Mercury in the Canadian Arctic Terrestrial Environment: an Update

Home , Devon Ice Cap, Mount Oxford (Nunavut)

STOTEN-16201; No of Pages 13 Science of the Total Environment xxx (2014) xxx–xxx

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Science of the Total Environment

journal homepage: www.elsevier.com/locate/scitotenv

Review Mercury in the Canadian Arctic Terrestrial Environment: An Update

Mary Gamberg a,⁎, John Chételat b, Alexandre J. Poulain c, Christian Zdanowicz d, Jiancheng Zheng e a Gamberg Consulting, Box 30130, Whitehorse, Yukon, Canada Y1A 5M2 b Environment Canada, Ottawa, Ontario, Canada K1A 0H3 c University of Ottawa, Ottawa, Ontario, Canada K1N 6N5 d Uppsala University, Uppsala, Sweden e Natural Resources Canada, Ottawa, Ontario, Canada K1A 0E4

HIGHLIGHTS

• THg and MeHg levels in Arctic snow on land are low, except in coastal areas. • Hg levels in Canadian Arctic glaciers were stable for most of the past century. • THg levels in glaciers show an increasing trend along a north-south gradient. • Water-logged Arctic soils have the potential to methylate mercury. • An Arctic caribou population shows no recent temporal trend in Hg levels.

article info abstract

Article history: Contaminants in the Canadian Arctic have been studied over the last twenty years under the guidance of the Received 17 December 2013 Northern Contaminants Program. This paper provides the current state of knowledge on mercury (Hg) in the Received in revised form 9 April 2014 Canadian Arctic terrestrial environment. Snow, ice, and soils on land are key reservoirs for atmospheric deposi- Accepted 15 April 2014 tion and can become sources of Hg through the melting of terrestrial ice and snow and via soil erosion. In the Available online xxxx Canadian Arctic, new data have been collected for snow and ice that provide more information on the net accu-

Keywords: mulation and storage of Hg in the cryosphere. Concentrations of total Hg (THg) in terrestrial snow are highly var- b -1 Arctic iable but on average, relatively low ( 5ngL ), and methylmercury (MeHg) levels in terrestrial snow are also -1 Mercury generally low (b0.1 ng L ). On average, THg concentrations in snow on Canadian Arctic glaciers are much Snow lower than those reported on terrestrial lowlands or sea ice. Hg in snow may be affected by photochemical ex- Glacier changes with the atmosphere mediated by marine aerosols and halogens, and by post-depositional redistribution Wildlife within the snow pack. Regional accumulation rates of THg in Canadian Arctic glaciers varied little during the past Temporal trends century but show evidence of an increasing north-to-south gradient. Temporal trends of THg in glacier cores indicate an abrupt increase in the early 1990s, possibly due to volcanic emissions, followed by more stable, but relatively elevated levels. Little information is available on Hg concentrations and processes in Arctic soils. Terrestrial Arctic wildlife typically have low levels of THg (b5 μgg-1 dry weight) in their tissues, although caribou (Rangifer tarandus) can have higher Hg because they consume large amounts of lichen. THg concentrations in the Yukon’s Porcupine caribou herd vary among years but there has been no signiﬁcant increase or decrease over the last two decades. © 2014 Elsevier B.V. All rights reserved.

Contents

1. Introduction...... 0 2. TerrestrialHgcycle...... 0 2.1. Generaloverview...... 0 2.2. PhotochemicalHg(II)reductionandemission...... 0 2.3. MeHgdepositionandproduction...... 0

⁎ Corresponding author. Tel.: +1 867 334 3360. E-mail address: [email protected] (M. Gamberg).

3. HginArcticsnowandice...... 0 3.1. HgconcentrationsinArcticsnow...... 0 3.2. Glaciericeandsnow...... 0 3.2.1. Hg concentrations and ﬂuxes...... 0 3.2.2. Temporaltrends...... 0 4. HginArcticsoils...... 0 5. Foodwebs...... 0 6. HginArcticvegetation...... 0 7. Hginterrestrialanimals...... 0 7.1. DistributionofHgintissuesandorgans...... 0 7.2. HginArcticcaribou...... 0 7.3. Hginotherterrestrialanimals...... 0 8. Knowledgegaps...... 0 9. Summary...... 0 Acknowledgements...... 0 References...... 0

1. Introduction deposition and geological weathering (Fig. 1). MeHg is also deposited from the atmosphere although this flux is probably small relative to in- Arctic terrestrial ecosystems support a variety of wildlife including organic Hg (Lehnerr, 2012). Hg(II) in snow, ice, and soil can have several populations of mammals and birds that are important to the culture fates: 1) photochemical reduction to gaseous elemental Hg (GEM) and and traditional diet of northern Aboriginal peoples. Considerable infor- subsequent evasion to the atmosphere, contributing to reemission of mation was collected on Hg in terrestrial mammals and birds from newly deposited Hg (II); 2) transient storage in the snowpack or glacier 1991 to 2003 during Phases I and II of the Northern Contaminants Pro- ice; 3) microbial methylation in soils and possibly also in snow (Larose gram (NCP), with broad geographic coverage across the Canadian Arctic. et al., 2010); 4) transport to aquatic ecosystems via snowmelt, surface In general, Hg levels are below levels of concern for wildlife health in runoff, and erosion; 5) uptake by vegetation, with a subsequent return large mammals such as caribou, moose, wolf and wolverine (Fisk et al., to snow or soils (via throughfall and litterfall) or entering the terrestrial 2003). Terrestrial environments are also important in the regional Hg food chain through herbivores and inevitably returning to soils through cycle because watersheds supply Hg to freshwater and marine ecosys- decomposition. tems. Snow, ice, and soils on land are key reservoirs for atmospheric deposition and, in turn, can become sources of Hg through the melting of 2.2. Photochemical Hg (II) reduction and emission the cryosphere (terrestrial ice and snow) and via soil erosion (Douglas et al., 2012; Stern et al., 2012). A major knowledge gap identified in the Photoreduction and subsequent evasion of volatile Hg0, which is the second Canadian Arctic Contaminants Assessment Report (CACAR II) of main mechanism thought to drive Hg emissions from snow and ice, was the NCP was the lack of information on the fate of Hg following atmo- discussed thoroughly by Steffen et al. (2013a) in an atmospheric con- spheric deposition (Bidleman et al., 2003). Further study was recom- text because of its importance following AMDEs. In soil, Hg (II) originat- mended in order to understand the relationship between Hg ing from atmospheric deposition and geological weathering may also deposition in snow and its incorporation into marine, freshwater, and undergo photochemical reduction and subsequent evasion/ emission terrestrial food webs (Bidleman et al., 2003). Since the CACAR II, several to the atmosphere. Sunlight intensity, temperature and soil moisture important advances have been made regarding the fate of Hg in the ter- may affect the rate of GEM emission from soil (Carpi and Lindberg, restrial environment. New data have been collected for snow and ice that 1998; Schlüter, 2000), while oxidation of GEM by abiotic or microbial provide more information on the net accumulation (flux) of Hg in the processes may reduce net emission from soils. In temperate regions, cryosphere, its storage and post-depositional fate. The monitoring of car- Hg(II) reduction may be driven by sunlight penetrating into the top ibou and moose continued during Phase III of the NCP and included more few millimetres of soil, by the presence of abiotic reductants such as frequent sampling of caribou to increase the statistical power of tempo- humic and fulvic acids, or by reactions mediated by microbes (Gabriel ral trend monitoring for this key terrestrial indicator species. Vegetation and Williamson, 2004). Low emission rates might be expected from (mostly lichen) was also measured for Hg levels to provide information Arctic soils because of lower temperatures, lower annual solar radiation, on uptake at the base of Arctic terrestrial food webs. and lower microbial activity compared to temperate regions. However, The intent of this paper is to evaluate the state of science on Hg in ter- climate change may impact many of the yet unidentified environmental restrial environments of the Canadian Arctic, providing a more conditions that influence soil Hg (II) reduction and evasion in the Arctic. geographically-focussed approach than the recent general circumpolar Measurements made at various sites across Canada, mostly south of 60° review of Douglas et al. (2012). The discovery of Atmospheric Depletion N latitude, revealed a positive correlation between the flux of gaseous Events (AMDEs) (Steffen et al., 2005)hasinfluenced much of the abiotic Hg to the atmosphere and the THg concentration of the mineral research in the Canadian North over the last decade, resulting in the major substrate (Schroeder et al., 2005). Emissions of gaseous Hg from focus of this review on terrestrial snow and ice as repositories of atmo- moss-covered mercuriferous shale at MacMillan Pass in Yukon (mean: spheric Hg. However, the terrestrial environment is generally less studied 1.5 ng m-2 h-1, range: -0.60–10.63 ng m-2 h-1) were considerably higher than the freshwater and marine environments, and this review also than from moss-covered substrate having background levels of geolog- serves to identify important knowledge gaps that should be addressed be- ical Hg near Kuujjuarapik, Quebec (mean: 0.08 ng m-2 h-1, range: cause of their potential role in the cycling of Hg in the Arctic environment. -0.58–1.3 ng m-2 h-1)(Schroeder et al., 2005). Mechanisms of Hg reduction and estimates of emission from terrestrial substrates are significant 2. Terrestrial Hg cycle knowledge gaps in the Arctic Hg cycle.

