19 research outputs found

    Mercury Cycling in Stream Ecosystems. 1. Water Column Chemistry and Transport

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    We studied total mercury (THg) and methylmercury (MeHg) in eight streams, located in Oregon, Wisconsin, and Florida, that span large ranges in climate, landscape characteristics, atmospheric Hg deposition, and water chemistry. While atmospheric deposition was the source of Hg at each site, basin characteristics appeared to mediate this source by providing controls on methylation and fluvial THg and MeHg transport. Instantaneous concentrations of filtered total mercury (FTHg) and filtered methylmercury (FMeHg) exhibited strong positive correlations with both dissolved organic carbon (DOC) concentrations and streamflow for most streams, whereas mean FTHg and FMeHg concentrations were correlated with wetland density of the basins. For all streams combined, whole water concentrations (sum of filtered and particulate forms) of THg and MeHg correlated strongly with DOC and suspended sediment concentrations in the water column

    Lacustrine Responses to Decreasing Wet Mercury Deposition RatesResults from a Case Study in Northern Minnesota

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    We present a case study comparing metrics of methylmercury (MeHg) contamination for four undeveloped lakes in Voyageurs National Park to wet atmospheric deposition of mercury (Hg), sulfate (SO<sub>4</sub><sup>–2</sup>), and hydrogen ion (H<sup>+</sup>) in northern Minnesota. Annual wet Hg, SO<sub>4</sub><sup>–2</sup>, and H<sup>+</sup> deposition rates at two nearby precipitation monitoring sites indicate considerable decreases from 1998 to 2012 (mean decreases of 32, 48, and 66%, respectively). Consistent with decreases in the atmospheric pollutants, epilimnetic aqueous methylmercury (MeHg<sub>aq</sub>) and mercury in small yellow perch (Hg<sub>fish</sub>) decreased in two of four lakes (mean decreases of 46.5% and 34.5%, respectively, between 2001 and 2012). Counter to decreases in the atmospheric pollutants, MeHg<sub>aq</sub> increased by 85% in a third lake, whereas Hg<sub>fish</sub> increased by 80%. The fourth lake had two disturbances in its watershed during the study period (forest fire; changes in shoreline inundation due to beaver activity); this lake lacked overall trends in MeHg<sub>aq</sub> and Hg<sub>fish</sub>. The diverging responses among the study lakes exemplify the complexity of ecosystem responses to decreased loads of atmospheric pollutants

    Mercury Cycling in Stream Ecosystems. 2. Benthic Methylmercury Production and Bed Sediment−Pore Water Partitioning

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    Mercury speciation, controls on methylmercury (MeHg) production, and bed sediment−pore water partitioning of total Hg (THg) and MeHg were examined in bed sediment from eight geochemically diverse streams where atmospheric deposition was the predominant Hg input. Across all streams, sediment THg concentrations were best described as a combined function of sediment percent fines (%fines; particles < 63 μm) and organic content. MeHg concentrations were best described as a combined function of organic content and the activity of the Hg(II)-methylating microbial community and were comparable to MeHg concentrations in streams with Hg inputs from industrial and mining sources. Whole sediment tin-reducible inorganic reactive Hg (Hg(II)<sub>R</sub>) was used as a proxy measure for the Hg(II) pool available for microbial methylation. In conjunction with radiotracer-derived rate constants of <sup>203</sup>Hg(II) methylation, Hg(II)<sub>R</sub> was used to calculate MeHg production potential rates and to explain the spatial variability in MeHg concentration. The %Hg(II)<sub>R</sub> (of THg) was low (2.1 ± 5.7%) and was inversely related to both microbial sulfate reduction rates and sediment total reduced sulfur concentration. While sediment THg concentrations were higher in urban streams, %MeHg and %Hg(II)<sub>R</sub> were higher in nonurban streams. Sediment pore water distribution coefficients (log <i>K</i><sub>d</sub>’s) for both THg and MeHg were inversely related to the log-transformed ratio of pore water dissolved organic carbon (DOC) to bed sediment %fines. The stream with the highest drainage basin wetland density also had the highest pore water DOC concentration and the lowest log <i>K</i><sub>d</sub>’s for both THg and MeHg. No significant relationship existed between overlying water MeHg concentrations and those in bed sediment or pore water, suggesting upstream sources of MeHg production may be more important than local streambed production as a driver of water column MeHg concentration in drainage basins that receive Hg inputs primarily from atmospheric sources

