Mercury methylation in the hypolimnetic waters of lakes with and without connection to wetlands in northern Wisconsin

Eckley, Chris S.; Watras, Carl J.; Hintelmann, Holger; Morrison, K. A.; Kent, Angela D.; Regnell, Olof

doi:10.1139/f04-205

Cited by 87 publications

(57 citation statements)

References 38 publications

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“…Transformations of particle-associated Hg during these transitions are little understood, especially on hour-long or shorter timescales. High methylation rates (Eckley et al, 2005) and methylmercury concentrations (Regnell et al, 1997(Regnell et al, , 2001 have been observed in anoxic hypolimnia, sometimes coinciding with high sulfate reduction rates (Watras et al, 1995). Such findings suggest that changes in Hg speciation at sulfur-bearing redox boundaries can, under some conditions, enhance the propensity for Hg to be methylated on short timescales.…”

Section: Relevant Timescales Of Mercury Reactivitymentioning

confidence: 91%

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

Slowey

Brown

2007

Geochimica et Cosmochimica Acta

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Methylmercury can accumulate in fish to concentrations unhealthy for humans and other predatory mammals. Most sources of mercury (Hg) emit inorganic species to the environment. Therefore, ecological harm occurs when inorganic Hg is converted to methylmercury. Sulfate-and iron-reducing bacteria (SRB and FeRB) methylate Hg, but the effects of processes involving oxidized and reduced forms of sulfur and iron on the reactivity of Hg, including the propensity of inorganic Hg to be methylated, are poorly understood. Under abiotic conditions, using a laboratory flow reactor, bisulfide (HS À ) was added at 40 to 250 lM h À1 to 5 g L À1 goethite (a-FeOOH) suspensions to which Hg(II) was adsorbed (30-100 nmol m À2 ) at pH 7.5. Dissolved Hg initially decreased from 10 3 or 10 4 nM (depending on initial conditions) to 10 À1 nM, during which the concentration of Hg(II) adsorbed to goethite decreased by 80% and metacinnabar (bHgS (s) ) formed, based on identification using Hg L III -edge extended X-ray absorption fine structure (EXAFS) spectroscopic analysis. The apparent coordination of oxygens surrounding Hg(II), measured with EXAFS spectroscopy, increased during one flow experiment, suggesting desorption of monodentate-bound Hg(II) while bidentate-bound Hg(II) persisted on the goethite surface. Further sulfidation increased dissolved Hg concentrations by one to two orders of magnitude (0.5 to 10 nM or 30 nM), suggesting that byproducts of bisulfide oxidation and Fe(III) reduction, primarily polysulfide and potentially Fe(II), enhanced the dissolution of b-HgS (s) and/or desorption of Hg(II). Rapid accumulation of Fe(II) in the solid phase (up to 40 lmol g À1 ) coincided with faster elevation of dissolved Hg concentrations. Fe(II) served as a proxy for elemental sulfur [S(0)], as S(0) was the dominant bisulfide oxidation product coupled to Fe(III) reduction, based on sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy. In one experiment, dissolved Hg concentrations tracked those of all sulfide species [S(-II)]. These results suggest that S(-II) reacted with S(0) to form polysulfide, which then caused the dissolution of b-HgS (s) . A secondary Fe-bearing phase resembling poorly formed green rust was observed in sulfidized solids with scanning electron microscopy, although there was no clear evidence that either surface-bound or mineralized Fe(II) strongly affected Hg speciation. Examination of interrelated processes involving S(-II) and Fe(III) revealed new modes of Hg solubilization previously not considered in Hg reactivity models.

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Section: Relevant Timescales Of Mercury Reactivitymentioning

confidence: 91%

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

Slowey

Brown

2007

Geochimica et Cosmochimica Acta

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“…The balance between methylation and demethylation apparently resets again each spring as a period of renewed meHg accumulation begins below the oxic/anoxic boundary. Spring methylation activity may start in sediments and migrate into the water column as anaerobic microbes move upward toward the source of limiting nutrients, like sulfate and DOC Eckley et al 2005).…”

