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Science of the Total Environm

Hydrochemistry and mercury cycling in a High Arctic watershed

Raymond G. Semkina,T, Greg Mierleb, Roy J. Neureuthera

aNational Water Research Institute, Environment Canada, 867 Lakeshore Road, Burlington, ON, L7R 4A6, CanadabDorset Environmental Science Centre, Ontario Ministry of the Environment, P.O. Box 39, Dorset, ON, P0A 1E0, Canada

Abstract

Mass budgets for total mercury, major ions and nutrients were calculated for Amituk Lake, located on Cornwallis Island,

Nunavut, Canada. Total mercury in two distinct snowpacks averaged 1.25 and 4.21 ng L�1; the discharge-weighted

concentration of influent streams averaged 0.76 ng L�1. The recent and pre-industrial HgT fluxes in atmospheric deposition to

the catchment were estimated to be 0.57 and 0.23 Ag m�2 but through retention within the catchment and/or re-volatilization

from the melting snowpack, these decreased by 69% in the lake inflow. The spring freshet was the prime conduit for

transporting HgT into Amituk Lake. Because of limited mixing of surface runoff with the lake water column during snowmelt,

59% of the HgT input was directly discharged through the outflow, 16% entered the lake water column where concentrations

increased from 0.23 to 0.33 ng L�1 from June to August and 25% was deposited to the bottom sediments producing a sediment

HgT flux of 3.1 Ag m�2.

D 2005 Elsevier B.V. All rights reserved.

Keywords: Mercury; Arctic; Watershed; Spring melt; Lake mass budget

1. Introduction

1.1. Background

Elevated levels of persistent organic pollutants and

mercury in marine mammals and fish have been

reported from the Canadian Arctic since the early

1970s (Muir et al., 1999). Increased emissions and

deposition of these chemicals and their tendency to

persist in the Arctic environment and to bioaccumu-

late in aquatic food webs pose a health risk for top

0048-9697/$ - see front matter D 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.scitotenv.2004.12.047

T Corresponding author.

predators and northern aboriginal populations (Schin-

dler et al., 1995). The Canadian government estab-

lished the Arctic Environmental Strategy Northern

Contaminants Program in 1991 to focus research on

persistent organic pollutants, heavy metals, in partic-

ular Pb, Cd and Hg, and radionuclides. These

contaminants are often transported far from their

source areas into the Canadian Arctic via atmospheric

and/or oceanic currents. Numerous studies on the

sources, occurrence and pathways of these chemicals

and their biological effects in the marine, freshwater

and terrestrial environments of the Arctic and sub-

Arctic regions of Canada have been completed (Muir

et al., 1999; Macdonald et al., 2000). With respect to

ent 342 (2005) 199–221

60o

80o

Cornwallis Island

Amituk Lake and its watershed

CaveCreek

RockCreek

EastCreek

CampCreek

MudCreek

GorgeCreek

A

mituk aL ke

1000 m

Drainage Basins

N

Fig. 1. Location of Cornwallis Island and the Amituk Lake

Watershed.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221200

mercury, the paucity of reliable measurements in snow

and ice and in marine and freshwaters has been a

critical factor in deciphering the geochemical cycling

of this element. There is also a need to elucidate the

historical trends in deposition and receptor concen-

trations because Hg levels in the atmosphere are

reportedly increasing by 0.6 to 1.5% per year in the

Northern Hemisphere (Fitzgerald, 1995; Slemr and

Langer, 1992). Present-day Hg deposition is reputed

to be 3–5 times greater than in pre-industrial times and

human activities now contribute 50 to 75% of the total

yearly Hg input to the atmosphere from all sources

(Fitzgerald, 1995; Lindqvist et al., 1991).

A 1995 tabulation of worldwide mercury emissions

revealed that 1900 tonnes of anthropogenic mercury

were released to the atmosphere, 75% of which were

from the combustion of fossil fuels, most notably coal

(Pacyna and Pacyna, 2002). Asian countries contrib-

uted approximately 56% of global Hg emissions

followed by Europe and North America at less than

25%. Gaseous elemental mercury accounted for about

53% of total emissions, gaseous Hg2+ 37% and

particle-associated Hg 10%. That atmospheric mer-

cury, including Hg attributed to man-made sources,

was finding its way to remote areas in the world has

been supported by global biogeochemical models,

geographical trends in soil Hg and by the temporal

and spatial patterns observed for Hg concentrations

and fluxes in lake sediments and bogs (Fitzgerald et

al., 1998) and in glacial ice (Schuster et al., 2002).

At Alert in the Canadian High Arctic (82.58N,62.38W), measurements of atmospheric Hg were used

in a large-scale transport pathway model to suggest

source regions in eastern Europe, the northeast coast

of North America, the Northwest Territories in

Canada and in Siberia (Cheng and Schroeder, 2000).

Efforts to establish temporal trends in Hg deposition

to Arctic watersheds in Canada (Lockhart et al., 1998)

and elsewhere (Landers et al., 1998) have centered on

ratios of Hg concentration and/or Hg flux in dated

lake sediment cores. One of the objectives of this

study was to obtain similar information by calculating

a mass budget for mercury in Amituk Lake. With the

exception of earlier work at Char Lake (Schindler et

al., 1974), information on major ion, nutrient and trace

element cycling in a high Arctic watershed is limited

at best. This study would also be an opportunity to

expand the hydrological and chemical database for a

fragile resource that is now threatened by incursions

of complex chemicals and by a changing climate.

1.2. Study site

Amituk Lake is located at latitude 75802V57U andlongitude 93845V05U on the east coast of Cornwallis

Island in the Canadian Arctic Archipelago (Fig. 1).

The watershed is 50 km northeast of the hamlet of

Resolute, the sole settlement on Cornwallis Island and

the home to approximately 200 aboriginal and non-

indigenous inhabitants. The climate of Cornwallis

Island is classified as High Arctic (Ecoregions Work-

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 201

ing Group, 1989) with severely cold winters, short,

cool summers and very low annual precipitation. At

Resolute the long-term mean February air temperature

is �33 8C, the mean July air temperature is 4.1 8C,and the mean annual air temperature is �16.6 8C(Phillips, 1990). The mean annual frost-free period is

9 days (10–20 July). Annual precipitation averages

131.4 mm, of which 40% falls as rain from June to

September. Sunshine radiates the landscape for 24 h a

day from May to August but gradually decreases

towards the sunless winter months (November to

February).

