Application of stable isotope mixing models for defining trophic biomagnification pathways of mercury and selenium

Abstract

Trophic models based on nitrogen stable isotope ratios (d 15 N) have been shown to predict changes in mercury (Hg) concentrations in fish; however, they are usually applied at the ecosystem scale and are rarely directed at known trophic pathways. We discuss a novel approach in which we combined gut contents analysis and stable isotope analyses (d 15 N and d 13 C) into a Bayesian isotopic mixing model to provide a quantitative estimate of Hg and selenium (Se) biomagnification in an estuarine food web. Estimates of the relationship between total mercury (THg) and methylmercury (MeHg) were significantly improved in mixing model-adjusted food webs over models that included all known prey sources. Spatial differences in dietary composition and MeHg bioavailability offer strong evidence that local food webs can have a significant effect on the biomagnification of Hg within benthic fish species. While no evidence of Se biomagnification was found, lower Se : Hg ratios at higher trophic levels could be attributed to increasing trophic Hg concentration. Furthermore, stable isotope analysis suggested Hg and Se biotransfer from benthic sources to fish. Overall, the findings highlight that isotope mixing models can be a significant aid in assessments of contaminant biomagnification, particularly when it is important to define food pathways to top predators.

Variation in Zn, C, and N isotope ratios in three stream insects

“…Variations in stable isotope ratios of 13 C/ 12 C (δ 13 C) and 15 N/ 14 N (δ 15 N) have been used extensively to examine food sources, trophic structure, and energy transfer and efficiency in lakes Rasmussen 1999, 2001;Post 2002), reservoirs (Saito et al 2001), and marine systems (Das et al 2003). In addition, interest in the sources and trophic transfer of contaminants in aquatic systems has led to studies in which δ 15 N and (or) δ 13 C values were coupled with measurements of total metal concentrations in both freshwater and marine biota (e.g., Power et al 2002;Das et al 2003;Quinn et al 2003;Larsson et al 2007;Jardine et al 2009Jardine et al , 2012Senn et al 2010;Jones et al 2014).…”

Effects of Pollution on Marine Organisms

“…A stable nitrogen isotope was used to document the biomagnification pathway of mercury and selenium occurs in fish (Jones et al 2014). Results indicated that mercury but not selenium was taken up by fish feeding upon the animals from the local area.…”