2.1. General overview 2.3. MeHg deposition and production

Mercury enters the Arctic terrestrial environment primarily as diva- Although pathways for Hg methylation in Arctic terrestrial ecosys- lent inorganic Hg [Hg(II)] via two main pathways: atmospheric tems remain poorly characterized, several novel processes have been

FOREST DYNAMICS BELOW Hg(0) THE ARCTIC TREELINE uptake of atmospheric Hg by foliage possible atmospheric Hg(II) sources of MeHg wet and dry Me2Hg MeHg atmospheric deposition throughfall litterfall

emission from snow/ice Hg(II) Hg(II) soil possible snow methylation evasion MeHg Hg(II) Hg(0)

snow/ice melt transport of Hg(II)/MeHg

bedrock weathering Hg(II) MeHg Hg(II) Hg(0) wetland soil methylation

Hg(II)/MeHg

Fig. 1. Schematic of major transformations and pathways in the Hg cycle for the Arctic terrestrial environment. suggested to explain concentrations of MeHg observed in Arctic snow Concentrations of dimethylmercury measured in Arctic sea (Barkay and Poulain, 2007). The presence of microbial cells, dissolved water and emission estimates based on flux measurements suggest organic substrates, and bioavailable inorganic Hg suggests the possibil- that open water areas in the ocean could be a relevant source to ity that microbes methylate Hg in snow (Barkay and Poulain, 2007; the atmosphere (St. Louis et al., 2007). Some of this volatile Constant et al., 2007; Larose et al., 2010). However, biological activity dimethylmercury may ultimately be deposited as MeHg on terres- is unlikely to be significant in certain circumstances, such as the upper trial snow in coastal areas as a result of photodecomposition. This accumulation zone of large polar glaciers due to the cold temperatures may not, however, be the primary source of atmospherically de- and the lack of mineral nutrients (Price and Sowers, 2004; Hodson posited MeHg in all coastal areas. Prince of Wales Icefield, where et al., 2008; Barkay et al., 2011). the reported MeHg:THg ratio is high, is located next to the North

Table 1 Concentrations and mean annual accumulation rates of THg and MeHg in glacier snow and ﬁrn.

THg

Region / Site Lat. Elev. Years N THg λSWE FTHg Data sources (°) (m) (ng L-1) (m a-1) (μgm-2 a-1) mean ± 1σ mean ± 1σ

Ellesmere Island Mt Oxford Icefield 82 1680 ~66 166 0.38 ± 0.30 0.15 0.06 ± 0.03 Zheng et al. (2014) Agassiz Ice Cap 81 1670 ~26 118 0.66 ± 0.45 0.11 0.07 ± 0.02 Zheng et al. (2014) John Evans Glacier 79 N800 b1 15 0.60 ± 0.21 0.17 ~0.10 St. Louis et al. (2005) Prince of Wales Icefield 78 N1200 b1 29 0.31 ± 0.12 0.30 ~0.09 St. Louis et al. (2005) Devon Island Devon Ice Cap 77 1800 ~10 43 0.68 ± 0.33 0.24 ~0.16 C. Zdanowicz, unpublished data Baffin Island Penny Ice Cap 67 1860 ~40 366 1.24 ± 3.81 0.40 0.11 ± 0.05 Zdanowicz et al. (2013, 2014 [this issue])

MeHg

Region / Site Lat. Elev. Years N MeHg λSWE FMeHg Data sources (°) (m) (ng L-1) (m a-1) (μgm-2 a-1) mean ± 1σ mean ± 1σ

Ellesmere Island John Evans Glacier 79 N800 b1 15 0.06 ± 0.01 0.17 ~0.01 St. Louis et al. (2005) Prince of Wales Iceﬁeld 78 N1200 b1 29 0.09 ± 0.06 0.30 ~0.03 St. Louis et al. (2005) Devon Island Devon Ice Cap 77 1800 ~10 16 0.02 ± 0.01 0.24 b0.01 C. Zdanowicz, unpublished data Bafﬁn Island Penny Ice Cap 67 1860 ~40 158 0.11 ± 0.07 0.40 0.04 ± 0.03 Zdanowicz et al. (2013, 2014 [this issue]

Note: Values of FTHG and FMeHg for John Evans Glacier and Prince of Wales Iceﬁeld were estimated using λSWE data for the highest parts of the accumulation zone (Sharp et al., 2002; Mair et al., 2009).