The Amituk Lake watershed is 26.5 km2 in area

and contains six small basins, five of which drain

directly into the lake (Fig. 1). Gorge Creek has the

largest drainage area at 10.3 km2, followed by Mud

Creek (5.2 km2), Cave Creek (4.7 km2), Rock Creek

(1.1 km2) and Camp Creek (0.4 km2). The remaining

basin (2.0 km2) directs water into East Creek, which

flows into the lake outlet stream. The discharge from

Amituk Lake travels a distance of 5 km into Read Bay

and the Arctic Ocean. Morphometric surveys of

Amituk Lake indicated a surface area of 37.8 ha and

a mean and maximum depth of 19 m and 43 m

respectively (Semkin et al., 1993). Lake ice was 2.2 m

thick in early June prior to snowmelt.

Continuous permafrost underlies the Amituk Lake

watershed to a substantial depth (380–600 m at

Resolute as reported in Canada, Energy, Mines and

Resources, 1995). Thawing of the permafrost occurs

beneath the lake itself and in the catchment where the

thaw zone, or active layer, was measured down to

0.5–1.0 m in the late summer (Kinney, 1997).

Holocene glacial erosion and marine submergence

are the dominant geomorphological features of this

area (Edlund, 1991). Consolidated bedrock, often

mantled in a thin, discontinuous veneer of frost-

shattered rock, covers approximately 80% of the

watershed. A 1-m- to 2-m-thick layer of stony silty

loam till, predominant in the upper Mud Creek sub-

basin and in the northern end of Gorge Creek, covers

the other 20% (Kinney, 1997). In terms of composi-

tion, the bedrock consists primarily of limestone,

dolomite and calcareous shales of late-to-mid-Paleo-

zoic age (Thorsteinsson et al., 1986); the till is locally

derived and consequently highly alkaline. Distinct

topographical features include 80- to 100-m-high

slopes along the east–west axis of the lake, a broad

upland plateau which is the source area of the

tributary streams, and a major escarpment rising 120

m above the west end of Amituk Lake and separating

the lake drainage basin from that of its major inflow,

Gorge Creek. Fluvial deposits at the mouth of the

streams form rock–rubble deltas extending out into

the lake—features which attest to the force of the

spring runoff.

The abundance and diversity of vegetation, partic-

ularly vascular plants, are limited in the Amituk Lake

watershed because of the dry, cold climate but also as

a result of the thin and patchy development of soil on

a very alkaline substrate (Edlund, 1991). In areas

moistened by snowmelt, pockets of saxifrage, arctic

poppy, dwarf willow, dryas and sedge were observed.

Several varieties of lichen were also noted on the

bedrock and boulders throughout the catchment as

were aquatic mosses in the streams and small rivulets

emanating from the melting snowpack.

bThe Canadian Arctic Archipelago represents a

large polar ecozone where vegetation, bedrock and

climate can have significant impacts on chemical

structure and biological productivity of freshwatersQ(Hamilton et al., 2001). Amituk Lake, like most Arctic

freshwater systems, is considered ultra-oligotrophic

with low nutrient concentrations, low algal biomass

and low productivity. Phytoplankton surveys in the

spring and summer of 1993/94 revealed chlorophyll

levels ranging from 0.18 to 1.20 Agd L�1 and counts

of mainly unicellular algae ranging from 18 to

48�106 cellsd L�1 (Semkin et al., 1996). Chrysophy-

ceae was the most dominant algal group in terms of

number of cells (N90%) and biomass (N70%) followed

by Cryptophyceae and Chlorophyceae in 1993 and

Cyanophyceae in 1994. In terms of zooplankton, net

(150 Am mesh size) hauls through the water column in

the spring and summer of 1994 collected only

calanoid copepods (B. Koenig, personal communica-

tion). Low species diversity and biomass were also

noted for the lake benthos which were essentially

Chironomidae with the exception of the occasional

oligochaete (M. Fox, personal communication). Chi-

ronomidae was also the most abundant benthos in

neighbouring Char Lake (Welsh, 1975) where it was

the main food source for Arctic char (Salvelinus

alpinus), the only fish species observed in both lakes

(D. Muir, personal communication). Elevated Hg

levels in muscle (0.57F0.60 Ag g�1 fresh weight)

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221202

and in liver (1.24F1.55 Ag g�1 fresh weight) were

measured in char at Amituk Lake (Muir and Lockhart,

1992) and were attributed to Hg biomagnification

supported in part by the long life span and low growth

rate of these fish in cold Arctic waters (Schindler et

al., 1995).

2. Materials and methods

2.1. Hydrometric measurements

The snowpack in the Amituk Lake catchment was

surveyed from 03–11 June 1994 prior to the produc-

tion of snowmelt in the stream channels. Snow depth

and snow water equivalent (SWE) were measured in

the field with a standard snow scale. Samples from the

deeper snowpack were collected with a 1.5-m Teflon-

lined box corer or a CRELL corer and were weighed

on a digital scale at the base camp. SWE values were

calculated from the sample weight and the diameter of

the corer. Results from the snow surveys were

discretized onto 200-m by 200-m grids overlain on

photographic images of the watershed (methodology

outlined in Woo and Rowsell, 1993). Using the grid

counts, a mean SWE for the overall watershed was

estimated. Precipitation falling during the study period

was quantified in a standard rain gauge located near

the lake outflow.

Prior to snowmelt, a 50-gallon polyethylene barrel

was perforated in its lower half and anchored to the

frozen ground in each of the 6 stream channels.

Stevens chart recorders were then mounted on the

barrels to provide a continuous record of the stream

stage. Instantaneous discharge measurements were

made at least daily during high flows and less

frequently during the reduced summer flow period.

Using stage-rating curves and the continuous level

record, daily values of stream discharge were

calculated.

Piezometers were used to measure the level and

chemistry of subsurface waters in the active thaw

zone. These consisted of 1-m-long, high-density

polyurethane tubing (0.25 in. I.D.) with the bottom

10 cm perforated and wrapped in Nitex mesh (Kinney,

1997). The piezometers were emplaced at 10 sites in

the catchment—5 in the streambeds and 5 in the

littoral zone at depths b0.5 m.

2.2. Sampling

The shallow snowpack on the lake ice and on the

upland plateau was sampled for major ion and nutrient

analysis using an aluminum or Plexiglas corer

(diameter=14 cm). The deep valley snowpack was

sampled by excavating a snow pit to ground level or

by using the Teflon-lined CRELL corer (diameter=7.6

cm). The snow samples were then transferred to clean

polyethylene bags and melted in the field laboratory.

Snowpack samples for HgT analysis were collected

with the Teflon-lined box corer or the CRELL corer,

depending upon snow depth. Samples for HgT were

transferred to clean Teflon-lined stock pots with lids

and melted in the field laboratory.

