Mobility and transport of mercury and methylmercury in peat as a function of changes in water table regime and plant functional groups

Haynes, Kristine M.; Kane, Evan S.; Potvin, Lynette R.; Lilleskov, Erik A.; Kolka, Randall K.; Mitchell, Carl P. J.

doi:10.1002/2016gb005471

Cited by 35 publications

(29 citation statements)

References 57 publications

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“…Peat mesocosm experiments suggest that changes in hydrological regimes and shifts in vascular plant communities may have a significant impact on Hg cycling in peatlands (Haynes 2017 ). For example, lower, more variable water tables and the removal of Ericaceae shrubs significantly enhanced inorganic Hg and MeHg mobility in peat pore waters and MeHg export from snowmelt, likely from enhanced peat decomposition and internal regeneration of electron acceptors related to water table changes (Haynes et al 2017 ).…”

Section: Anticipated Impacts From Human and Natural Perturbations Inmentioning

confidence: 99%

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

Obrist

Kirk

Zhang

et al. 2018

Ambio

584

401

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We review recent progress in our understanding of the global cycling of mercury (Hg), including best estimates of Hg concentrations and pool sizes in major environmental compartments and exchange processes within and between these reservoirs. Recent advances include the availability of new global datasets covering areas of the world where environmental Hg data were previously lacking; integration of these data into global and regional models is continually improving estimates of global Hg cycling. New analytical techniques, such as Hg stable isotope characterization, provide novel constraints of sources and transformation processes. The major global Hg reservoirs that are, and continue to be, affected by anthropogenic activities include the atmosphere (4.4–5.3 Gt), terrestrial environments (particularly soils: 250–1000 Gg), and aquatic ecosystems (e.g., oceans: 270–450 Gg). Declines in anthropogenic Hg emissions between 1990 and 2010 have led to declines in atmospheric Hg0 concentrations and HgII wet deposition in Europe and the US (− 1.5 to − 2.2% per year). Smaller atmospheric Hg0 declines (− 0.2% per year) have been reported in high northern latitudes, but not in the southern hemisphere, while increasing atmospheric Hg loads are still reported in East Asia. New observations and updated models now suggest high concentrations of oxidized HgII in the tropical and subtropical free troposphere where deep convection can scavenge these HgII reservoirs. As a result, up to 50% of total global wet HgII deposition has been predicted to occur to tropical oceans. Ocean Hg0 evasion is a large source of present-day atmospheric Hg (approximately 2900 Mg/year; range 1900–4200 Mg/year). Enhanced seawater Hg0 levels suggest enhanced Hg0 ocean evasion in the intertropical convergence zone, which may be linked to high HgII deposition. Estimates of gaseous Hg0 emissions to the atmosphere over land, long considered a critical Hg source, have been revised downward, and most terrestrial environments now are considered net sinks of atmospheric Hg due to substantial Hg uptake by plants. Litterfall deposition by plants is now estimated at 1020–1230 Mg/year globally. Stable isotope analysis and direct flux measurements provide evidence that in many ecosystems Hg0 deposition via plant inputs dominates, accounting for 57–94% of Hg in soils. Of global aquatic Hg releases, around 50% are estimated to occur in China and India, where Hg drains into the West Pacific and North Indian Oceans. A first inventory of global freshwater Hg suggests that inland freshwater Hg releases may be dominated by artisanal and small-scale gold mining (ASGM; approximately 880 Mg/year), industrial and wastewater releases (220 Mg/year), and terrestrial mobilization (170–300 Mg/year). For pelagic ocean regions, the dominant source of Hg is atmospheric deposition; an exception is the Arctic Ocean, where riverine and coastal erosion is likely the dominant source. Ocean water Hg concentrations in the North Atlantic appear to have declined during the last several decades ...

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Section: Anticipated Impacts From Human and Natural Perturbations Inmentioning

confidence: 99%

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

Obrist

Kirk

Zhang

et al. 2018

Ambio

584

401

View full text Add to dashboard Cite

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“…The two target WT profiles were modeled after typical variability, average-WT years ("high WT") and high variability, low-WT years ("low WT"). The mean difference between the high and low-WT positions was approximately 20 cm throughout the experiment (2012-2014; see Potvin et al, 2015 andHaynes et al, 2017 for hydrograph data). These target WT profiles were maintained by a combination of artificial precipitation additions, translucent rain-exclusion covers, and regulated outflow (spring-only, from~25 cm depth, roughly at the acrotelm-catotelm boundary) from each of the bins.…”

Section: Mesocosm Experimentsmentioning

confidence: 99%

“…However, subsequent study has observed mixed evidence for this hypothesis and has shown higher phenolics with declines in WT position in peat mesocosm experiments controlling for plant functional groups and WT position (Dieleman et al, 2016;Romanowicz et al, 2015). In this same experimental framework, the highest phenolic concentrations were observed in treatments with lowered WT positions and sedge vegetation (Haynes et al, 2017). The accumulation of phenolics can further complicate decomposition dynamics through the occlusion of necessary nutrients, particularly nitrogen (e.g., Northup et al, 1995;Schnitzer, 1985).…”