    Spatial and Seasonal Variability of Dissolved Methylmercury in Two Stream Basins in the Eastern United States

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    We assessed methylmercury (MeHg) concentrations across multiple ecological scales in the Edisto (South Carolina) and Upper Hudson (New York) River basins. Out-of-channel wetland/floodplain environments were primary sources of filtered MeHg (F-MeHg) to the stream habitat in both systems. Shallow, open-water areas in both basins exhibited low F-MeHg concentrations and decreasing F-MeHg mass flux. Downstream increases in out-of-channel wetlands/floodplains and the absence of impoundments result in high MeHg throughout the Edisto. Despite substantial wetlands coverage and elevated F-MeHg concentrations at the headwater margins, numerous impoundments on primary stream channels favor spatial variability and lower F-MeHg concentrations in the Upper Hudson. The results indicated that, even in geographically, climatically, and ecologically diverse streams, production in wetland/floodplain areas, hydrologic transport to the stream aquatic environment, and conservative/nonconservative attenuation processes in open water areas are fundamental controls on dissolved MeHg concentrations and, by extension, MeHg availability for potential biotic uptake

    Optimizing Stream Water Mercury Sampling for Calculation of Fish Bioaccumulation Factors

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    Mercury (Hg) bioaccumulation factors (BAFs) for game fishes are widely employed for monitoring, assessment, and regulatory purposes. Mercury BAFs are calculated as the fish Hg concentration (Hg<sub>fish</sub>) divided by the water Hg concentration (Hg<sub>water</sub>) and, consequently, are sensitive to sampling and analysis artifacts for fish and water. We evaluated the influence of water sample timing, filtration, and mercury species on the modeled relation between game fish and water mercury concentrations across 11 streams and rivers in five states in order to identify optimum Hg<sub>water</sub> sampling approaches. Each model included fish trophic position, to account for a wide range of species collected among sites, and flow-weighted Hg<sub>water</sub> estimates. Models were evaluated for parsimony, using Akaike’s Information Criterion. Better models included filtered water methylmercury (FMeHg) or unfiltered water methylmercury (UMeHg), whereas filtered total mercury did not meet parsimony requirements. Models including mean annual FMeHg were superior to those with mean FMeHg calculated over shorter time periods throughout the year. FMeHg models including metrics of high concentrations (80th percentile and above) observed during the year performed better, in general. These higher concentrations occurred most often during the growing season at all sites. Streamflow was significantly related to the probability of achieving higher concentrations during the growing season at six sites, but the direction of influence varied among sites. These findings indicate that streamwater Hg collection can be optimized by evaluating site-specific FMeHg – UMeHg relations, intra-annual temporal variation in their concentrations, and streamflow-Hg dynamics

    Shallow Groundwater Mercury Supply in a Coastal Plain Stream

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    Fluvial methylmercury (MeHg) is attributed to methylation in up-gradient wetland areas. This hypothesis depends on efficient wetland-to-stream hydraulic transport under nonflood and flood conditions. Fluxes of water and dissolved (filtered) mercury (Hg) species (FMeHg and total Hg (FTHg)) were quantified in April and July of 2009 in a reach at McTier Creek, South Carolina to determine the relative importance of tributary surface water and shallow groundwater Hg transport from wetland/floodplain areas to the stream under nonflood conditions. The reach represented less than 6% of upstream main-channel distance and 2% of upstream basin area. Surface-water discharge increased within the reach by approximately 10%. Mean FMeHg and FTHg fluxes increased within the reach by 23–27% and 9–15%, respectively. Mass balances indicated that, under nonflood conditions, the primary supply of water, FMeHg, and FTHg within the reach (excluding upstream surface water influx) was groundwater discharge, rather than tributary transport from wetlands, in-stream MeHg production, or atmospheric Hg deposition. These results illustrate the importance of riparian wetland/floodplain areas as sources of fluvial MeHg and of groundwater Hg transport as a fundamental control on Hg supply to Coastal Plain streams

    Heatmap of two-way cluster analysis performed on rank-transformed sediment data (only includes chemicals detected ≥30% of sediment samples).