Water polynya, a year-round source of marine aerosols (St. Louis 3. Hg in Arctic snow and ice et al., 2005). However, the flux of primary sea-salt aerosols in snow, as represented by chloride ions, is comparable on Prince of 3.1. Hg concentrations in Arctic snow Wales Icefield and on Devon Ice Cap (Kinnard et al., 2006)even though the proportion of MeHg in snow at these sites is strikingly Terrestrial snow THg concentrations ranged three orders of magni- different (Table 1). This suggests that atmospheric MeHg deposi- tude, from 0.3 to 156 ng L-1 at three Canadian Arctic sites (Fig. 2). tion in snow at these sites is controlled by some other factor(s) Although maximum observed concentrations were high, average con- than, or in addition to, marine aerosols. centrations (where available) were relatively low (b5ngL-1) compared Other possible mechanisms for MeHg accumulation that have not to snow over sea ice in the circumpolar Arctic (see Table 2.9 in Munthe been confirmed are sunlight-induced methylation in the presence of la- et al., 2011) and snow at mid-latitudes (b1toN 50 ng L-1; see for exam- bile organic matter in snow, atmospheric methylation by abiotic reac- ple Table 1 in Nelson et al., 2008,andTable3inDurnford et al., 2012). tions (Hammerschmidt et al., 2007), or microbial methylation on Less information is available for MeHg in terrestrial snow. Based on aerosols in the atmosphere (Barkay and Poulain, 2007). studies from Cornwallis Island, Alert, and Kuujjuarapik, snow MeHg Water-logged terrestrial soils are also potential sites for MeHg pro- concentrations average b 0.1 ng L-1and generally range from below de- duction in the Arctic. In temperate environments, wetlands can be tection limit to 0.2 ng L-1 (Dommergue et al., 2003a; Lahoutifard et al., major sources of MeHg, which is formed by the activity of sulphate- 2005; St. Louis et al., 2005, 2007), but can reach as high as 0.7 ng L-1, and iron-reducing bacteria (Fleming et al., 2006; Gilmour et al., 1992). as observed in Kuujjuarapik (Constant et al., 2007). As with THg, Loseto et al. (2004) conducted laboratory incubations of Arctic wetland MeHg concentrations also vary with depth in the terrestrial snowpack, soils at typical Arctic summer temperatures (4–8 °C) and found that and the middle stratum or depth hoar were sometimes found to have MeHg concentrations increased up to 100-fold after 30 days. While a higher concentration than the surface (Dommergue et al., 2003a; St. sulphate-reducing bacteria are dominant MeHg producers in temperate Louis et al., 2005, 2007). anoxic environments, the genes responsible for sulphate reduction The high variability in Hg concentrations in Arctic snow reflects could not be detected in the Arctic study sites. This suggested either complex processes and transformations within the snow pack. Freshly an issue with gene detection or that sulphate reducers are not the deposited Hg on snow is highly reactive (Lalonde et al., 2002), and a most dominant methylators in Arctic wetlands. Oiffer and Siciliano portion (20-50%) of the Hg deposited during AMDEs is quickly returned (2009) reported that Hg was mostly associated with natural organic to the atmosphere within 24 hours of deposition through photoreduc- matter with low sulphide content in an Arctic wet sedge meadow. tion of Hg(II) to GEM within the surface snowpack (see Table 1 in They observed methylation after inorganic Hg was amended to the Durnford et al., 2012, for a range of estimates). Typically, about 80% of soil, suggesting that there is potential for soil production of MeHg dur- newly deposited Hg is lost from the snow surface two or more days ing spring melt. after an AMDE (Munthe et al., 2011). The presence of halogens in The decomposition of MeHg reduces its concentration in snow and snow may act to retain Hg, and indeed, elevated snow Hg concentra- soils. While demethylation rates have not been measured in Arctic ter- tions are more often found in coastal environments where deposition restrial environments, this process may occur via abiotic or microbial of sea salt can be expected (Douglas and Sturm, 2004; Poulain et al., pathways (Barkay and Poulain, 2007). Lahoutifard et al. (2005) ob- 2007a; St. Louis et al., 2007). Conversely, these higher concentrations served a decrease in snowpack MeHg concentration during spring may occur primarily because AMDEs are a result of photochemical reac- time which was negatively correlated with temperature. Constant tions involving marine halogens and ozone. Burial through snow accu- et al. (2007) observed rapid demethylation of snow MeHg at night mulation, sublimation, condensation, and ice layer formation also which ruled out photodecomposition at that site. promote retention of Hg in the snowpack (Douglas et al., 2008).

Kuujjuarapik, QC (J) (38)

Kuujjuarapik, QC (I) (24)

Cornwallis Island, NU (H) (3)

Cornwallis Island, NU (G) (7)

Cornwallis Island, NU (F) (19)

Cli Lake, NT (E) (14)

Alert, NU (D) (20)

Alert, NU (B,C) (31)

Alert, NU (A) (na)

0.1 1 10 100 Log THg concentration in snow (ng L-1)

Fig. 2. Ranges of THg concentrations measured in snow from terrestrial sites in the Canadian Arctic (excluding glaciers). Concentrations are presented on a logarithmic scale. Where available, mean concentrations are represented by a line in the bar, and sample sizes are provided in parentheses. References: A = Steffen et al. (2002);B=St. Louis et al. (2005);C=St. Louis et al. (2007);D=Cobbett et al. (2007);E=Evans and Lockhart (1999);F=Lahoutifard et al. (2005);G=Poulain et al. (2007a);H=Lu et al. (2001);I=Dommergue et al. (2003a);J= Constant et al. (2007).

While deposition occurs at the snow surface, Hg can also be from catchment drainage. Glaciers can also preserve a temporal se- redistributed within the accumulated snow. Migration of GEM within quence of net atmospheric Hg deposition that can be reconstructed by the snowpack and subsequent oxidation can result in accumulation of the analysis of cores. The degree of preservation of the sequence and Hg within deeper layers (Dommergue et al., 2003b; Faïn et al., 2006). the temporal resolution that can be attained depend on snow accumu- Melt events may redistribute Hg toward deeper layers away from the lation and summer surface melt rates (Faïn et al., 2008; Zdanowicz et al., high energy surface of the snowpack. Concentrations in snowpacks are 2013). commonly highest in the surface layer (Dommergue et al., 2003a; St. Firn is snow that has survived summer melt without being con- Louis et al., 2007), but the middle stratum or depth hoar—alayerof verted to ice. It is the intermediate state between seasonal snow and large crystals at the base of the snowpack—can also be dominant reser- glacier ice, and its density increases with depth of burial from ~400 to voirs of Hg in some settings. Therefore, post-depositional processes over ~920 kg m-3 (glacier ice). In many glaciers, firn layers are interspersed the entire depth of the snowpack may influence Hg accumulation. with discrete layers or lenses of infiltration ice, which are formed by the refreezing of meltwater during summer (e.g., Zdanowicz et al., 3.2. Glacier ice and snow 2013). Dynamic, photochemically-driven exchanges between air and snow affect the distribution of Hg in glacier firn and interstitial air Glacier snow and firn offer several advantages for monitoring atmo- down to 2 m. However, below this depth, GEM levels in firn air are spheric Hg deposition compared to other environmental matrices. Any close to mean atmospheric concentrations, and the THg concentrations Hg found in snow is almost exclusively from the atmosphere, provided in firn layers show little variability (Faïn et al., 2006, 2008). Thus, hourly samples are collected in the accumulation zone of glaciers where contri- to seasonal changes in the GEM content of the snowpack and firn are ap- butions from local contamination sources are minimized. This is not the parently smoothed below ~ 2 m. On Arctic glaciers with steeper densifi- case for lake sediments, for example, where Hg can also be supplied cation gradients and lower firn permeability, this depth limit is probably

(a) (b)

Fig. 3. Mean THg (panel a) and MeHg (panel b) and annual accumulation rates of THg (panel c) and MeHg (panel d) in Canadian Arctic glacier snow and ﬁrn. JEG = John Evans Glacier; PofW = Prince of Wales Iceﬁeld. Data from St. Louis et al. (2005), Zdanowicz et al. (2013, 2014 [this issue]), Zheng et al. (2014).