Grab samples for major ion, nutrient and trace

element analysis were collected at the six stream sites

on a schedule reflecting the hydrological conditions—

daily during the spring freshet and every 1–2 days

thereafter until the end of the field season. Stream

samples for the determination of HgT were collected

every 1–2 days during the high spring flows and at

least weekly during low flows.

A total of 11 weekly sampling surveys were carried

out on Amituk Lake from 15 June to 22 August. All

samples were collected at the deepest point in the lake

(43 m) using a peristaltic pump. Samples were taken

for major ions and nutrients at 1-m intervals beneath

the ice to a depth of 10 m, and at 15-, 20-, 25-, 30-,

35-, 40- and 41-m depths. Additional samples were

collected for total phosphorous (TP), total nitrogen

(TN) and particulate organic carbon (POC) at depths

of 3, 20 and 40 m. Profiles of water temperature and

specific conductance were also conducted during the

sampling surveys. Amituk Lake was sampled for HgTat 1-m intervals (0–5 m) and at 10, 20, 30 and 40 m

four times over the study period.

Samples of groundwater were extracted from the

piezometers in mid-August using a peristaltic pump

and were submitted for major ion and nutrient

analysis.

Rock samples were collected from the consolidated

bedrock in the stream valleys using a geological

hammer and were submitted to a geochemical

laboratory for trace element analysis, including

mercury. Fresh, unweathered samples were selected

to improve the accuracy and precision of the

analytical measurement.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 203

In June 1993, Amituk Lake sediments were

sampled at three sites from the lake ice using a

Technical Operations light-weight gravity corer with a

4-in. Plexiglas core barrel. The sediment cores were

subdivided at the field laboratory into 1-cm intervals

and submitted to the Freshwater Institute, Fisheries

and Oceans Canada, in Winnipeg for mercury

analysis.

2.3. Chemistry

A 10 ft by 25 ft clear polypropylene tent was de-

dicated as a field laboratory in the base camp located

several hundred meters downstream from the lake

outlet. A gasoline generator provided power for basic

filtration apparati and for a constant-temperature

circulating bath and organic extractor used in a parallel

study of persistent organic pollutants (POPS) in

Amituk Lake (Helm et al., 2002). Water and snowpack

samples were analyzed for pH and specific conduc-

tance and processed for other tests in the field

laboratory immediately after collection. Sub-samples

for major ions (Ca2+, Mg2+, Na+, K+, SO42�, Cl�),

alkalinity and nutrients (NO3�, NH4

+, dissolved organic

carbon or DOC, SiO2) were transferred to 250-mL

polyethylene bottles and stored in a cool place until

delivery to the main laboratory in southern Ontario.

Alkalinity was measured by Gran titration; the alkaline

and alkali cations by atomic absorption and flame

photometry respectively; the anions and nutrients were

measured colorimetrically on a Technicon auto-analy-

ser following standard methods prescribed by Environ-

ment Canada (Department of the Environment, 1979).

Sub-samples for the measurement of TN/TP were

collected in 125-mL bottles and preserved with 30%

H2SO4. Samples for TP and TN were subjected to the

molybdophosphoric blue and automated cadmium

reduction methods prior to colorimetric analysis on a

Technicon auto-analyser. Total acid-extractable trace

elements were collected in 125-mL bottles and

preserved with ultrapure HNO3 for subsequent anal-

ysis by inductively couple plasma (ICP) and graphite

furnace atomic absorption. Selected water samples

were filtered through pre-treated (450 8C for 1 h)

Whatman GF/C filters which were kept cold prior to

POC measurement on a CHN analyzer.

A high level of diligence was exercised during

sample collection and processing to ensure the

integrity of the HgT samples prior to analysis. All

water and snowmelt samples were collected in 250-

mL Teflon bottles with solid Teflon caps using a

peristaltic pump equipped with C-flex tubing for the

pump head and Teflon tubing. The bottles and tubing

were cleaned in caustic ethanol (1M KOH plus

ethanol, 1:1) to remove any organic films and rinsed

thoroughly. To remove mercury the bottles and tubing

were filled with 10% hydrochloric acid, autoclaved

for 15 min at 120 8C and thoroughly rinsed. Finally

the bottles and tubing were soaked for at least 24 h in

a mixture of 20% nitric acid, 2% hydrochloric acid

and 0.05% potassium dichromate, and then rinsed

with Hg-free water. Bottles and Teflon tubing were

double bagged in Ziploc bags during transport. In the

field, clean latex gloves were used during sampling.

After rinsing with sample at least 3 times, the Teflon

bottles were filled to capacity and the sample injected

with 0.5 mL of Hg-free 50% hydrochloric acid for

preservation. The bottles were tightly capped and re-

bagged for shipment to the laboratory. Approximately

10% of the samples were collected in duplicate to

assess overall precision. Four travel blanks (bottles

filled in the laboratory, shipped to the collection site

and spiked with preservative in the field) were also

collected to assess contamination.

Total mercury in unfiltered snowpack and water

samples was measured in a clean laboratory dedicated

to the ultra trace analysis of mercury at the Dorset

Environmental Science Centre of the Ontario Ministry

of the Environment. Samples were analyzed with a

technique similar to that proposed by Gill and Bruland

(1990). Approximately 40-mL portions of sample

were transferred to Teflon tubes and spiked with 1 mL

of 1% hydrogen peroxide. Using an automated

system, samples were pumped into a sparger along

with approximately 5 mL of 0.0125% (w/v) sodium

borohydride in 2 N NaOH to reduce Hg. Samples

were flushed with Hg-free argon at 400 mLdmin�1

and the entrained Hg vapour was trapped on gold-

coated sand. After the solution was stripped, the Hg

was thermally desorbed and flushed into a Brooks

Rand atomic fluorescence detector. Most samples

were analyzed with and without a spike addition to

assess recovery. All analytical runs also included

determination of contamination from the system and

reagents, and appropriate corrections were applied to

sample analyses. Based on the variability of purge

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221204

blanks the instrumental detection limit (3 times the

standard deviation) was about 3 pg. For a 40-mL

sample portion, this yielded an instrumental detection

limit of about 0.08 ng L�1. Based on the variability of

the zero standard, the working detection limit was

0.15 ng L�1. Based on 16 analytical runs the median

within-run coefficient of variation of the 1.25 ng L�1

standard was 6%.

