Assessment of mercury bioaccumulation within the pelagic food web of lakes in the western Great Lakes region

Abstract

While mercury is a health hazard to humans and wildlife, the biogeochemical processes responsible for its bioaccumulation in pelagic food webs are still being examined. Previous studies have indicated both "bottom-up" control of piscivorous fish Hg content through methylmercury.(MeHg) supply, as well as site-specific trophic factors. We evaluated ten studies from the western Great Lakes region to examine the similarity of MeHg trophic transfer efficiency within the pelagic food web, and assessed regional-scale spatial variability. Analyses of bioaccumulation and biomagnification factors between water, seston, zooplankton, and preyfish indicated that the largest increases in MeHg occurred at the base of the food web, and that the relative extent of trophic transfer was similar between sites. Positive correlations were observed between aqueous unfiltered MeHg, total Hg, and dissolved organic carbon, and measures of the efficiency of MeHg trophic transfer were consistent across widely disparate systems (both natural and experimentally manipulated) throughout North America. Such similarity suggests that the aqueous supply of MeHg is largely controlling bioaccumulation in pelagic food webs, while local, lake-specific variability can result from an array of trophic (biological) factors.

A Comparison of Mercury Biomagnification through Lacustrine Food Webs Supporting Brook Trout (Salvelinus fontinalis) and Other Salmonid Fishes

“…Tahoe Lake also had among the highest concentrations of MeHg in invertebrates, second only to A Lake, and was more acidic, had higher TOC, and had lower Ca 2+ concentrations than all systems but A Lake. While less is known about how these factors affect TMS, they are conducive to increased MeHg production and input to the base of food webs, as discussed above and in French et al (2014) and Rolfhus et al (2011), and lower Hg biomagnification in fish has been observed when their prey Hg concentrations are higher .…”

“…Interestingly, TMS values are either higher (this study, Kidd et al, 2012;Verburg et al, 2014) or lower (Clayden et al, 2013;Lavoie et al, 2013) in lakes with greater TP for reasons that are unknown and warrant further investigation. While there are numerous studies in the literature that have quantified the trophic transfer of Hg using δ 15 N (e.g., Rolfhus et al, 2011), most have not examined whether the TMS values are related to system characteristics. In summary, results from this study on Brook Trout in New Brunswick lakes support the paradigms that trophic position, source of dietary carbon, and size affect concentrations of this toxic element in fish and that higher Hg is found in biota from acidic systems, and provide new knowledge on the magnitude of Hg biomagnification through lacustrine food webs supporting Brook Trout.…”

Mercury in the Great Lakes region: bioaccumulation, spatiotemporal patterns, ecological risks, and policy

“…Several studies have determined that approximately two-thirds of the mercury released to today's global environment originates from human activities (Mason et al 2005;UNEP Chemicals Branch 2008). Toxicological concerns about mercury contamination focus primarily on methylmercury, a highly toxic compound that readily accumulates in organisms and biomagnifies in food webs to concentrations that vastly exceed those in surface water (Wiener et al 2003;Driscoll et al 2007;Scheuhammer et al 2007;Chasar et al 2009;Rolfhus et al 2011). Although most of the mercury in air, atmospheric deposition, water, soil, and sediment exists as inorganic forms, nearly all of the mercury accumulated by fish and higher trophic level organisms is methylmercury (Wiener et al 2003;Chasar et al 2009).…”

“…The three food-web studies in this issue showed that the concentration of methylmercury at the base of an aquatic food web, as well as trophic position and food chain length, exert important controls on methylmercury exposure in biota of upper trophic levels. Rolfhus et al (2011) examined the bioaccumulation of methylmercury in the lower pelagic food webs of lakes in the western Great Lakes region. The concentration of methylmercury in unfiltered water was positively correlated with dissolved organic carbon (DOC).…”

“…Rates of trophic transfer in natural and experimental systems were similar among sites. The similarities in transfer efficiencies between trophic levels led Rolfhus et al (2011) to conclude that the supply of methylmercury and its concentration at the base of the food web are key factors controlling bioaccumulation in pelagic, lacustrine food webs.…”