Methylmercury Declines in a Boreal Peatland When Experimental Sulfate Deposition Decreases

Wasik, Jill K. Coleman; Mitchell, Carl P. J.; Engstrom, Daniel R.; Swain, Edward B.; Monson, Bruce A.; Balogh, Steven J.; Jeremiason, Jeff D.; Branfireun, Brian A.; Eggert, Susan L.; Kolka, Randall K.; Almendinger, James E.

doi:10.1021/es300865f

Cited by 50 publications

(60 citation statements)

References 56 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Following rewetting events in the spring and fall of 2007, sulfate concentrations in experimental‐treatment pore waters were more than twice that in the control treatment, while sulfate concentrations in the recovery treatment were intermediate between the control and experimental treatments (Figures and ). Because sulfate disappeared from pore waters following sulfate additions and rewetting events, and because no significant differences were found in the solid total‐sulfur pool among the treatments [ Coleman Wasik et al , ], it appears that a greater fraction of the organic sulfur pool was available for release in peat that had recently experienced elevated sulfate loading. Furthermore, the finding that sulfate release was greater in the recovery treatment than in the control treatment 2 years after sulfate additions had ended indicates that this more labile organic sulfur pool persisted for some time after elevated sulfate deposition had ceased.…”

Section: Discussionmentioning

confidence: 99%

The effects of hydrologic fluctuation and sulfate regeneration on mercury cycling in an experimental peatland

et al. 2015

View full text Add to dashboard Cite

A series of severe droughts during the course of a long-term, atmospheric sulfate-deposition experiment in a boreal peatland in northern Minnesota created a unique opportunity to study how methylmercury (MeHg) production responds to drying and rewetting events in peatlands under variable levels of sulfate loading. Peat oxidation during extended dry periods mobilized sulfate, MeHg, and total mercury (Hg T ) to peatland pore waters during rewetting events. Pore water sulfate concentrations were inversely related to antecedent moisture conditions and proportional to past and current levels of atmospheric sulfate deposition. Severe drying events caused oxidative release of MeHg to pore waters and resulted in increased net MeHg production likely because available sulfate stimulated the activity of sulfate-reducing bacteria, an important group of Hg-methylating bacteria in peatlands. Rewetting events led to increased MeHg concentrations across the peatland, but concentrations were highest in peat receiving elevated atmospheric sulfate deposition. Dissolved Hg T concentrations also increased in peatland pore waters following drought but were not affected by sulfate loading and did not appear to be directly controlled by dissolved organic carbon mobilization to peatland pore waters. Peatlands are often considered to be sinks for sulfate and Hg T in the landscape and sources of MeHg. Hydrologic fluctuations not only serve to release previously sequestered sulfate and Hg T from peatlands but may also increase the strength of peatlands as sources of MeHg to downstream aquatic systems, particularly in regions that have experienced elevated levels of atmospheric sulfate deposition. DROUGHT INCREASES MERCURY IN PEATLANDS 1697 PUBLICATIONS

show abstract

Section: Discussionmentioning

confidence: 99%

The effects of hydrologic fluctuation and sulfate regeneration on mercury cycling in an experimental peatland

et al. 2015

View full text Add to dashboard Cite

show abstract

“…Given the relatively rapid declines in MeHg concentrations observed by Coleman Wasik et al (2012) once experimental sulfate additions were ceased in this same study wetland, it is hypothesized that the bacterial community structure will also change relatively rapidly with decreased sulfate loading and that changes in bacterial community structure can be related to changes in MeHg accumulation and loss.…”

Section: Introductionmentioning

confidence: 91%

“…Sulfate deposition to aquatic systems such as lakes and wetlands is of particular significance because it has been repeatedly observed to increase levels of methylmercury (MeHg). MeHg is a bioaccumulative neurotoxin that is produced by bacteria in permanently or transiently anoxic aquatic environments (Branfireun et al, 1990;Coleman Wasik et al, 2012;Munthe et al, 2007). Peatlands are a wetland type wherein particularly high production and accumulation of MeHg is often observed in periodically inundated near-surface layers (Mitchell et al, 2008).…”