Rock samples for mercury analysis were crushed

and pulverized to b150 mesh and digested for 2 h in a

hot mixture of concentrated NHO3:HCl (1:3). Follow-

ing the addition of SnCl2, mercury in solution was

reduced to Hg0 which was then measured by cold

vapour atomic absorption spectrophotometry (EPA,

1981). The detection level was 5 Ag g�1. Sub-samples

(0.1–0.5 g) of freeze-dried lake sediment were heated

to a gentle boil with 8 mL of aqua regia and adjusted

to 50 mL with distilled water. The supernatant was

analyzed for mercury by cold vapour atomic absorp-

tion spectrophotometry (Lockhart et al., 1995).

Reference sediments from the National Research

Council of Canada were co-analyzed for quality

assurance.

2.4. Mass budget calculations

The calibration of Amituk Lake considered

various water and chemical inputs and outputs.

The snowpack chemical burden was a blend of deep

valley snow and shallow snow on lake ice and the

upland plateaux and was calculated by multiplying

the SWE value in each of the snowpacks by their

respective chemistries and summing the results. The

chemical burden in summer precipitation was

estimated by multiplying the total precipitation

quantity recorded at Amituk Lake (June–August)

by the chemical composition of the late winter,

valley snowpack. Chemical loadings in the snow-

pack and in summer precipitation were then

combined to estimate the chemical burden in

atmospheric deposition. The gauged stream input

was calculated by combining daily stream chemistry

(measured or interpolated) with daily discharge as

described by Jeffries et al. (1988). Estimates were

also made of the mass loading to Amituk Lake

attributed to surface runoff from the ungauged

slopes and to groundwater inflow. The ungauged

lake input, primarily from the slopes surrounding

the lake, was determined by multiplying the gauged

stream input by 0.1 which was the ratio: (ungauged

drainage area)/(gauged drainage area). The quantity

of ground water entering Amituk Lake (QGW) was

estimated using a chloride mass budget: QSW

Cl�SW+QPCl�P +QGWCl�GW=QOFCl

�OF+D(QLakeCl

�Lake)

where SW was surface water, P precipitation, GW

ground water, OF was the lake outflow and D(QLake

Cl�Lake) the change in the Cl� content of lake water. If

one assumes steady-state conditions for Cl� such that

the DCl�Lake=0, then by measuring the quantity of

surface water, precipitation and lake outflow along

with the Cl� concentrations in the four media, it was

possible to estimate QGW. The ground water mass

input was then calculated by multiplying the ground

water inflow by the average chemistries of the ground

water samples. The ground water HgT input was the

exception in that the ground water HgT concentration

was estimated from the late summer HgT stream

concentration. Other components of the lake input

included the snowpack overlying the lake surface ice

and the spring/summer precipitation falling directly

on the lake surface. The former was calculated by

multiplying the mean SWE of the snowpack on the

ice surface by both the lake area and the mean

chemical content of the snowpack. The total lake

input was tallied by summing the contributions of

water and chemicals from the five media—gauged

and ungauged surface runoff, ground water, snow-

pack and precipitation on the lake surface. Chemicals

introduced into Amituk Lake from the catchment and

the atmosphere followed at least one of three path-

ways—direct export out of the lake via the stream

outflow, incorporation into the lake ‘water column or

sedimentation to the lake bottom. The gauged lake

output was calculated by the same method as used for

the gauged stream input. The increase (or decrease) in

the chemical burden of the lake water column was

essentially the change in the lake chemical content

from June 15 to August 22 plus the chemical burden

associated with bnewQ water added to the lake from

the spring freshet and melting of ice on the lake

surface. The chemical content of Amituk Lake for a

given date was calculated by summing the chemical

burdens from discrete 5-m depth intervals (e.g., lake

volume 0–5 m�average water chemistry 0–5 m)

down through the lake water column. The chemical

burden associated with bnewQ water was calculated by

Table 1

Snow water equivalent (SWE) compared to snowfall at Resolute

Year SWE at Amituk

Lake (mm)

Precip at Resolute

September–June (mm)

Dates of precipa

accumulation

1994 133.8 99.0 06 Sep–03 Jun

1993 116.5 100.8 11 Sep–13 Jun

1992 112.5 98.2 10 Sep–19 Jun

a Assumed precipitation as snow in September when maximum

air temperature b08C and as rain in June when maximum air

temperature N08C.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 205

multiplying the average chemistry of the lake water

column on August 22 times the difference between

the sum of the water inputs and the lake outflow. And

finally, the quantity of material deposited to the lake

sediments was simply the difference between the sum

of all lake inputs and the lake output plus change in

chemical content of the lake water column.

In addition to defining recent HgT fluxes to Amituk

Lake and to the lake bottom sediments, the mass

calibration exercise allowed for an estimation of

historic (i.e., pre-industrial) HgT fluxes. Based upon

the assumptions that rates of geochemical weathering

in the watershed and the physico-chemical dynamics

regulating HgT partitioning in Amituk Lake, partic-

ularly with respect to sediment sequestration, and HgTretention within the catchment have not changed since

historic times, historic HgT fluxes were estimated

from the following relationships.

(i) Historic sediment HgT flux:

HgTð ÞRECENT SED FLUX = HgTð ÞHIST SED FLUX

¼ Hg½ �RECENT= Hg½ �HISTwhere the square brackets denote sediment Hg

concentrations at the surface (recent) and at depth

(historic).

(ii) Historic lake input HgT flux:

HgTð ÞRECENT LAKE FLUX = HgTð ÞRECENT SED FLUX

¼ HgTð ÞHIST LAKE FLUX = HgTð ÞHIST SED FLUX

(iii) Historic atmospheric deposition HgT flux:

HgTð ÞRECENT ATM FLUX = HgTð ÞRECENT LAKE FLUX

¼ HgTð ÞHIST ATM FLUX = HgTð ÞHIST LAKE FLUX

3. Results

3.1. Quality assessment of HgT measurements

The mean Hg level (0.19 ng L�1, range 0.15 to

0.22) in the four travel blanks was marginally above

detection, but it was not significantly different than

the initial level of Hg in the blank water. Overall

recovery of spike additions averaged 96.2% (F14.6%,

n=216) and was not significantly different between

snowpack samples and stream and lake samples. The

median difference in 12 pairs of field duplicates was

0.13 ng L�1; 8 of the pairs differed by b0.2 ng L�1.

The first two pairs of snow samples exhibited

relatively large differences (0.8 and 2.0 ng L�1), a

possible indication of contamination, perhaps from the

container used in melting the snow. However, the

average concentration of the pairs was similar to that

in subsequent samples, and the average value was

accepted.

