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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    • "We examine how elevated Hg concentrations downstream of beaver dams in fluvial systems influences food web availability of Hg and the source of available carbon at the base of the food web. We hypothesized that inchannel beaver impoundments would result in an increase of downstream food web-available Hg and nutrients, and an alteration in basal resources, specifically the flow of C, leading to increased reliance on an autochthonous (algal) food source and thus greater potential for Hg to enter the food web (Tsui et al. 2009). To test our hypothesis, we quantified total Hg (THg) and MeHg concentrations in biological compartments above and below beaver dams located in oligotrophic Canadian Rocky Mountain streams, as well as nutrient concentrations, algal biomass, invertebrate density, and invertebrate dietary carbon sources. "
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    ABSTRACT: Beavers (Castor spp.) are ecosystem engineers and important modifiers of freshwater ecosystems. They create impoundments that flood the surrounding landscape and modify the flow of materials through streams, thus potentially increasing nutrients, productivity and the availability of toxic methyl mercury (MeHg) to downstream food webs. Here we quantify food web-available MeHg in water, periphyton, and invertebrates collected from 15 streams up- and down-stream from beaver impoundments in the Rocky Mountain foothills of Western Canada. While nutrients, algal biomass, and total invertebrate standing stock were not significantly elevated below ponds, MeHg concentrations (average increase of 1.73) and percent of total Hg that was MeHg (average increase of 1.33) showed a trend of higher values in all compartments downstream and the difference was significant in predatory invertebrates. This suggests that beaver impoundments can increase the availability and subsequent uptake of MeHg by basal food web organisms even if their immediate influence on nutrients and resources is limited. As beaver populations continue to rebound, more research is needed to fully characterise the effects of beavers on nutrient and contaminant cycling under different biogeochemical conditions.
    Full-text · Article · Oct 2015 · Ecosphere
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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.
    Full-text · Article · Apr 2015 · Journal of Environmental Science and Health Part A Toxic/Hazardous Substances & Environmental Engineering
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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.
    Full-text · Article · Jan 2014 · Ecotoxicology
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