(Baffin Island). Other available THg and MeHg data come from Prince glaciers follows a spatial pattern broadly similar to that of FTHg,and of Wales Icefield and John Evans Glacier on central Ellesmere Island that pattern has been linked to southerly advection of polluted air (St. Louis et al., 2005) but these span less than a full year of deposition. from the eastern United States and Canada (Goto-Azuma and Koerner, Together, these data provide a picture of the present-day spatial varia- 2001). tions of Hg and MeHg accumulation on Canadian Arctic glaciers. Glacier estimates of FTHg can be compared to Hg accumulation rates Mean THg concentrations in snow and firn at all glacier sites range inferred from other natural media reported in the literature, in particu- from 0.31 to 1.24 ng L-1 (Table 1). The lowest mean concentrations lar lake sediments and peat (Table 2). Present-day Hg accumulation (≤0.5 ng L-1) are found on Ellesmere Island at Prince of Wales and rates in glacier firn are lower, by one or two orders of magnitude, than Mount Oxford icefields, and the highest (N1ngL-1) on Penny Ice Cap in lake sediments and peat, even when the latter are corrected for fac- (Fig. 3a). Given the different sample sizes, and the high variance in the tors such as catchment size or sediment focusing. Several reasons data (relative standard deviations N 20%), some of the inter-site differ- could account for these differences. These may include diagenetic ef- ences in Table 1 may not be statistically meaningful, for example those fects in peat, greater retention of Hg in peat and/or sediments (through between John Evans Glacier and Penny Ice Cap. On average, THg concen- the formation of organic complexes) as compared to snow, geogenic trations on Canadian Arctic glaciers are much lower than those reported contributions of Hg from lake catchment runoff, greater contributions in snow surveys of Arctic marine or lowland terrestrial environments of AMDEs to Hg levels in snow meltwater at low-elevation and/or coast- (see Durnford and Dastoor, 2011, for a review), and also generally al sites, and climatically-modulated magnification of Hg deposition in lower than those in mid-latitude mountain glaciers (~1-40 ng L-1; lake sediments, for e.g. through increased algal scavenging and in- Schuster et al., 2002; Eyrikh et al., 2003; Wang et al., 2008). THg concen- creased sedimentation rates (see Goodsite et al., 2013, and references trations in spring surface snow at coastal and marine Arctic sites are therein, for a review). often an order of magnitude higher, and can exceed 100 ng L-1. Elevated Near-surface snow layers sampled on glaciers in late winter or early Hg concentrations in surface snow in spring may result from AMDEs, spring commonly contain THg levels considerably greater than in but as several studies have shown (e.g., Kirk et al., 2006), much of it deeper layers (e.g., Faïn et al., 2008). This was observed at the Canadian (possibly N 80 %) may be rapidly re-emitted back to the atmosphere, Arctic glacier sites, although the magnitude of near-surface enrichments such that the apparent disparity with Hg measurements from glacier varied considerably between sites. The higher THg in surficial snow are snow and firn may not be as large as it seems. thought to reflect the transient deposition of reactive gaseous Hg, which There are fewer MeHg data available from glaciers than for THg in the Arctic is attributable to AMDEs (Steffen et al., 2008). At most gla- (Table 1). Where measured, mean MeHg concentrations in glacier cier sites in the Canadian Arctic, the enrichment is restricted to the up- snow and firn vary from 0.02 ng L-1 on Devon Ice Cap to 0.11 ng L-1 permost few cm or tens of cm in the snowpack. The contribution of on Penny Ice Cap (Fig. 3b). The available data are presently too limited near-surface snow layers to the THg burden stored annually in firn is to identify geographical patterns with any confidence. There are re- thought to be relatively small: at least half, and typically more, of the markably large inter-site differences in the proportion of THg as THg that ends up in firn storage is actually found in the summer or au- MeHg, varying from 3% on Devon Ice Cap to 38% on Prince of Wales tumn snow layers, which usually make up most of the total annual accu- Icefield. At Station Nord, Greenland, Ferrari et al. (2004) found compa- mulation. On Penny Ice Cap, for example, the THg in winter and early rably large variations in the MeHg:THg ratio in snow (1 to 16 %), spring layers is estimated to be b 25 % of the annual burden which resulted from post-depositional changes in THg levels by photol- (Zdanowicz et al., 2013). At this site, and possibly at others of compara- ysis in near-surface snow. ble latitude, atmospheric Hg deposition to snow may be predominantly For each of the glaciers in Table 1, the accumulation rate of THg in occurring during the warmer and moister half of the year. The contribu- snow, or net flux FTHg, was calculated from the mean THg concentration tion of AMDE-deposited THg in glacier snow could be proportionally in snow and firn samples, and the mean snow accumulation rate, larger at the colder and drier northernmost sites such as Agassiz Ice Cap. expressed in meters of snow water equivalent (λSWE). Values of λSWE Accumulation rates of Hg on Canadian Arctic glaciers can also be for recent decades were obtained from published studies or estimated compared with measurements of direct wet deposition and with atmo- using seasonal indicators (e.g., oxygen stable isotopes) and/or reference spheric transport model simulations for the Arctic (Table 2). Glacier es- markers in firn and ice cores such as the 1963 peak in radioactivity. timates of FTHg are closer to wet deposition rates measured at latitudes Where available, glacier mass balance and ice-core data indicate that re- of 58–68° N than to accumulation rates inferred from peat and sedi- gional λSWE have varied little during the past century. For Penny Ice Cap, ments at polar latitudes. The comparison with simulation outputs the THg data were weighted to take into account variations in firn den- shows that the range of model-projected total (wet and dry) Hg depo- sity (Zdanowicz et al., 2014 [this issue]). Flux estimates obtained in this sition rates over the Canadian Arctic islands (~2–12 μgm-2 a-1) exceeds way correspond to the accumulation (burial) rate of THg in glacial firn net deposition rates inferred from glacier snow and firn by at least one after any post-depositional modifications have taken place (e.g., by pho- order of magnitude, even in simulations that neglect the fast oxidation tolytic re-emission). pathway for GEM associated with AMDEs. The usefulness of such com- Results of flux calculations (Table 1) reveal some regional parisons for Arctic Canada is at present somewhat limited by the spatial 2 differences, with individual mean values of FTHg varying from coarseness of existing models (150 km for DEHM, 1° x 1° for GRAHM, 0.06 μgm-2 a-1 on Northern Ellesmere Island to 0.16 μgm-2 a-1 on 2.5° x 2.5° for MSCE-Hg). Reasons for the large discrepancies between Devon Ice Cap (Fig. 3c). The flux values for John Evans Glacier and Prince model-simulated Hg deposition rates and those inferred from glacial ar- of Wales Icefield are based on less than a full year of snow accumulation, chives are not altogether clear at present, and may be partly due to

Table 2 Annual net Hg deposition rates at northern high latitudes inferred from environmental sampling media.

