Mercury in streams at Grand Portage National Monument (Minnesota, USA): Assessment of ecosystem sensitivity and ecological risk

Abstract

Mercury (Hg) in water, sediment, soils, seston, and biota were quantified for three streams in the Grand Portage National Monument (GRPO) in far northeastern Minnesota to assess ecosystem contamination and the potential for harmful exposure of piscivorous fish, wildlife, and humans to methylmercury (MeHg). Concentrations of total Hg in water, sediment, and soil were typical of those in forest ecosystems within the region, whereas MeHg concentrations and percent MeHg in these ecosystem components were markedly higher than values reported elsewhere in the western Great Lakes Region. Soils and sediment were Hg-enriched, containing approximately 4-fold more total Hg per unit of organic matter. We hypothesized that localized Hg enrichment was due in part to anthropogenic pollution associated with historic fur-trading activity. Bottom-up forcing of bioaccumulation was evidenced by MeHg concentrations in larval dragonflies, which were near the maxima for dragonflies sampled concurrently from five other national park units in the region. Despite its semi-remote location, GRPO is a Hg-sensitive landscape in which MeHg is produced and bioaccumulated in aquatic food webs to concentrations that pose ecological risks to MeHg-sensitive piscivores, including predatory fish, belted kingfisher, and mink.

Influence of Cladophora–Quagga Mussel Assemblages on Nearshore Methylmercury Production in Lake Michigan

“…Total Hg (HgT) levels in offshore Lake Michigan surface waters are quite low relative to those of small lakes in the upper Midwest − and more comparable to concentrations observed in the open oceans (<0.5 ng HgT L –1 ) . Methyl Hg levels have been reported as below typical quantification levels (<0.01 ng L –1 ). , A total Hg mass balance has been developed for both Lake Michigan , and Lake Superior, while a preliminary MeHg mass balance has been developed only for Lake Superior .…”

A framework for establishing restoration goals for contaminated ecosystems

“…Within the landscape context, then, it is critical that these issues be identified early in the process. Questions to address with respect to contaminants include: 1) how completely can the contaminant be removed or sequestered on the site, 2) what are the pathways by which contaminants may leave the site and how will they impact the surrounding landscape, 3) what are the sensitivities of organisms that will use or inhabit the site to any remaining contamination, and 4) are existing or potential food chains likely to amplify the contaminant in higher order predators (Rolfhus et al )? Traits of individual species and their role in the food and interaction webs of the restored site are key pieces of information: a plant that sequesters contaminants may further remediation goals, but if that plant is also a resource for organisms further up the food chain, toxicity may negate its positive remediation value and in fact may create an attractive nuisance.…”