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    <p>Data ranks are represented by color; lighter colors correspond to lower ranks. E2, 17β-estradiol; OP, 4-<i>tert</i>-octylphenol; ANQN, anthraquinone; BSS, β-sitosterol; BSM, β-stigmastanol; CHOL, cholesterol; IND, indole; MIND, 3-methyl-indole; MP, <i>p</i>-cresol; ISO, isophorone; DPHD; diphenhydramine; DCBZ, 1,4-dichlorobenzene; AHTN, acetyl hexamethyl tetrahydronaphthalene; HHCB, hexahydrohexamethyl cyclopentabenzopyran; A4, 4-androsterne-3,17-dione; AND, <i>cis</i>-androsterone; DMNAP, 2,6-dimethylnaphthalane; E1, estrone; BPA, bisphenol A; NAP, naphthalene; 1-MNAP, 1-methylnaphthalene; 2-MNAP, 2-methylnaphthalene; CARB, carbazole; ANT, anthracene; BaP, benzo(a)pyrene; PHEN, phenanthrene; FLU, fluoranthene; PYR, pyrene.</p

    Contaminants of emerging concern in tributaries to the Laurentian Great Lakes: I. Patterns of occurrence

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    <div><p>Human activities introduce a variety of chemicals to the Laurentian Great Lakes including pesticides, pharmaceuticals, flame retardants, plasticizers, and solvents (collectively referred to as contaminants of emerging concern or CECs) potentially threatening the vitality of these valuable ecosystems. We conducted a basin-wide study to identify the presence of CECs and other chemicals of interest in 12 U.S. tributaries to the Laurentian Great Lakes during 2013 and 2014. A total of 292 surface-water and 80 sediment samples were collected and analyzed for approximately 200 chemicals. A total of 32 and 28 chemicals were detected in at least 30% of water and sediment samples, respectively. Concentrations ranged from 0.0284 (indole) to 72.2 (cholesterol) μg/L in water and 1.75 (diphenhydramine) to 20,800 μg/kg (fluoranthene) in sediment. Cluster analyses revealed chemicals that frequently co-occurred such as pharmaceuticals and flame retardants at sites receiving similar inputs such as wastewater treatment plant effluent. Comparison of environmental concentrations to water and sediment-quality benchmarks revealed that polycyclic aromatic hydrocarbon concentrations often exceeded benchmarks in both water and sediment. Additionally, bis(2-ethylhexyl) phthalate and dichlorvos concentrations exceeded water-quality benchmarks in several rivers. Results from this study can be used to understand organism exposure, prioritize river basins for future management efforts, and guide detailed assessments of factors influencing transport and fate of CECs in the Great Lakes Basin.</p></div

    Great Lakes Basin map showing U.S. tributaries sampled in 2013–14.

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    <p>Numbers indicate the river basin sampled within the designated watershed. Colors depict land use as described in Homer et al. [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182868#pone.0182868.ref026" target="_blank">26</a>]. Generally, red/pink represent developed, yellow/brown represent agriculture, greens are forest, and blues are wetlands and open water.</p

    Heatmap of two-way cluster analysis performed on rank-transformations of maximum concentrations detected per site (only includes chemicals detected ≥30% of water samples).

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    <p>Data ranks are represented by color; lighter colors correspond to lower ranks. NIC, nicotine; ISO, isophorone; ATZ, atrazine; METCH, metolachlor; IND, indole; BSS, β-sitosterol; CHOL, cholesterol; CAFF, caffeine; DEET, N,N-Diethyl-<i>meta</i>-toluamide; COP, 3β-coprostanol; ANQN, 9,10-anthraquinone; FLU, fluoranthene; PYR, pyrene; ATEN, atenolol; COT, cotinine; FYROL FR2, tris (dichloroisopropyl) phosphate; TBEP, tris(2-butoxyethyl) phosphate; ACYC, acyclovir; METF, metformin; LID, lidocaine; HHCB, hexahydrohexamethyl cyclopentabenzopyran; METP, metoprolol; METHO, methocarbamol; MPB, meprobamate; SMX, sulfamethoxazole; MBTZ, methyl-1<i>H</i>-benzotriazole; TRIAM, triamterene; FEXO, fexofendadine; CMZ, carbamazepine; TRAM, tramadol; DESVEN, desvenlafaxine; VEN, venlafaxine.</p
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