 68% and 98% of MeHg variability within a stream food web, the range was small (0.310–0.387) resulting in the biotic components following a consistent pattern of increasing MeHg among streams. The stream order was negatively related to basin slope for all biotic components and explained 70% of MeHg variability in predatory macroinvertebrates. Methylmercury concentrations were significantly and negatively related to δ 13 C in predators, epilithic algae, and leaf litter. We believe the biofilms on leaf litter utilized bacterial-respired carbon dioxide decreasing δ 13 C (