3.2. Atmospheric deposition

Snowpack surveys in 1994 involved the collection

of 49 composite cores on the upland plateaux and on

the lake ice and at least one composite core from

each of the six stream valleys. Measurements of

snow depth and SWE in the shallow snow averaged

0.47 m and 204 mm, respectively; the deeper valley

snowpack recorded an average depth of 2.76 m and

average SWE of 1803 mm. The SWE in the overall

catchment was estimated to be 133.8 mm of which

38% was derived from the deep valley snowpack,

although this sector constituted only 8% of the basin

surface area. The SWE values calculated for the

1994 snowpack data and from earlier snow surveys

(R. Semkin, unpublished data) were comparable to

the quantity of precipitation measured at Resolute for

what may be considered the period of snow

accumulation, September–June (Table 1). The small

but consistently higher SWE values may have

reflected field or computational errors or the ten-

dency of the standard snow gauge at Resolute to

have under-collected snowfall during the extremely

high wind conditions that are common to Arctic

winters (Woo, 1998).

Table 2

Snowpack and water chemistrya in the Amituk Lake watershed

Shallow snowpackb Valley snowpackc GWd Stream inflowe Amituk Lakef Lake outflowe

pH 7.11 6.47 8.29 8.07 8.32 8.15

pH range 6.41–9.04 6.19–7.12 7.95–8.56

Sp.Cond. 21.5F12.4 18.3F12.5 216F127 103 138 116

Ca2+ 2.57F2.14 0.87F0.50 29.7F12.2 15.7 20.6 17.8

Mg2+ 0.54F0.36 0.55F0.42 8.47F7.81 3.08 4.20 3.34

Na+ 0.73F0.57 1.23F0.89 2.12F1.48 1.01 1.48 1.23

K+ 0.08F0.08 0.19F0.10 0.28F0.15 0.15 0.17 0.18

NH4+–N 0.008F0.007 0.031F0.024 0.004F0.007 0.007 0.002 0.005

Alkalinity 0.137F0.101 0.031F0.024 1.798F0.558 0.986 1.320 1.105

SO42� 0.56F0.27 0.87F0.11 10.2F14.9 1.26 2.09 1.38

NO3�–N 0.029F0.012 0.041F0.003 0.133F0.119 0.031 0.015 0.022

Cl� 1.68F1.60 3.34F2.51 4.32F2.06 2.29 3.15 2.77

SiO2 0.17F0.18 0.09F0.03 0.90F0.81 0.32 0.27 0.41

DOC 0.85F0.67 0.43F0.30 0.66F0.18 0.67 0.63 0.66

POC 0.62F0.59 0.44F0.33 0.13F0.16 0.10 0.04 0.08

Total P 0.0043F0.0031 0.0044F0.0030 0.0092F0.0142 0.0210

Total N 0.136F0.077 0.184F0.194 0.243F0.184 0.078

HgT 1.25F0.46 4.21F2.29 n.a. 0.76 0.23–0.33 0.52

a Concentrations as mg L�1 except specific conductance (AS cm�1), alkalinity (meq L�1) and HgT (ng L�1).b Pre-melt shallow snowpack: meanFs.d. from 47 samples except for HgT (16 samples).c Pre-melt valley snowpack: meanFs.d. from the 6 stream valleys (n=6).d Groundwater average of 12 samples from 10 piezometers in stream beds and littoral zone in Amituk Lake.e Stream and lake outflow concentrations are discharge-weighted for the period of study.f Chemistry from whole-lake, volume-weighted sample collected 22 August.

Table 3

Total mercury levels (ng L�1) in remote areas

Site Snowpack Surface

water

Reference

Amituk Lake 1.25–4.21 0.23–0.76 This study

Arctic Canada 2.2–34 Lu et al., 2001

Arctic Alaska 1.5–7.5 Snyder-Conn

et al., 1997

Cli Lk, Canada 2.53–3.95 0.24–0.36 Evans and

Lockhart, 1998

Arctic Russia 0.30–1.00 Coquery et al., 1995

Lakes in Sweden 1.35–15 Lee and

Iverfeldt, 1991

Lakes in Finland 1.3–7.2 Verta et al., 1994

Lake Baikal, Russia 0.14–0.77 Meuleman

et al., 1995

ELA, Ontario 1.50F0.81 Kelly et al., 1995

Harp Lake, Ontario 1.6–3.2 Mierle, 1990

Lake Superior 0.49F0.22 Hurley et al., 2002

Glacial Nat Pk USA 0.35–2.85 Watras et al., 1995

High-altitude

lakes, USA

1.07F1.41 Krabbenhoft

et al., 2002

Northern Minnesota 0.2–3.2 Monson and

Brezonik, 1998

Wisconsin Lakes 0.7–2.1 Watras et al., 1994

Adirondack Lakes 0.8–5.3 Driscoll et al., 1994

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221206

Apart from dissimilar physical attributes, the

chemical composition of the shallow snowpack was

different from that of the deeper valley snowpack

(Table 2). The shallow snowpack was more alkaline

with a higher pH (7.11 versus 6.47) and Ca2+ content

(2.57 versus 0.87 mg L�1) whereas the valley

snowpack recorded higher concentrations of Na+

(1.23 versus 0.73 mg L�1), Cl� (3.34 versus 1.68

mg L�1) and SO42� (0.87 versus 0.56 mg L�1). Total

mercury also varied in the two snowpacks—from 1.25

ng L�1 in the shallow to 4.21 ng L�1 in the valley

snowpack, concentrations that were comparable to

values reported elsewhere in the Canadian north and

in Alaska (Table 3).

In addition to water generated by the melting

snowpack, 57.8 mm of precipitation fell on the

Amituk Lake watershed from June to August, of

which approximately 20% was snow. Of the 35

precipitation events recorded during this time, 90%

were less than 5 mm, with the heaviest precipitation

occurring in the latter part of the summer.

In terms of total water available to the catchment

from atmospheric deposition, 69% was attributed to

Table 4

Atmospheric deposition in the Amituk Lake watershed

Snowpack Precipitation Sum

H2O�10�6 m3 3.543 1.556 5.099

H+ Eq 635 531 1166

Ca2+ kg 6794 1354 8148

Mg2+ kg 1927 856 2783

Na+ kg 3267 1914 5181

K+ kg 433 296 729

Alk kEq 342 48 390

SO42� kg 2406 1354 3760

Cl� kg 8211 5196 13407

SiO2 kg 490 134 624

NH4+–N kg 60 48 108

NO3�–N kg 119 64 183

DIC kg 4690 912 5602

DOC kg 2451 674 3125

POC kg 1939 680 2619

TP kg 15 7 22

TN kg 547 286 833

Hg total mg 8455 6612 15067

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 207

the shallow and valley snowpacks and 31% to

summer precipitation (Table 4). On an equivalents

basis, the cation composition of atmospheric depo-

sition consisted of Ca2+ (46%), Mg2+ and Na+ (26%

and 25% respectively), K+ (2%) and NH4+ (1%).