-2 -1 Region Sampled medium Period FTHg (μgm a ) Data sources Southern Baffin Island (67° N) Glacier snow & firn Last ~40 years 0.1 Zdanowicz et al. (2014 [this issue]) Canadian High Arctic (77-82° N) Glacier snow & firn Last ~66 years ≤0.1 Zheng et al. (2014) Central Baffin Island (73° N) Lake sediments Last ~100 years 6 to 12 Cooke et al. (2012) Canada (51 - 64° N) Lake sediments Last ~10 years 5 to 18 Muir et al. (2009) Canada (66 - 83° N) Lake sediments Last ~10 years 15 to 39 Muir et al. (2009) Greenland (66 - 67° N) Lake sediments Last ~10 years 5 to 10 Bindler et al. (2001) Alaska (68° N) Lake sediments1 Last ~10 years 2 to 5 Fitzgerald et al. (2005) Svalbard, Norway (78° N) Lake sediments Last ~100 years 9 to 15 Jiang et al. (2011) Norway (58 - 69° N) Peat Last 100 years 1 to 7 Steinnes et al. (2003) Sweden (57 - 59° N) Peat Last ~10 years 5 to 20 Bindler (2003)

Annual gross Hg deposition rates inferred from measured wet deposition

-2 -1 Region Sampled medium Period FHgT (μgm a ) Data sources Churchill, Manitoba [58° N) Precipitation 2007-2008 0.5 to 0.8 Sanei et al. (2003) Churchill, Manitoba [58° N) Precipitation 2006 1.4 Outridge et al. (2008) Pallas, Finland [67° N) Precipitation 1996 2.1 Berg et al. (2001) Toolik LTER, Alaska [68° N) Precipitation 1988 0.9 to 2.1 Fitzgerald et al. (2005)

Annual Hg deposition rates projected by atmospheric transport models

2 -2 -1 Region Model Period FHgT (μgm a ) References North American Arctic DEHM, GLEMOS, GRAHM 1990-2005 3.5 to 5.2 Goodsite et al. (2013) Canadian Arctic islands GRAHM, with AMDE 2001 1.5 to 6 Dastoor and Davignon (2009) DEHM, with AMDE 2001 9 to 12 Christensen et al. (2004) DEHM, no AMDE 2001 3 to 6 Christensen et al. (2004) MSCE-Hg, with AMDE 1996 5 to 12 Travnikov and Ryaboshapko (2002) MSCE-Hg, no AMDE 1996 2 to 5 Travnikov and Ryaboshapko (2002)

Notes: 1Corrected for soil input. 2GLEMOS = Global EMEP, Multi-media Modeling System; GRAHM = Global/Regional Atmospheric Heavy Model; DEHM = Danish Eulerian Hemispheric Model; MSC-E: EMEP Meteorological Synthesizing Centre East model for Hg.

spatial scaling issues, as discussed by Goodsite et al. (2013). Clearly, fur- 3.2.2. Temporal trends ther work is required to validate model predictions against measure- Multi-decadal temporal trends of THg were reconstructed from ments of Hg deposition in the Canadian Arctic. snow, firn and ice collected at three sites on Canadian Arctic ice caps: Agassiz Ice Cap and Mount Oxford Icefield on northern Ellesmere Island, and Penny Ice Cap on southern BaffinIsland(Fig. 4). Strict proto- cols were used for field and laboratory procedures to avoid potential sample contamination and ensure analytical accuracy and precision (Zdanowicz et al., 2013, 2014 [this issue]; Zheng et al., 2014). Age dating of the samples was based on multiple parameters, including ionic chemistry, estimated snow accumulation rates, references to dated volcanic eruptions, and correlations with chronologies already established in other ice caps in the Canadian Arctic. Accuracy of age dating varied from ± 0.5 years for the Agassiz and Mount Oxford samples to ± 5 years for those from Penny Ice Cap. The poorer dating accuracy at Penny Ice Cap is largely the result of much greater summer melt and percolation at this site, which can offset depositional features in the firn by several years (Zdanowicz et al., 2012). Fig. 4 compares the historical profiles in THg concentration reconstructed at the three glacier sites. The period of overlap is approximately 30 years long (~1980-2009). The Agassiz and Mount Oxford Ice Cap records, which were dated independently, show excellent agreement. The THg concentrations at Mount Oxford are approximately half those at Agassiz Ice Cap, presumably due to the differences in snow accumulation rates between these two sites (Table 1). The Agassiz record, which spans ~66 years, shows relatively constant THg concentrations in snow through the earlier part of the 20th century, followed by an increase between ~1990 and 2000. These trends differ from those reconstructed from GEM in interstitial firn air at Summit, Greenland (Faïn et al., 2008), which suggests the latter record cannot directly predict trends in atmospheric Hg deposition in High Arctic snow. The Agassiz THg record also lacks a post-1970s decline such as that reported in fil- Fig. 4. Comparison of temporal trends of THg concentrations in ice and snow at Agassiz Ice tered aerosol Hg collected in Resolute (Li et al., 2009). These results sug- Cap, Mount Oxford Icefield and Penny Ice Cap (Zdanowicz et al., 2013, 2014 [this issue]; Zheng, 2014 [this issue]) with direct measurements of atmospheric GEM at Alert by Envi- gest a greater heterogeneity in THg deposition trends across the Arctic ronment Canada. than was previously assumed (e.g., Goodsite et al., 2013).

