Mercury Bioaccumulation in a Stream Network

Graduate Program in Water Resources Science, Department of Ecology, Evolution and Behavior, University of Minnesota, St. Paul, Minnesota 55108, USA.
Environmental Science and Technology (Impact Factor: 5.33). 09/2009; 43(18):7016-22. DOI: 10.1021/es901525w
Source: PubMed


Mercury (Hg) contamination is common in stream and river ecosystems, but factors mediating Hg cycling in the flowing waters are much less understood than inthe lakes and wetlands. In this study, we examined the spatial patterns of methylmercury (MeHg) concentrations in the dominant groups of aquatic insect larvae across a network of streams (drainage area ranging from 0.5 to 150 km2) in northern California during summer baseflow conditions. We found that, with the exception of water striders, all invertebrate groups showed significant (p < 0.05) increases in MeHg concentrations with drainage area. The largest stream in our study watershed, the South Fork Eel River, had the highest aqueous MeHg concentration (unfiltered: 0.13-0.17 ng L(-1)) while most of the upstream tributaries had aqueous MeHg concentrations close to or below the established detection limits (0.02 ng L(-1)). A filamentous alga abundant in South Fork Eel River (Cladophora glomerata) had an exceptionally high fraction of total-Hg as MeHg (i.e., %MeHg from 50-100%). Since other potential hotspots of in-stream Hg methylation (e.g., surface sediment and deep pools) had %MeHg lower than or similar to surface water (approximately 14%), we hypothesize that Cladophora and possibly other autotrophs may serve as hotspots of in-stream MeHg production in this bedrock-dominated stream. Recent studies in other regions concluded that wetland abundance in the watershed is the predominant factor in governing Hg concentrations of stream biota. However, our results show that in the absence of wetlands, substantial spatial variation of Hg bioaccumulation can arise in stream networks due to the influence of in-stream processes.