With respect to anions, alkalinity and Cl� each

contributed about 45% of the anion content whereas

SO42� and NO3

� added 9% and 2% respectively.

Total mercury in atmospheric deposition was esti-

mated to be 15,067 mg of which 56% resided in the

1

5

4

3

2

6

Julian

Dis

char

ge (

m3

s-1

)

a)

0

60

40

20

1

Cum

Q

0160 180 20

Fig. 2. Hydrographs of daily (a) and cumulat

snowpack and 44% was associated with summer

precipitation. This quantity translated into a HgTconcentration of 2.96 ng L�1 and an annual HgT flux

of 0.57 Ag m�2d year�1 (Table 7).

3.3. Streams

Because of the southern exposure, snowmelt was

first observed in the still-frozen streambeds of Mud

and Camp Creek on 12 June (Day 163). By 16 June,

water was moving in East Creek. Snow dams in the

deeply incised stream valleys delayed the flow of

water for several more days in Gorge and Rock

Creeks and, in Cave Creek, surface runoff did not

appear until 26 June at which time a snow dam was

breached and a flood of meltwater deepened the

stream channel and transported sand and gravel some

tens of meters out onto the lake ice. Elevated flow

conditions from the influx of snowmelt lasted for just

over 3 weeks with the total daily stream inflow

peaking at ~5.3 m3 s�1 on 30 June (Fig. 2). Gorge

Creek, with the largest drainage area contributing to

Amituk Lake (40%), provided 56% of the total stream

input. Water discharging from the lake itself was first

measured on 17 June and produced a hydrograph

similar to that generated by the cumulative stream

inflow, albeit with a 1- to 2-day lag time.

Stream water chemistry in the Amituk Lake basin

was alkaline in nature with pHN8.0 and Ca2+ and

alkalinity concentrations (discharge-weighted) of 15.7

Day

Stream Inflow

Lake Outflow

60 180 200 240220

b)

0 240220

ive (b) stream inflow and lake outflow.

Hg T

(ng

L-1)

Stre

am Q

(m

3 s-1

)

Julian Day

(n=97)2

1.6

1.2

0.8

0.4

0

160 170 180 190 200 210 230220 240

6

5

4

3

2

1

0

Fig. 3. Concentrations of HgT in the six streams flowing into Amituk Lake.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221208

mg L�1 and 0.986 meqd L�1 respectively (Table 2).

Concentrations of organic carbon and nutrients were

close to the levels of analytical detection. In terms of

HgT, the discharge-weighted concentration averaged

0.76 ng L�1 for the 6 streams decreasing to 0.52 ng

L�1 in the lake outflow. Concentrations of HgT in

surface waters at the study site were generally at the

low end of the range reported for remote sites in the

Northern Hemisphere (Table 3).

Concentrations of HgT in stream water were

elevated (1.4 ng L�1) at the beginning of snowmelt,

decreased through the spring freshet and stabilized

during the low summer flows to around 0.4 ng L�1

(Fig. 3). This pattern is clearly displayed in Rock

Hg (ng L-1)

DOC (mg L-1)

Julian D

Con

cent

ratio

n

170 1800.4

1.6

1.2

0.8

Fig. 4. Concentrations of HgT and DOC in

Creek where a high initial concentration of HgT at the

start of stream flow was accompanied by elevated

levels of DOC (Fig. 4). Secondary spikes in HgTconcentration in the influent streams also occurred

both during the spring at high flow conditions and

during the summer when the discharges were lower.

These peaks were frequently related to high levels of

suspended solids, POC, and trace elements (Fe, Al,

Pb). Major ions and soluble nutrients also displayed

elevated concentrations at the initiation of stream

flow. During the spring freshet, relatively high

concentrations were maintained for H+ and NH4+

whereas most chemicals showed a reduction in

concentration from dilution effects at the higher

Q

ay190

Dis

char

ge (

m3 s

-1)

0.1

0.3

0.2

0.0

Rock Creek during the spring freshet.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 209

flows. In the post-freshet period, stream concentra-

tions steadily increased for Ca2+, Mg2+, alkalinity,

SO42�, and NO3

� but remained relatively constant or

decreased for H+, Na+, K+, NH4+, Cl� and DOC. The

dichotomy in the behaviour of these two chemical

groups is illustrated by temporal changes in the

concentration of Ca2+ and NO3� compared to that of

Cl� (Fig. 5).

3.4. Groundwater

The Cl� mass budget for Amituk Lake estimated

that 0.331�106 m3, or about 5% of the total water

input to the lake, was from groundwater. The

composition of groundwater in the catchment was

dominated by alkaline cations and by alkalinity.

Relatively longer residence times of ground water in

the active layer resulted in concentrations that were

essentially double those recorded for the influent

streams (Table 2). Nitrate and SO42� were even more

concentrated (4–8 times) in groundwater than in the

stream water, whereas DOC and NH4+ recorded

comparable or reduced levels in groundwater. On an

equivalents basis, Ca2+ and Mg2+ constituted 51% and

45% respectively of the cations in groundwater but

84% and 14% of the stream water cations. Sulphate

comprised about 10% of the anion content of ground-

Con

cen

(mg

L-1)

160 180 200

Julian

25

20

15

10

5

0

Q

C

Cl (x

Fig. 5. Chemographs of Ca2+, Cl�

water compared to 2% in surface water. Alkalinity

formed 84% of anions in groundwater but 91% in

stream waters. Total mercury was not measured in

groundwater.

3.5. Amituk Lake

The mixing of alkaline surface and groundwaters

in Amituk Lake resulted in an average lake water

composition characterized by a high pH (8.3) and

Ca2+ and alkalinity concentrations of 20.6 mg L�1 and

1.32 meqd L�1 (Table 2). Comparing the lake chem-

istry to that of the inflowing streams and the outflow,

several observations were pertinent: (i) the pH,

specific conductance and concentration of most major

ions were higher in Amituk Lake than in both the

streams and outflow; (ii) nutrient levels (NH4+, NO3

�

and SiO2) in Amituk Lake were less than concen-

trations in the streams and outflow; (iii) the whole-

lake, average concentration of HgT was lower than the

time-integrated (discharge-weighted) stream and out-

flow concentrations.