Section: Introductionmentioning

confidence: 99%

Reduction‐Oxidation Potential and Dissolved Organic Matter Composition in Northern Peat Soil: Interactive Controls of Water Table Position and Plant Functional Groups

et al. 2019

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Globally important carbon (C) stores in northern peatlands are vulnerable to oxidation in a changing climate. A growing body of literature draws attention to the importance of dissolved organic matter (DOM) in governing anaerobic metabolism in organic soil, but exactly how the reduction-oxidation (redox) activities of DOM, and particularly the phenolic fraction, are likely to change in an altered climate remain unclear. We used large mesocosms in the PEATcosm experiment to assess changes in peatland DOM and redox potential in response to experimental manipulations of water table (WT) position and plant functional groups (PFGs). WT position and PFGs interacted in their effects on redox potential and quantity and quality of DOM. Phenolics were generally of higher molecular weight and more oxidized with sedges in lowered WTs. Altered DOM character included changes in dissolved nitrogen (N), with higher N:[phenolics] with higher E4:E6 (absorbance ratio λ = 465:665) DOM in the lowered WT and sedge PFG treatments. Conversely, biomolecular assignments to amino-sugars were largely absent from low-WT treatments. Low WT resulted in the creation of unique N compounds, which were more condensed (lower H:C), that changed with depth and PFG. The accumulation of oxidized compounds with low WT and in sedge rhizospheres could be very important pools of electron acceptors beneath the WT, and their mechanisms of formation are discussed. This work suggests the effects of changes in vegetation communities can be as great as WT position in directly and interactively mediating peat redox environment and the redox-activity of DOM. Plain Language Summary Peatlands are important ecosystems in both the global carbon (C)cycle and the Earth's climate system owing to their ability to store vast quantities of C taken from the atmosphere. Peat C stays locked up in these ecosystems largely owing to cool and wet conditions, and as such, these C stores are vulnerable to release back to the atmosphere if the climate or water levels change. Water table level and plant species composition have a combined effect on C and nitrogen (N) cycling in peatlands. We manipulated both factors in an experimental setting composed of 24 large bins into which we put intact peatland miniecosystems. Sedges play a big role in producing N compounds below the peat surface, and this work suggests these compounds can actually be synthesized into larger, less accessible compounds. In addition, activities of sedge roots and other dominant plant communities (such as shrubs in the heath family of plants) may interact in the synthesis of oxidized, larger molecules. These molecules can allow microbes to continue to decompose peat even in the absence of oxygen. This could increase the release of greenhouse gas carbon dioxide to the atmosphere, while reducing inputs of the stronger greenhouse gas methane.

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“…Though peatlands are widely utilized as palaeoclimatological archives (Benoit et al 1998;Biester et al 2007;Talbot et al 2017), Hg retention in peat is not fully understood. As previously mentioned, Hg can for example be re-emitted to the atmosphere after deposition or transported to downstream ecosystems (Osterwalder et al 2017;Haynes et al 2017Haynes et al , 2019. At a peatland chronosequence near Umeå, Sweden, a study suggested that the mobility of Hg in peatlands was increased with Hg methylation, due to lateral runoff or re-emission (likely the latter) (Wang et al 2020).…”

Section: Introductionmentioning

confidence: 95%

Dependence of Total Mercury in Superficial Peat With Nutrient Status: Implications for Stability of Peat as an Archive of Hg Deposition

Smeds¹

2020

Preprint

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Dependence of Total Mercury in Superficial Peat With Nutrient Status: Implications for Stability of Peat as an Archive of Hg Deposition&#160;Jacob Smeds1, Mats B. Nilsson2, Wei Zhu2, Kevin Bishop3[1]Department of Earth Sciences, Uppsala University, Uppsala, Sweden[2]Department of Forest Ecology, Swedish University of Agricultural Sciences, Ume&#229;, Sweden[3]Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden&#160;Although Mercury (Hg) has decreased considerably in the atmosphere during recent decades, this potent neurotoxin still constitutes a threat to ecosystems globally through the Hg stored in soils. The mitigation of the risks related to this legacy Hg was a reason to implement the Minamata Convention. Subsequent work under the convention is dependent on assessments of the Hg stored in the environment. A way of doing this is to study environmental archives of atmospheric deposition such as ice cores, lake sediments, and peatlands. A previous study along a chronosequence of mires along the northern coast of Sweden showed Hg content differing by a factor of 2 and correlating strongly with mire age. This was hypothesized to indicate that differences in minerogenic water supply along the chronosequence influenced the stability of Hg after deposition from the atmosphere to the mire surface. Declining access of minerogenic elements with increasing peatland age results in a less nutrient demanding plant species composition as well as decreasing access to microbial electron acceptors. But that study looked at just one 10 cm layer at a depth with peat ca 50 years old. Here we present a more rigorous test of that hypothesis by presenting the total amount and vertical pattern of Hg accumulation during the last 200 years in the superficial peat along that peatland chronosequence.Eleven peatlands along the northern coast of Sweden near Ume&#229; were sampled. This is an area where isostatic rebound continues to raise the land above the sea level. Triplicate peat cores were collected from both lawns and hummocks, when present. A total of 54 peat cores, each 50 cm deep, were collected and frozen immediately. The cores were then sliced into 2 cm layers, and each slice was analysed for total Hg. Due to the land rising out of the sea, the different peatlands have ages ranging from 100-2000 years since establishment, despite being located within a distance of <10 km. The peatland age correlates with availability of mineral elements and pH. This is due to the fact that the underlying postglacial mineral soil is a source of elements. The distance to the mineral soil increases as peat accumulates with peatland age. Certain elements also leach from the peatlands over time. This documentation of the vertical distribution of Hg in all the peat laid down during the past 200 years in each mire tests the hypothesis that the propensity of Hg to evade back to the atmosphere in this area is related to the amount and composition of inorganic elements.

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Mobility and transport of mercury and methylmercury in peat as a function of changes in water table regime and plant functional groups

Cited by 35 publications

References 57 publications

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

A review of global environmental mercury processes in response to human and natural perturbations: Changes of emissions, climate, and land use

Reduction‐Oxidation Potential and Dissolved Organic Matter Composition in Northern Peat Soil: Interactive Controls of Water Table Position and Plant Functional Groups

Dependence of Total Mercury in Superficial Peat With Nutrient Status: Implications for Stability of Peat as an Archive of Hg Deposition

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