All three THg records from Canadian Arctic glaciers share a common time frame of 5,900 to 800 calibrated years before present (Givelet feature: an abrupt increase in THg concentration that occurred in the et al., 2004). Distributions of conservative lithogenic elements in the early 1990s and was followed by a multi-year period of sustained THg cores were not correlated with the Hg profiles, suggesting that atmo- levels greater than those prior to the increase. The close similarity be- spheric deposition rather than mineral dust input was the source of tween the Agassiz and Mount Oxford records shows that this feature Hg accumulation (Giveletetal.,2004). A pre-anthropogenic atmospher- is not an artefact, and flux calculations confirm that THg deposition in ic deposition rate of approximately 1 μgm-2 a-1 (inferred from the snow did increase significantly at both sites during the corresponding peat cores) is consistent with historical fluxes observed in peat from interval. Dating of the Penny Ice Cap record is less precise, but Greenland and also from bogs at temperate latitudes (Givelet et al., the early 1990s THg increase recorded in this core is very likely 2003; Shotyk et al., 2003). The authors of the Bathurst Island study con- synchronous, within dating error, to that observed in the two Ellesmere cluded that, before the Industrial Era, the Arctic was not a more impor- Island records. The initial THg increase on Penny Ice Cap (max. THg = tant sink for global atmospheric Hg than temperate latitudes because of 46 ng L-1) is ~10 times greater than that recorded on Agassiz Ice Cap the similarity in Hg accumulation rates in peat from those two zones. It (max. THg = 3.8 ng L-1). A plausible account for this feature is that it should be noted that the use of Arctic peat as an environmental archive represents Hg fallout associated with the 1991 Icelandic eruption of of Hg deposition is controversial because of potential effects of annual Hekla, which left a clear Hg spike (730 ng L-1) in snow in central Green- freeze-thaw cycles on the long-term stability of the accumulated Hg land (Gabrielli et al., 2008). The lower magnitude of the THg peaks in (Bindler et al., 2005; Shotyk et al., 2005). the Agassiz and Mount Oxford records, compared to those in Greenland and on Penny Ice Cap, likely reflect the exponential decrease in volcanic 5. Food webs fallout rates at increasing distance from the vent. The post-1990 period of sustained elevated THg deposition in the Agassiz and Mount Oxford Lichens, which are an important food for many Arctic herbivores, records extended until ~2000. On Penny Ice Cap, it was seemingly have no root system and accumulate Hg mainly from the atmosphere shorter, but as this record may be affected by post-depositional elution, (Estrade et al., 2010). Below the tree line, foliage of trees and shrubs the difference in timing may be apparent only. Reasons for the sustained also accumulates Hg mainly from atmospheric deposition directly higher THg concentrations in High Arctic snow during the decade 1990- onto leaves rather than through uptake by roots (Ericksen et al., 2003; 2000 observed in Arctic glacier cores are at present unclear, and further Graydon et al., 2009; Grigal, 2002). Thus, vegetation can play an impor- investigations are needed to better understand these dynamics. tant role in scavenging Hg and increasing its flux to snow and soils via The longest record of direct, continuous atmospheric Hg measure- throughfall and litterfall (Graydon et al., 2008; Poulain et al., 2007b). ments (GEM) in the Arctic comes from Alert and now spans more In this way, Hg in vegetation may be returned to the snow or soil, or than two decades (Cole and Steffen, 2010; Cole et al., 2013). As shown may enter the terrestrial food web through herbivorous animals con- in Fig. 4, there is clear evidence from Canadian Arctic glaciers of large suming the vegetation. intra-decadal variations in THg deposition during the 1990s and Terrestrial food webs in the Arctic generally consist of three trophic 2000s, but the Alert GEM record only shows minor declining trends of levels: primary producers (vegetation), herbivores, and carnivores or -0.6 to -0.9% per year during this period. The lack of correspondence scavengers. Information is currently lacking on the transfer of Hg between these records, and with reconstructed GEM variations in through terrestrial food webs in the Canadian Arctic, although it is likely Greenland (Faïn et al., 2008), highlights the complexity of predicting that biomagnification occurs between consumers and their diet. Hg deposition rates from gaseous measurements only. Clearly, long- Rimmer et al. (2010) showed a pattern of Hg biomagnification at suc- term variations in net THg accumulation in snow must also be con- cessive trophic levels in a southern montane forest food web, with the trolled by factors other than GEM levels and snow accumulation. highest concentrations observed in raptors. Evers et al. (2005) found a These factors may include changing levels of other atmospheric species, similar pattern in avian freshwater communities in northeastern such as Arctic Haze constituents, marine halogens or sea salts, which can North America and also noted high levels of Hg in insectivorous birds. participate in air-snow transfer mechanisms (Steffen et al., 2013b). Given these patterns of biomagnification, it would be expected that the highest levels of Hg occur in top trophic level consumers in the Arc- 4. Hg in Arctic soils tic as well. A typical Arctic terrestrial food web consists of lichens, barren-ground caribou, and wolves. While caribou have higher THg Few published studies currently exist on Hg in Canadian Arctic soils. concentrations than lichens (Gamberg, 2009, 2010), wolves do not nec- The most comprehensive investigations were conducted on wetland essarily have correspondingly higher concentrations (Gamberg and soils of Cornwallis Island (Loseto et al., 2004)andwetsedgetundraon Braune, 1999). For example, dry weight (dw) concentrations of THg in Devon Island (Oiffer and Siciliano, 2009). Wetland soils typically had caribou kidney averaged 2.8 ± 1.7 μgg-1 while those reported for low THg concentrations, averaging 46 ng g-1 and ranging from wolf kidney from several Canadian Arctic regions averaged 1.0 ± 10–250 ng g-1 (Loseto et al., 2004). The proportion of THg as MeHg 0.7 μgg-1 (Gamberg and Braune, 1999). Arctic fox (Alopex lagopus)in was also low (b1%), and MeHg concentrations averaged 0.07 ng g-1. Alaska also showed similar levels of kidney THg (Dehn et al., 2006). Higher MeHg concentrations ranging from 0.34–3.07 ng g-1 were ob- This apparent lack of biomagnification may be due to some wolves feed- served in sedge meadow soils on Devon Island (Oiffer and Siciliano, ing on moose and small mammals, which tend to have considerably 2009), concentrations declining during the summer study period. lower Hg body burdens than caribou (Gamberg et al., 2005a). Cores of coastal permafrost soils were collected along the Beaufort Recent studies have shown that terrestrial food webs in Arctic coast- Sea at Tuktoyaktuk in the Northwest Territories and on Herschel Island, al areas may receive input of Hg from marine resources. Arctic foxes in King Point, and Komakuk Beach along the Yukon coast (Leitch, 2006). northern Manitoba feed in the marine environment during years with Concentrations of THg ranged from 26–303 ng g-1 at different depths low lemming abundance (Roth, 2003). In Alaska, satellite-tagged foxes in sectioned permafrost cores, and median values ranged from have been observed to travel long distances over sea ice, foraging for 61–114 ng g-1 for each core. These concentrations were generally higher several months at a time (Pamperin et al., 2008). Wolves will also feed than the THg in frozen peat cores from Bathurst Island, which averaged on marine mammal carcasses along the Alaskan coastline (Watts et al., b 50 ng g-1 (Givelet et al., 2004). The flux of Hg from coastal erosion of 2010). While no investigations have been conducted in Canada, re- permafrost soils is a significant source to the Arctic Ocean (Outridge search in the circumpolar Arctic has shown that Arctic foxes linked to et al., 2008). a marine-based diet feed at a higher trophic position and have higher Peat deposits from Bathurst Island (Nunavut) indicated a relatively tissue Hg (Bocharova et al., 2013) and organic contaminant (Fuglei constant accumulation rate of THg of 0.5–1.5 μgm-2 a-1 across a long et al., 2007) levels than those with more terrestrial-based feeding.