As cold (~0 8C) and relatively dilute snowmelt

entered Amituk Lake during the spring freshet, a layer

of bnewQ water formed beneath the ice cover. The

meltwater lens, as delineated by isopleths of temper-

ature (Fig. 6a) and specific conductance (Fig. 6b), was

Dis

char

ge (

m3 s

-1)

220 240

Day

4

3

2

1

0

a

3)

NO3 (x100)

and NO3� in Gorge Creek.

0.25

0.25

0.30

0.30

0.350.4

00.45

0.500.5

50.60

0.30

0.20

0.25

0

-10

-20

-30

-40170 180 190

Julian Day

c) Total Mercury (ng•L-1)

200 210 220 230

ICE

0

-10

-20

-30

-40

0

-10

-20

-30

-40

170

170

180

180

190

190

Lake

Dep

th (

m)

Lake

Dep

th (

m)

Lake

Dep

th (

m)

200

200

210

210

220

220

230

2304.

24.

2

4.0

4.0

3.8

3.8

3.6

3.6

3.4

3.4

3.2

3.2

3.0

3.0

2.8

150

110120130140

140

150

160

2.6

2.4

ICE

ICE

b) Specific Conductance (µS•cm-1)

a) Temperature (oC)

2.2

2.6

2.8

2.8

2.6

3.02.

8

2.42.01.8

Fig. 6. Isopleths of temperature (a), specific conductance (b) and

HgT (c) in Amituk Lake.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221210

observed to deepen with increasing stream flow. The

congruence of the isopleths of HgT (Fig. 6c) and

temperature/specific conductance suggested that

snowmelt was also the main conduit for the delivery

of HgT to Amituk Lake during this time. By Day 180

(29 June), HgT levels had increased to greater than

0.60 ng L�1 just beneath the 1.8-m-thick ice cover. In

terms of the lake water column, the influx of HgT

resulted in a 43% increase in concentration from a pre-

melt level of 0.23 ng L�1 to 0.33 ng L�1 by 7 August.

3.6. Lake sediments

Three sediment cores were collected in the western

leg of Amituk Lake at water depths of 14, 26 and 41 m

(Fig. 7). Core lengths were 39 cm (C1), 29 cm (C2)

and 30 cm (C3). Core C3, collected at the deepest

point, was composed of dark brown material contain-

ing layers of light grey and/or light brown sediment

with the laminations more pronounced in the upper-

most 20 cm. The other two cores had less stratigraphic

detail and consisted of light brown surface material

approximately 2-cm-thick overlying grey sediment.

Total Hg concentration in the top 1 cm of sediment

averaged 45 ng g�1 (60 ng g�1 in core C3; 38 ng g�1 in

core C1 and 37 ng g�1 in core C2). The Hg concen-

trations in all 3 cores leveled off to a relatively constant

value of 18 ng g�1 at a sediment depth of about 8 cm.

3.7. Rock chemistry

A total of thirteen fresh, unweathered rock samples

were collected from 5 of the 6 stream valleys in the

watershed (East Creek basin was not sampled).

Samples were purposefully selected to avoid any

visual traces of sulphide mineralization which was

noted in the bedrock as pyritic nodules oxidized to a

yellow-orange stain. Additional samples containing

these same nodules were taken to characterize the

chemical content of the sulphide mineral assemblage.

The mercury content of the 13 samples ranged from 8

to 18 ng g�1 and averaged 12.1F3.5 ng g�1, con-

centrations which were consistent with Hg values from

other calcareous sedimentary rocks (Table 5). Analysis

of two pyritic nodules separated from the host rocks

indicated elevated levels of Fe, Zn, Pb, Cu and Ni as

well as high concentrations of Hg (2050 and 6970 ng

g�1). Two samples of the rock matrix containing the

pyritic nodules also showed metal enrichment and Hg

concentrations of 44 and 64 ng g�1.

3.8. Water and chemical budgets—Amituk Lake

The water budget for Amituk Lake revealed that

93% of the total water input was from surface runoff,

5% from ground water and 2% from direct precip-

Sediment Depth (cm)

60

50

40

30

20

10

0

Hg

(ng•

g-1)

0 5 10 15 20 25 30 35

Core 1 Core 2 Core 3

Sediment Cores110

10

20

20

30 30

40 4043

2

3N

Fig. 7. Concentrations of HgT in 3 lake sediment profiles from Amituk Lake.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 211

itation onto the lake surface (Table 6). Of the influent

water, 86% was discharged at the outlet and 14% went

into lake storage. Because surface runoff was the

principal contributor to the total water input, it

followed that this medium also accounted for most

of the chemical loading. Surface runoff was respon-

sible for greater than 85% of the lake input of most

major ions and nutrients. The bulk of this chemical

input occurred during the spring freshet, for example,

by 14 July (Day 195), 86% of the gauged stream

inflow had introduced 91% and 79% of the HgT and

Table 5

Mercury content of calcareous sedimentary rocks from the

Paleozoic Era

Rock type Mercury ng g�1 Reference

Limestone/dolomite 12.1F3.5 This study

Limestone, Penn., USA 4–14;

Median 9

McNeal and

Rose, 1974

Shale, eastern Canada Mean 42;

median 19

Cameron and

Jonasson, 1972

Limestone, Russian Platform Mean 30 Ozerova and

Aidin’yan, 1966

Limestone/dolomite, Worlda 10–220;

Mean 40

Jonasson and

Boyle, 1972

a Age of rocks unknown.

Ca2+ input respectively from the 6 streams. Direct

precipitation onto the lake surface was an important

route for H+, accounting for 27% of the total lake

input, whereas ground water contributed 32% and

20% of the total SO42� and NO3

� respectively entering

Amituk Lake. The sum of the mass changes in the

lake water column and the lake output generally

equated with the lake input (i.e., output/input ~1.0).

Exceptions were H+ and nutrients, which were lost in

the lake water column resulting in outputs that were

less than the corresponding lake inputs, and TP, which

increased in the lake water column such that the lake

output was greater than the lake input.

The gauged stream input of HgT to Amituk Lake

was 3967F82 mg. With additional HgT inputs, the

total lake input was estimated to be 4713 mg, gene-

rating a HgT flux of 0.177 Ag m�2 year�1 (Table 7).

