Benthic and Pelagic Pathways of Methylmercury Bioaccumulation in Estuarine Food Webs of the Northeast United States

Abstract

Methylmercury (MeHg) is a contaminant of global concern that bioaccumulates and bioamagnifies in marine food webs. Lower trophic level fauna are important conduits of MeHg from sediment and water to estuarine and coastal fish harvested for human consumption. However, the sources and pathways of MeHg to these coastal fisheries are poorly known particularly the potential for transfer of MeHg from the sediment to biotic compartments. Across a broad gradient of human land impacts, we analyzed MeHg concentrations in food webs at ten estuarine sites in the Northeast US (from the Hackensack Meadowlands, NJ to the Gulf of Maine). MeHg concentrations in water column particulate material, but not in sediments, were predictive of MeHg concentrations in fish (killifish and Atlantic silversides). Moreover, MeHg concentrations were higher in pelagic fauna than in benthic-feeding fauna suggesting that MeHg delivery to the water column from methylation sites from within or outside of the estuary may be an important driver of MeHg bioaccumulation in estuarine pelagic food webs. In contrast, bulk sediment MeHg concentrations were only predictive of concentrations of MeHg in the infaunal worms. Our results across a broad gradient of sites demonstrate that the pathways of MeHg to lower trophic level estuarine organisms are distinctly different between benthic deposit feeders and forage fish. Thus, even in systems with contaminated sediments, transfer of MeHg into estuarine food webs maybe driven more by the efficiency of processes that determine MeHg input and bioavailability in the water column.

Mercury offloaded in Northern elephant seal hair affects coastal seawater surrounding rookery

“…In addition, accumulated organic matter in bottom sediments is a main factor affecting net MeHg production (39); therefore, inputs of marine mammal excreta and sloughed epidermis may enhance Hg methylation in nearshore sediment. Resuspension of this sediment in the nearshore environment because of wave action, coastal upwelling, storm events, and/or nearshore pinniped activity may also mobilize particulate MeHg to the water column (40), which has been established as a main driver of organic Hg bioaccumulation in estuarine pelagic food webs (41).…”

Differential bioaccumulation of potentially toxic elements in benthic and pelagic food chains in Lake Baikal

“…Samples of water, plankton, benthic invertebrates, and fish were collected at both sampling sites. Shaded areas on the map indicate major anthropogenic emission sources (based on Ciesielski et al, 2006) difference between concentrations of elements in organisms inhabiting different ecosystems, as has been reported for instance for methylmercury (MeHg) in benthic and pelagic fauna (Chen et al 2014). The relatively simple pelagic and deepwater benthic food web structures of Lake Baikal (Gurova and Pastukhov 1974;Yoshii 1999;Yoshii et al 1999) make this particular lake a good model system to study the transport of chemical elements in food chains, i.e., their bioavailability in natural waters and their bioaccumulation potential in different trophic levels (Ciesielski et al 2006).…”

Relating Fish Hg to Variations in Sediment Hg, Climate and Atmospheric Deposition

“…[71] reported that deepening the thermocline and oxycline of one lake relative to a reference lake (done by way of pumping at about 15,000 m 3 •day −1 ) increased epilimnetic temperature and oxygen saturation leading to continuing reductions in epilimnetic MeHg and Fish THg, with post-experiment effects lasting for at least one year. Hence, future changes in Fish Hg are also related to climate-induced thermocline inversions, lake-by-lake.…”

“…There is much uncertainty about how climate and atmospheric Hg deposition affect Fish THg [2] [3] [4] [5]. In part, this uncertainty is due to large and yet to be quantified land-to-lake and in-lake variations by which Hg uptake by fish increases or decreases.…”