Section: Introductionmentioning

confidence: 99%

Experimental sulfate amendment alters peatland bacterial community structure

Strickman

Fulthorpe

Wasik

et al. 2016

Science of The Total Environment

View full text Add to dashboard Cite

As part of a long-term, peatland-scale sulfate addition experiment, the impact of varying sulfate deposition on bacterial community responses was assessed using 16S tag encoded pyrosequencing. In three separate areas of the peatland, sulfate manipulations included an eight year quadrupling of atmospheric sulfate deposition (experimental), a 3-year recovery to background deposition following 5years of elevated deposition (recovery), and a control area. Peat concentrations of methylmercury (MeHg), a bioaccumulative neurotoxin, were measured, the production of which is attributable to a growing list of microorganisms, including many sulfate-reducing Deltaproteobacteria. The total bacterial and Deltaproteobacterial community structures in the experimental treatment differed significantly from those in the control and recovery treatments that were either indistinguishable or very similar to one another. Notably, the relatively rapid return (within three years) of bacterial community structure in the recovery treatment to a state similar to the control, demonstrates significant resilience of the peatland bacterial community to changes in atmospheric sulfate deposition. Changes in MeHg accumulation between sulfate treatments correlated with changes in the Deltaproteobacterial community, suggesting that sulfate may affect MeHg production through changes in the community structure of this group.

show abstract

“…13 Considerable output of MeHg to downstream ecosystems can occur when areas of relatively high MeHg production and accumulation are linked to hydrologically connected areas. 14,15 In freshwater wetlands, MeHg production appears limited by sulfate availability, particularly in nutrient poor peatlands, 16,17 and Hg methylation capabilities vary considerably across different wetland types. 18,19 Discrete spatial variations in sulfate loads and redox processes within wetlands are important to the internal spatial patterning of MeHg production.…”

Section: Introductionmentioning

confidence: 99%

Methylmercury production in a chronically sulfate-impacted sub-boreal wetland

Johnson

Mitchell

Engstrom

et al. 2016

Environ. Sci.: Processes Impacts

Self Cite

View full text Add to dashboard Cite

Increased deposition of atmospheric sulfate exacerbates methylmercury (MeHg) production in freshwater wetlands by stimulating methylating bacteria, but it is unclear how methylation in sub-boreal wetlands is impacted by chronically elevated sulfate inputs, such as through mine discharges. The purpose of our study is to determine how sulfate discharges to wetlands from iron mining activities impact MeHg production. In this study, we compare spatial and temporal patterns in MeHg and associated geochemistry in two wetlands receiving contrasting loads of sulfate. Two orders of magnitude less sulfate in the un-impacted wetland create significant differences in acid-volatile sulfide and porewater sulfide; however, dissolved and solid-phase MeHg concentrations and methylation rate potentials (Kmeth) are statistically similar in both wetlands. Permitted mine pumping events flood the sulfate-impacted wetland with very high sulfate waters during the fall. In contrast to observations in sulfate-limited systems, this large input of sulfate to a chronically sulfate-impacted system led to significantly lower potential relative methylation rates, suggesting a predominance of demethylation processes over methylation processes during the sulfate loading. Overall, short-term measurements of methylation and demethylation potential are unrelated to gross measures of long-term MeHg accumulation, indicating a decoupling of short- and long-term process measurements and an overall disequilibrium in the systems. High sulfide accumulation, above ∼600-800 μg l(-1) sulfide, in the sulfate-impacted system lowers long-term MeHg accumulation, perhaps as a result of less bioavailable Hg-S complexes. Although continued research is required to determine how sulfate-limited freshwater wetlands might respond to new, large inputs of high-sulfate runoff from mining operations, chronically impacted wetlands do not appear to continually accumulate or produce MeHg at rates different from wetlands unimpacted by mining.

show abstract

Methylmercury Declines in a Boreal Peatland When Experimental Sulfate Deposition Decreases

Cited by 50 publications

References 56 publications

The effects of hydrologic fluctuation and sulfate regeneration on mercury cycling in an experimental peatland

The effects of hydrologic fluctuation and sulfate regeneration on mercury cycling in an experimental peatland

Experimental sulfate amendment alters peatland bacterial community structure

Methylmercury production in a chronically sulfate-impacted sub-boreal wetland

Contact Info

Product

Resources

About