The role of insects and insectivores in the trophic transfer of Hg This pattern is likely related to the dominant form of Hg in the diet remains poorly resolved in Arctic terrestrial food webs. Among Arctic —inorganic Hg versus MeHg—and differences in detoxification mech- mammals, only shrews and bats eat appreciable amounts of insects, anisms among species. Muscle tissue of caribou and moose mainly but the latter is an obligate insectivore in this environment. Arctic contains MeHg, which accounts for about 75% and 90% of THg, re- birds, however, have a much greater diversity in diet. In the boreal spectively (M Gamberg, unpublished data). These proportions are Arctic, some passerines (warblers, thrushes, vireos and others), hum- somewhat lower than the average of 100% reported for muscle tissue mingbirds, woodpeckers, and raptors (kestrels and shrikes) eat in- in marine mammals (Wagemann et al., 1997) and are likely related to sects to varying degrees while nightjars, flycatchers, and swallows the form of Hg in the diet. are aerial insectivores that eat almost exclusively flying insects. Rails, dippers, and blackbirds eat mainly aquatic larvae of insects. In- 7.2. Hg in Arctic caribou sects could potentially represent an important route of Hg exposure to some Arctic wildlife. Mean renal concentrations ranged from 0.30 μgg-1 THg dw in the woodland Klaza caribou herd (Yukon) to 6.2 μgg-1 in the barren- 6. Hg in Arctic vegetation ground Beverly herd (NT) (Fig. 5). Differences in THg concentrations among caribou herds may be due to atmospheric Hg deposition patterns Mercury accumulation in plants has received relatively little study in across the Arctic (Dastoor and Larocque, 2004), differences in Hg dy- the Canadian Arctic. Two recent investigations, one in Yukon (Gamberg, namics within the abiotic environment, including marine influences 2009) and one in Nunavut (Choy et al., 2010), both found that lichens (Steffen et al., 2008) and/or differing proportions of diet consisting of li- had the highest concentrations of THg among all vegetation analyzed, chens (Larter and Nagy, 2000). The winter diet of Peary caribou contains ranging from 49 ng g-1 in Yukon to 231 ng g-1 in Nunavut. Although very little lichen and is largely made up of grasses, sedges, and forbs concentrations were generally higher in lichens from the Nunavut (Larter and Nagy, 1997; Parker, 1978; Shank et al., 1978). Therefore, site, this variation may be due to differences in species collected from lower concentrations of Hg were expected in these caribou, and it is each location. Studies in Nunavut (Chiarenzelli et al., 2001)andYukon not clear why their THg levels were relatively high (Fig. 5). Seasonal (Gamberg, 2009) measured the same concentration of THg (72 ng monitoring of the Porcupine caribou herd in Yukon revealed that g-1) in the curled snow lichen (Flavocetraria cucullata), but twice as spring-collected females had higher renal concentrations of THg than much THg in a closely related species (Flavocetraria nivalis) from the fall-collected females (Gamberg, 2006). Seasonal variation in kidney Nunavut site. Crête et al. (1992) found that concentrations of THg in li- size has been used to explain differences in cadmium concentrations chens increased eastward in Quebec and were higher in tundra biomes in caribou. Kidneys are generally at their largest in the fall (Crête et al., than forest. The authors hypothesized that lichens on the tundra are ex- 1989; Gamberg and Scheuhammer, 1994), and would therefore show posed to more Hg deposition due to the absence of trees and the rarity a lower Hg concentration even if the absolute amount of Hg within of vascular plants that could intercept particulate deposition. Flowering the kidney remained the same. Seasonal variation in diet may also plants in the Arctic tend to have lower THg than lichens while sedges play a role. A model estimating Hg intake by Porcupine caribou and willows show the lowest concentrations (Choy et al., 2010; (Gamberg, 2009) indicated that Hg intake is highest in the late fall and Gamberg, 2009). winter when lichens make up most of the diet and is lowest in the sum- Carignan and Sonke (2010) reported that THg concentrations in tree mer months when the caribou are feeding more on grasses, sedges, and lichens in Quebec were highest near Hudson Bay (up to 2.1 μgg-1 dw) forbs. There is a potential spike of Hg intake in the fall when mushrooms and decreased along a gradient inland in association with lower tissue are available, but this modelling result needs to be confirmed. concentrations of the halogens bromine, chlorine, and iodine. They con- Pollock et al. (2009) found a different seasonal trend for George cluded that the high THg measured in tree lichens close to Hudson Bay River caribou in Labrador, which had lower renal THg concentrations likely resulted from AMDEs. Tree lichens appear to incorporate particu- in caribou taken in late winter (February) than those taken in the fall. late and total gaseous Hg throughout the year, without being much af- Although no specifics on their diet were given, the authors attributed fected by Hg re-emission processes. The authors hypothesized that the this pattern to seasonal differences in diet. Unlike other northern ungu- uptake of Hg in lichen tissue and its interaction with lichenic acids pre- lates, the summer habitat of George River caribou rather than the winter vent it from further photoreduction and re-emission to the atmosphere. range appears to be particularly constraining for foraging (Messier et al., Lower concentrations of THg reported by Choy et al. (2010) for terrestri- 1988). Low fat reserves of females during the first month of lactation al lichens from another Arctic coastal area—presumably also affected by and in the fall, combined with low calf growth, suggest that caribou AMDEs—could be explained by the insulating effect of snow cover for are nutritionally stressed during summer (Crête and Huot, 1993; Huot, much of the year, as compared with tree lichens which are directly ex- 1989; Manseau, 1996). Therefore, it would be expected that these ani- posed to atmospheric Hg all year long. The proportion of THg as MeHg mals have lower kidney weights in the fall than in the spring along in caribou forage plants sampled in Yukon ranged from 0.5–31%, and with correspondingly higher THg concentrations in the fall. They also higher proportions were observed in most plant groups collected from may be including lichens in their summer diet if their preferred summer a coastal location on the North Slope as compared to an inland location forages are not available. (Gamberg, 2009), likely as a result of AMDEs. Fall-collected female Porcupine caribou had higher concentrations of renal THg than males. Females are physically smaller than males 7. Hg in terrestrial animals but have higher energetic demands due to reproduction and lactation. Therefore they eat more food (proportional to their body weight) and 7.1. Distribution of Hg in tissues and organs thus proportionally more Hg than males (Gamberg, 2009). This gender difference has also been demonstrated for Hg in mink where females Terrestrial wildlife in the Arctic typically have very low levels of have a significantly smaller body size than males (Gamberg et al., Hg, particularly when compared to marine wildlife. Caribou are an 2005b). exception because they often consume large amounts of lichen. In Although there has been no temporal trend in renal THg in the Por- general, kidney, liver and brain contain the highest levels of Hg cupine caribou herd over the last two decades, there has been discern- among body organs and tissues. Renal Hg concentrations in terrestrial ible annual variation (Fig. 6). The annual variation in THg levels in the animals are consistently higher than hepatic concentrations while the Porcupine caribou herd appears somewhat cyclic and is likely driven reverse is true for animals in both marine and freshwater environ- by environmental factors. Although concentrations of THg in male and ments (Fisk et al., 2003; Gamberg et al., 2005b; Kim et al., 1996). female caribou varied in a similar fashion, males lagged behind females

Barren-ground caribou 6

Woodland caribou 4 Moose

P 2 BF -1 dw) 0 C H BE A D K

T BT BV

MD Q

Fig. 5. Mean renal THg concentrations (±SD) (μgg-1 dw) in Arctic caribou and moose collected from 1999 to 2009. Abbreviations for the caribou herds are: A = Aishihik, BE = Bluenose East, BF = Baffin Island, BI = Banks Island, BT = Bathurst, BV = Beverly, C = Carcross, D = Dolphin and Union, GR = George River, H = Hart River, K = Klaza, P = Porcupine, Q = Qamanirjuaq, T = Tay. Abbreviations for the moose herds are: MD = Deh Cho, MY = Yukon. Data are from Gamberg et al. (2005a), Gamberg (2008, 2009, 2010), M Gamberg, unpublished data, Larter and Nagy (2000),andPollock et al. (2009). by about one year (Fig. 6). Female caribou may respond more quickly to deposition and its subsequent uptake in lichen (Gamberg, 2010). An as- environmental factors that control Hg bioaccumulation or may be more sociationwiththePacific Decadal Oscillation is suggested by a decrease sensitive to those particular drivers due to their smaller body size and in caribou Hg renal concentrations when the index is in a negative mode higher nutritional requirements. One hypothesis to explain, at least in and an increase when the index is in a positive mode. Further analysis is part, the cyclic inter-annual variation in THg levels of both male and fe- required to investigate this potential relationship and the underlying male caribou is the influence of the Pacific Decadal Oscillation—apat- processes. tern of climate variability over the Pacific Ocean—on atmospheric Hg 7.3. Hg in other terrestrial animals