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Available from: Martin Tsz Ki Tsui, Apr 07, 2015
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    • "[1] [90] Further, if increased DOC and Hg was the result of differences in wetlands, we would have expected to see increases in stream water MeHg as well, as significant methylation is believed to occur in wetlands . [88] [91] [92] While we anticipated DOC would be positively correlated with number of well pads within a watershed (further supporting the idea of disturbance regime), it was not. However, differences in hydrologic conditions (e.g. "
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    ABSTRACT: Mercury (Hg) is a persistent element in the environment that has the ability to bioaccumulate and biomagnify up the food chain with potentially harmful effects on ecosystems and human health. Twenty-four streams remotely located in forested watersheds in northwestern PA containing naturally reproducing Salvelinus fontinalis (brook trout), were targeted to gain a better understanding of how Marcellus shale natural gas exploration may be impacting water quality, aquatic biodiversity, and Hg bioaccumulation in aquatic ecosystems. During the summer of 2012, stream water, stream bed sediments, aquatic mosses, macroinvertebrates, crayfish, brook trout, and microbial samples were collected. All streams either had experienced hydraulic fracturing (fracked, n = 14) or not yet experienced hydraulic fracturing (non-fracked, n = 10) within their watersheds at the time of sampling. Analysis of watershed characteristics (GIS) for fracked vs non-fracked sites showed no significant differences (P > 0.05), justifying comparisons between groups. Results showed significantly higher dissolved total mercury (FTHg) in stream water (P = 0.007), lower pH (P = 0.033), and higher dissolved organic matter (P = 0.001) at fracked sites. Total mercury (THg) concentrations in crayfish (P = 0.01), macroinvertebrates (P = 0.089), and predatory macroinvertebrates (P = 0.039) were observed to be higher for fracked sites. A number of positive correlations between amount of well pads within a watershed and THg in crayfish (r = 0.76, P P P P P = 0.02), and macroinvertebrate taxa richness (r = −0.60, P = 0.01) were negatively correlated with the number of well pads within a watershed. Further investigation is needed to better elucidate relationships and pathways of observed differences in stream water chemistry, biodiversity, and Hg bioaccumulation, however, initial findings suggest Marcellus shale natural gas exploration is having an effect on aquatic ecosystems.
    Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering 04/2015; 50(5):482-500. DOI:10.1080/10934529.2015.992670 · 1.16 Impact Factor
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    • "This finding contrasts with other studies that have found a positive relationship between MeHg bioaccumulation and aqueous DOC for predatory macroinvertebrates from lakes (Rennie et al. 2005) and in macroinvertebrates from streams (shredders and predators, Riva-Murray et al. 2011; Diptera, Harding et al. 2006; filter feeders, Tsui and Finlay 2011). In another study, all FFGs had higher MeHg concentrations in streams with higher catchment areas, and DOC and nutrient concentrations also increased with catchment area (Tsui et al. 2009). In the current study, differences in OC quality and type among ecosystems may have masked effects, as this has been shown to affect the cycling of MeHg in other systems (Hall et al. 2008; Riscassi and Scanlon 2011). "
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    ABSTRACT: Macroinvertebrates are a key vector in the transfer of methylmercury (MeHg) to fish. However, the factors that affect MeHg concentrations and bioaccumulation in these organisms are not as well understood as for fish, and studies on a broad geographic scale are lacking. In this study, we gathered published and unpublished MeHg and carbon (δ(13)C) and nitrogen (δ(15)N) stable isotope data for freshwater macroinvertebrates from 119 lakes and wetlands across seven Canadian provinces, along with selected physical, chemical and biological characteristics of these systems. Overall, water pH was the most important determinant of MeHg concentrations in both predatory and non-predatory invertebrates [[Formula: see text] = 0.32, p < 0.001; multivariate canonical redundancy analysis (RDA)]. The location of lakes explained additional variation in invertebrate MeHg (partial R(2) = 0.08 and 0.06 for latitude and longitude, respectively; RDA), with higher concentrations in more easterly and southerly regions. Both invertebrate foraging behaviour and trophic position (indicated by functional feeding groups and δ(15)N values, respectively) also predicted MeHg concentrations in the organisms. Collectively, results indicate that in addition to their feeding ecology, invertebrates accumulate more MeHg in acidic systems where the supply of MeHg to the food web is typically high. MeHg concentrations in macroinvertebrates may also be influenced by larger-scale geographic differences in atmospheric mercury deposition among regions.
    Ecotoxicology 01/2014; 23(2). DOI:10.1007/s10646-013-1171-9 · 2.71 Impact Factor
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    • "Our results indicate that enhanced Hg bioaccumulation also may be associated with more depleted d 13 C (associated with greater herbivory in at least some cases) in near-neutral streams (F1 NY , S2 NY , and F3 NY ), as well as in acidic streams (M2 SC ). Explanations may include higher MeHg in periphyton than in detritus, as was found by Tsui et al. (2009), and that may result from several factors, including active uptake of aqueous MeHg by algae (Moye et al. 2002) and methylation by periphytic bacteria (Guimaraes et al. 2006; Tsui et al. 2010). A potential link between MeHg bioaccumulation and dietary carbon source characteristics (indicated by d 13 C) in low-trophic level consumers has implications for use of these organisms in mercury monitoring. "
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    ABSTRACT: We studied lower food webs in streams of two mercury-sensitive regions to determine whether variations in consumer foraging strategy and resultant dietary carbon signatures accounted for observed within-site and among-site variations in consumer mercury concentration. We collected macroinvertebrates (primary consumers and predators) and selected forage fishes from three sites in the Adirondack Mountains of New York, and three sites in the Coastal Plain of South Carolina, for analysis of mercury (Hg) and stable isotopes of carbon (δ13C) and nitrogen (δ15N). Among primary consumers, scrapers and filterers had higher MeHg and more depleted δ13C than shredders from the same site. Variation in δ13C accounted for up to 34 % of within-site variation in MeHg among primary consumers, beyond that explained by δ15N, an indicator of trophic position. Consumer δ13C accounted for 10 % of the variation in Hg among predatory macroinvertebrates and forage fishes across these six sites, after accounting for environmental aqueous methylmercury (MeHg, 5 % of variation) and base-N adjusted consumer trophic position (Δδ15N, 22 % of variation). The δ13C spatial pattern within consumer taxa groups corresponded to differences in benthic habitat shading among sites. Consumers from relatively more-shaded sites had more enriched δ13C that was more similar to typical detrital δ13C, while those from the relatively more-open sites had more depleted δ13C. Although we could not clearly attribute these differences strictly to differences in assimilation of carbon from terrestrial or in-channel sources, greater potential for benthic primary production at more open sites might play a role. We found significant variation among consumers within and among sites in carbon source; this may be related to within-site differences in diet and foraging habitat, and to among-site differences in environmental conditions that influence primary production. These observations suggest that different foraging strategies and habitats influence MeHg bioaccumulation in streams, even at relatively small spatial scales. Such influence must be considered when selecting lower trophic level consumers as sentinels of MeHg bioaccumulation for comparison within and among sites. Electronic supplementary material The online version of this article (doi:10.1007/s10646-012-1003-3) contains supplementary material, which is available to authorized users.
    Ecotoxicology 10/2012; 22(1). DOI:10.1007/s10646-012-1003-3 · 2.71 Impact Factor
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