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confidence: 99%

The methylmercury cycle in Little Rock Lake during experimental acidification and recovery

et al. 2006

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The cycle of waterborne methylmercury (meHg) in Little Rock Lake is characterized by a period of accumulation during summertime (when the lake is warm and open to the atmosphere) and a period of decline during winter (when the lake is sealed by ice). We followed this cycle for 16 yr, during which time the lake was acidified with H 2 SO 4 and then allowed to recover naturally as part of a long-term field experiment on acidic rain. Mass balance was used to quantify meHg sources and sinks during acidification and recovery. Although year-to-year variability in the summertime accumulation of meHg was high during both acidified and de-acidified years (C.V. ϭ 0.7 and 0.5, respectively), on average 65% more meHg accumulated in the water column during acidification. Most of the meHg mass accumulated in the anoxic hypolimnion (Ͼ70%), even though the hypolimnion constituted Ͻ5% of the lake volume. In hypolimnetic waters, we observed a direct correlation between the maximum meHg concentration and the sulfate deficit for each year (r 2 ϭ 0.5-0.9) and a direct correlation between meHg and sulfide concentrations (r 2 ϭ 0.7). Sulfide was directly related to dissolved organic carbon at concentrations between 300 and 600 mol L Ϫ1 carbon (C). Seasonal changes in waterborne Hg (II) , meHg, and sulfate reduction covaried with the atmospheric deposition of Hg (II) and SO . Across all years, the interaction term [SO ϫ Hg (II) ] explained 70% of the variationin the meHg accumulation rate during summer. These results indicate that meHg production was co-mediated by several simultaneously occurring processes that affect the supply of Hg (II) substrate to the anoxic hypolimnion and the activity of methylating bacteria that are present there. They imply that meHg levels in lakes may respond to future changes in atmospheric Hg deposition in a rapid but complex way, modulated by environmental variables that can interact synergistically with Hg (II) supply. Such variables include sulfate in acid rain, organic carbon in terrestrial runoff, and temperature.Acid rain and methylmercury (meHg) contamination emerged as limnological issues during the 1970s, but it was not until the late 1980s that both were linked to atmospheric deposition and widespread human perturbation of the sulfur and mercury cycles. A direct connection between acid deposition and the aquatic meHg cycle was first indicated by early synoptic surveys that documented strong negative correlations between lake water pH and the concentration of meHg in fish (Spry and Wiener 1991; Wiener and Spry 1996). Today, pH remains the strongest environmental cor-1 Corresponding author (cjwatras@wisc.edu). AcknowledgmentsWe thank Nick Bloom, Emily Greenberg, Steve Claas, Beth Kuhn, Rick Back, Vanessa Visman, Jeff Rubsam, Lana Fanberg, Bruce Rodger, and many others for assistance throughout this longterm project. Mercury analyses prior to 1993 were conducted at Frontier Geosciences, Seattle, Washington.

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“…Suggested values for both methylation and demethylation rates are 10 −5 -10 −2 d −1 [41]. Methylation rate ranged between 0.01 to 0.09 d −1 in a clear lake in Wisconsin [51]. Studies by Carroll et al [52] and Oremland et al [53] Tables 6 and 7.…”

Section: Resultsmentioning

confidence: 99%

Enhanced Two Dimensional Hydrodynamic and Water Quality Model (CE-QUAL-W2) for Simulating Mercury Transport and Cycling in Water Bodies

Zhu

Zhang

Liu

2017

Water

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CE-QUAL-W2 (W2) is a widely-used two-dimensional, laterally averaged, longitudinal/ vertical, hydrodynamic and water quality model. This model was modified and enhanced to include a mercury (Hg) simulation module for simulating Hg transport and cycling in water bodies. The Hg simulation module in W2 is able to model the physical and biochemical processes including adsorption and desorption of Hg species on multi-solids, settling and resuspension, sediment burial of adsorbed Hg, diffusive exchange between water column and sediment layer, volatilization, and biogeochemical transformations among Hg species. This paper describes the Hg simulation module, W2 model validation and its application to the Xiaxi River, China, a historical Hg contaminated water body. The W2 model was evaluated using the Xiaxi River data collected in 2007 and 2008. Model results show that W2 was able to predict the total Hg and methylmercury concentrations observed for the Xiaxi River. The Xiaxi River W2 model also provides a foundation for the future investigations of Hg contamination in the Xiaxi River. This application demonstrated the W2 model capability in predicting complex transport and cycling of Hg species in water bodies.

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Mercury methylation in the hypolimnetic waters of lakes with and without connection to wetlands in northern Wisconsin

Cited by 87 publications

References 38 publications

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

Transformations of mercury, iron, and sulfur during the reductive dissolution of iron oxyhydroxide by sulfide

The methylmercury cycle in Little Rock Lake during experimental acidification and recovery

Enhanced Two Dimensional Hydrodynamic and Water Quality Model (CE-QUAL-W2) for Simulating Mercury Transport and Cycling in Water Bodies

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