Arctic hare (Lepus arcticus) and a variety of rodents sampled from the Canadian Arctic had notably low concentrations of THg (Choy et al., 2010; Gartner Lee, 2005; Pedersen and Lierhagen, 2006). One exception was a renal THg concentration of 2.94 μgg-1 dw in a composite sample of four red-backed voles (Myodes rutilus)fromYukon(Gartner Lee, 2005). This concentration is more similar to those in caribou than to other rodents. The cause for this relatively high value is unknown. Moose also had very low levels of THg, both in Yukon and the Northwest Territories (Fig. 6; Gamberg, 2010). Their diet consists primarily of willow, which is Hg-poor. Arctic fox had somewhat higher concentrations of hepatic THg (mean: 1.11 μgg-1 dw) than terrestrial herbivores (Hoekstra et al., 2003), perhaps due to their opportunistic scavenging of ﬁsh and/or marine mammals (Fuglei et al., 2007). In contrast, Choy et al. (2010) measured a low whole-body concentration (0.23 μg THg g-1 dw) in ermine (Mustela erminea), again likely related to their diet which consists almost exclusively of small rodents. Choy et al. (2010) found that snow buntings (Plectrophenax nivalis) also had low whole-body concentrations of THg (mean: 0.18 μgg-1 dw). Their accu- Fig. 6. Mean renal THg concentrations (+SD)(μgg-1 dw) in male and female Porcupine ﬂ caribou collected during fall between 1991 and 2009 (Gamberg, 2010). Sample sizes mulation of Hg was not in uenced by proximity to a seabird colony that ranged from 1-23 and averaged 10 animals/gender/year. has contaminated the local coastal area with Hg through the high-

Please cite this article as: Gamberg M, et al, Mercury in the Canadian Arctic Terrestrial Environment: An Update, Sci Total Environ (2014), http:// dx.doi.org/10.1016/j.scitotenv.2014.04.070 M. Gamberg et al. / Science of the Total Environment xxx (2014) xxx–xxx 11 density release of guano. Recently published data on willow ptarmigan microbial methylation and direct atmospheric MeHg deposition, but (Lagopus lagopus) collected in northern Canada from 1985 to 1994 re- further work is needed to confirm these hypotheses. vealed similarly low hepatic and renal THg concentrations (mean: Few published studies currently exist on Hg in Canadian Arctic soils. 0.07 and 0.23 μgg-1 dw, respectively) (Pedersen et al., 2006). Data from two High Arctic islands and the Beaufort Sea coast suggest there can be considerable regional variation in soil THg and MeHg con- 8. Knowledge gaps centrations. Limited investigations indicate that Arctic soils have the capacity to methylate Hg and to emit GEM to the atmosphere. However, Although significant advances have been made in understanding Hg the extent of this processing and implications for the local and regional dynamics within ice and snow, particularly relative to AMDEs, signifi- Hg cycles remain unknown. cant knowledge gaps remain in the biogeochemical cycling of terrestrial In general, terrestrial wildlife in the Canadian Arctic has low levels of Hg in the Arctic. Mechanisms of Hg reduction and estimates of emission THg, caribou having the highest concentrations among the species stud- from terrestrial substrates, as well as sites of Hg methylation remain ied. Recent research on Hg accumulation in Arctic vegetation indicates poorly characterized, particularly in soils. Atmospheric models of Hg de- that lichens contain more THg than other plant types such as shrubs, position exceed accumulation rates of Hg on Canadian Arctic glaciers by flowers, and willows. The importance of lichen in the diet of caribou at least one order of magnitude. Further work is required to validate may explain their higher THg burdens. Monitoring of THg levels in the model predictions against measurements of Hg deposition in the Porcupine caribou herd indicates no significant temporal trend over Canadian Arctic. Reasons for the sustained higher THg concentrations the last two decades, although there is discernible annual variation in Arctic glacier snow during the decade 1990-2000 are at present un- that is likely driven by yet-unidentified environmental factors. Seasonal clear, and further investigations of the relative importance of anthropo- variation and gender differences in caribou THg concentrations indicate genic versus natural sources (e.g., volcanic eruption) is warranted. Few the importance of bioenergetics and seasonal diet. Further investigation studies have been conducted on Hg in Arctic soils, but coastal erosion of of the pathways and processes of bioaccumulation is required to better permafrost has been found to be a significant source of Hg to the Arctic understand geographic and temporal trends of Hg in caribou. Some Arc- Ocean. Climate change may intensify this process, but further research is tic carnivores/scavengers feeding on marine mammal carcasses may necessary to fully understand the implications for the terrestrial ecosys- have elevated Hg levels and insects could potentially represent an im- tem. Additionally, Arctic soils may have the capacity to methylate Hg portant route of Hg exposure to some Arctic wildlife. Further research and to emit GEM to the atmosphere, and these processes may be influ- is required to determine whether these routes of exposure constitute enced by climate change. With respect to food webs, drivers of inter- asignificant concern. annual variation in Hg in Arctic caribou remain poorly understood. Ter- restrial food webs in Arctic coastal areas may receive input of Hg from marine sources, but this has not been explored. The role of insects and Acknowledgements insectivores in the trophic transfer of Hg also remains poorly resolved in Arctic terrestrial food webs. We would like to acknowledge the support of the Northern Contam- inants Program which funded much of this research. C. Zdanowicz and 9. Summary J. Zheng were also funded by Natural Resources Canada's Environmental Geoscience Program and through the International Polar Year initiative. In recent years, much new information has been collected on the Funding from Natural Science and Engineering Research Council of movement and fate of Hg in the terrestrial cryosphere. Terrestrial Canada (NSERC) and the Northern Contaminant Program support Hg snow at Arctic sites had THg concentrations that ranged three orders biogeochemistry research in the Poulain lab. Logistical support for Arctic fi of magnitude from b 1toN 100 ng L-1. The high variability in THg reflects eld work was provided by the Polar Continental Shelf Project. Snow atmospheric Hg deposition—mainly during AMDEs—and post- and ice sampling on Canadian Arctic glaciers was accomplished with depositional processes, including photoreduction and re-emission to the help of Dr. David Lean (Lean Environmental Consulting), staff the atmosphere, and burial and redistribution in the snowpack. Concen- from Auyuittuq National Park (Pangnirtung, NU), and students from trations of THg in snow, firn, and ice on Canadian Arctic glaciers are typ- Carleton University and the University of Ottawa (A. Smetny-Sowa, ically much lower (b1ngL-1) than those reported in snow surveys of V. Ter-Emmanuilyan, D. Bass). E. Yumvihoze, B. Wang, D. Bass, A. lowland terrestrial environments. The net deposition of THg to glaciers Smetny-Sowa, K. Fuller and B. Main also assisted with cold room and increases from north-to-south, likely due to latitudinal change in laboratory procedures. We would also like to thank the northern wet deposition and/or particulate scavenging. The contribution of hunters and trappers who provided wildlife samples for this research. photochemically-driven (AMDEs) Hg deposition to the annual burden Laboratory analyses of the wildlife samples were provided by Derek in glacial firn is thought to be small on Penny Ice Cap (67° N), but may Muir, Xiaowa Wang and Angela Milani. be proportionally greater, albeit still small, on ice caps of northern Ellesmere Island (≥81° N) where wet deposition plays a lesser role. References Net atmospheric deposition rates of THg inferred from glacier snow and ice are lower, by orders of magnitude, than accumulation rates in Barkay T, Poulain AJ. Mercury (micro) biogeochemistry in polar environments. FEMS sediments and peat, as well as flux estimates from atmospheric models. MicrobiolEcol2007;59:232–41. Barkay T, Kroer N, Poulain A. Some like it cold: microbial transformations of mercury in Multi-decadal trends in THg deposition reconstructed from Canadian polar regions. 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Please cite this article as: Gamberg M, et al, Mercury in the Canadian Arctic Terrestrial Environment: An Update, Sci Total Environ (2014), http:// dx.doi.org/10.1016/j.scitotenv.2014.04.070