4 research outputs found
Methylmercury Cycling in High Arctic Wetland Ponds: Controls on Sedimentary Production
Methylmercury (MeHg) is a potent neurotoxin that has
been demonstrated
to biomagnify in Arctic freshwater foodwebs to levels that may be
of concern to Inuit peoples subsisting on freshwater fish, for example.
The key process initiating the bioaccumulation and biomagnification
of MeHg in foodwebs is the methylation of inorganic HgÂ(II) to form
MeHg, and ultimately how much MeHg enters foodwebs is controlled by
the production and availability of MeHg in a particular water body.
We used isotopically enriched Hg stable isotope tracers in sediment
core incubations to measure potential rates of HgÂ(II) methylation
and investigate the controls on MeHg production in High Arctic wetland
ponds in the Lake Hazen region of northern Ellesmere Island (Nunavut,
Canada). We show here that MeHg concentrations in sediments are primarily
controlled by the sediment methylation potential and the quantity
of HgÂ(II) available for methylation, but not by sediment demethylation
potential. Furthermore, MeHg concentrations in pond waters are controlled
by MeHg production in sediments, overall anaerobic microbial activity,
and photodemethylation in the water column
Methylmercury Cycling in High Arctic Wetland Ponds: Sources and Sinks
The sources of methylmercury (MeHg; the toxic form of
mercury that
is biomagnified through foodwebs) to Arctic freshwater organisms have
not been clearly identified. We used a mass balance approach to quantify
MeHg production in two wetland ponds in the Lake Hazen region of northern
Ellesmere Island, NU, in the Canadian High Arctic and to evaluate
the importance of these systems as sources of MeHg to Arctic foodwebs.
We show that internal production (1.8–40 ng MeHg m<sup>–2</sup> d<sup>–1</sup>) is a much larger source of MeHg than external
inputs from direct atmospheric deposition (0.029–0.051 ng MeHg
m<sup>–2</sup> d<sup>–1</sup>), as expected. Furthermore,
MeHg cycling in these systems is dominated by HgÂ(II) methylation and
MeHg photodemethylation (2.0–33 ng MeHg m<sup>–2</sup> d<sup>–1</sup>), which is a sink for a large proportion of
the MeHg produced by HgÂ(II) methylation in these ponds. We also show
that MeHg production in the two study ponds is comparable to what
has previously been measured in numerous more southerly systems known
to be important MeHg sources, such as temperate wetlands and lakes,
demonstrating that wetland ponds in the High Arctic are important
sources of MeHg to local aquatic foodwebs
Data_Sheet_1_Physicochemical Drivers of Microbial Community Structure in Sediments of Lake Hazen, Nunavut, Canada.DOCX
<p>The Arctic is undergoing rapid environmental change, potentially affecting the physicochemical constraints of microbial communities that play a large role in both carbon and nutrient cycling in lacustrine environments. However, the microbial communities in such Arctic environments have seldom been studied, and the drivers of their composition are poorly characterized. To address these gaps, we surveyed the biologically active surface sediments in Lake Hazen, the largest lake by volume north of the Arctic Circle, and a small lake and shoreline pond in its watershed. High-throughput amplicon sequencing of the 16S rRNA gene uncovered a community dominated by Proteobacteria, Bacteroidetes, and Chloroflexi, similar to those found in other cold and oligotrophic lake sediments. We also show that the microbial community structure in this Arctic polar desert is shaped by pH and redox gradients. This study lays the groundwork for predicting how sediment microbial communities in the Arctic could respond as climate change proceeds to alter their physicochemical constraints.</p
Sources of Methylmercury to Snowpacks of the Alberta Oil Sands Region: A Study of In Situ Methylation and Particulates
Snowpacks in the Alberta Oil Sands
Region (AOSR) of Canada contain
elevated loadings of methylmercury (MeHg; a neurotoxin that biomagnifies
through foodwebs) due to oil sands related activities. At sites ranging
from 0 to 134 km from the major AOSR upgrading facilities, we examined
sources of MeHg by quantifying potential rates of MeHg production
in snowpacks and melted snow using mercury stable isotope tracer experiments,
as well as quantifying concentrations of MeHg on particles in snowpacks
(pMeHg). At four sites, methylation rate constants were low in snowpacks
(<i>k</i><sub>m</sub> = 0.001–0.004 d<sup>–1</sup>) and nondetectable in melted snow, except at one site (<i>k</i><sub>m</sub> = 0.0007 d<sup>–1</sup>). The ratio of methylation
to demethylation varied between 0.3 and 1.5, suggesting that the two
processes are in balance and that in situ production is unlikely an
important net source of MeHg to AOSR snowpacks. pMeHg concentrations
increased linearly with distance from the upgraders (R<sup>2</sup> = 0.71, <i>p</i> < 0.0001); however, snowpack total
particle and pMeHg loadings decreased exponentially over this same
distance (R<sup>2</sup> = 0.49, <i>p</i> = 0.0002; R<sup>2</sup> = 0.56, <i>p</i> < 0.0001). Thus, at near-field
sites, total MeHg loadings in snowpacks were high due to high particle
loadings, even though particles originating from industrial activities
were not MeHg rich compared to those at remote sites. More research
is required to identify the industrial sources of snowpack particles
in the AOSR