The lake discharge transported 2785F61 mg HgT out

of Amituk Lake whereas 761 mg HgT was added to

the lake water column. Calculated by difference, 1167

mg HgT was deposited to the lake bottom producing a

recent lake sediment flux of 3.088 Ag m�2 year�1. By

comparing the ratio of recent and historic Hg

concentrations in the sediment cores (i.e., 45/18) with

the ratio of the recent and historic lake sediment

Table 6

Mass budget for Amituk Lake

Gauged

runoffaUngauged

runoff

Snow on

lake ice

Ground

water

Precip to

lake surface

I. Sum

input

Gauged lake

outflow

Change in lake

water column

II. Sum

output

Output /Input

H2O�10�6 m3 5.238 0.540 0.075 0.331 0.022 6.206 5.344 0.862 6.206 1.00

H+ Eq. 45 5 11 2 8 70 38 1 39 0.56

Ca2+ kg 82200 8479 93 9805 19 100596 95277 5143 100420 1.00

Mg2+ kg 16136 1664 44 2802 12 20658 17826 3928 21754 1.05

Na+ kg 5306 547 41 700 27 6622 6549 1377 7926 1.20

K+ kg 784 81 5 94 4 969 943 68 1011 1.04

Alk kEq. 5167 533 6 594 1 6301 5904 885 6789 1.08

SO42� kg 6577 678 41 3381 19 10697 7378 3768 11146 1.04

Cl� kg 11969 1235 105 1429 74 14812 14812 490 15302 1.03

SiO2 kg 1683 174 18 298 2 2175 2200 �1703 497 0.23

NH4+–N kg 35 4 0.6 1 1 41 26 �9 17 0.41

NO3�–N kg 161 17 2 44 1 224 116 �81 35 0.16

DIC kg 60721 6264 88 7036 13 74122 68442 15446 83888 1.13

DOC kg 3509 362 72 219 10 4172 3513 722 4235 1.02

POC kg 508 52 25 42 10 638 418 64 482 0.76

TP kg 66 0.3 3 0.1 69 17 162 179 2.59

TN kg 638 9 80 4 731 572 191 763 1.04

Hg total mg 3967 409 108 132 94 4713 2785 761 3546 0.75

a Inputs of TP and TN in gauged runoff include the ungauged contribution. These were based on 1993 nutrient concentrations and are only

estimates of 1994 TP and TN loadings.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221212

fluxes, a historic lake sediment flux was calculated to

be 1.235 Ag m�2 year�1. This historic to recent

enrichment factor of 2.5 was then used to estimate a

historic HgT lake flux of 0.071 Ag m�2 year�1 and

historic HgT atmosphere flux of 0.228 Ag m�2 year�1

(Table 7). Burdens of total mercury and water

provided estimates of recent and historic concentra-

tions of 2.96 and 1.18 ng L�1 for atmospheric

deposition and 0.76 and 0.30 ng L�1 for the total

lake input (Table 7).

4. Discussion

4.1. Snowpack

Physical and chemical differences between the

shallow snowpack on the upland plateaux and the

Table 7

Summary of recent and historic Hg levels in the Amituk Lake watershed

Recent burden

(mg)

Recent flux

(Ag m �2 year�1)

Recent

Atmospheric deposition 15067 0.569 2.96 ng

Amituk Lake 4713 0.177 0.76 ng

Lake sediments 1167 3.088 45 ng

deep snowpack in the stream valleys may in part be

explained by two distinct periods of snow deposition.

Historical evidence from Cornwallis Island has shown

that snowfall is generally heaviest in the fall,

relatively constant over the winter and heavy again

in the spring (Schindler et al., 1974). Snow gauge

measurements at Resolute for the 1993/94 snow year

confirmed this pattern—35.6 mm of snow fell from

September to November 1993, only 4.3 mm from

December to February and 44.8 mm from March to

May 1994. Temporal differences in snowfall were also

supported by oxygen isotope analysis which showed

that the 18O compositions of the shallow and valley

snowpack were comparable to 18O values measured in

fall and late winter precipitation respectively at

Resolute during this period (Kinney, 1997).

We hypothesized that the shallow, early snowpack

incorporated a significant amount of aeolian calca-

concen Historic burden

(mg)

Historic flux

(Ag m �2 year�1)

Historic concen

L�1 6040 0.228 1.18 ng L�1

L�1 1881 0.071 0.30 ng L�1

g�1 467 1.235 18 ng g�1

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 213

reous dust derived from the highly exposed outcrops

and rubble of limestone and dolomite. This relatively

wet, calcium carbonate-rich snowpack was further

compacted and hardened by mid-winter storms, which

can be frequent and severe at this time of the year

(Schindler et al., 1974). The late winter snowfall was

deposited onto the slick, frozen surface of the

established snowpack and was readily redistributed

by wind action into topographical depressions. With

less rock exposure for physical and chemical weath-

ering, the Ca2+ and alkalinity content of the new

snowpack was less than that of the shallow snowpack.

The higher concentration of HgT in the valley

snowpack (4.21 ng L�1) compared to the shallow

snow cover (1.25 ng L�1) may have reflected variable

concentrations of mercury in the atmosphere. Meas-

urements of total gaseous mercury (TGM) at Alert

north of the study site peaked during the summer

months, were relatively constant from September to

February and decreased markedly from April to June

(Cheng and Schroeder, 2000). The decrease, triggered

by the March polar sunrise, was attributed to an

enhanced conversion of gaseous elemental mercury to

oxidized Hg in the atmosphere and was associated

with a period of significant ozone depletion. That the

increased deposition of atmospheric mercury was

registering in the snowpack was supported by results

from the bSurface Heat and Energy Budget in the

ArcticQ (SHEBA) project conducted aboard a research

vessel locked in the polar icecap moving between

758–768 north latitude and 1758–1808 west longitude(Lu et al., 2001). The SHEBA study documented a

fourfold increase in HgT levels in snow on the polar

icepack from winter to spring, comparable to the

concentration changes observed at Amituk Lake.

4.2. Streams

Because the snowpack was the main reservoir of

HgT and also the primary component of the hydro-

logical cycle in Arctic watersheds (Woo, 1998), HgTconcentrations in surface runoff at Amituk Lake were

essentially regulated by the dynamics of the spring

freshet. At the initiation of snowmelt and stream

flow, elevated HgT levels were observed in most

streams (the exception being where snow dams

delayed the delivery and allowed mixing of melt-

waters). Total mercury enrichment was also recorded

at Nettle Brook, Vermont, where the initial low flow

period of snowmelt generated a peak stream concen-

tration of 10 ng L�1 compared to subsequent levels

generally less than 3 ng L�1 (Scherbatskoy et al.,

1998). At Amituk Lake, stream concentrations of

DOC, major ions and soluble nutrients also peaked at

this time. A complementary study investigating

persistent organic pollutants at the study site revealed

that this chemically enriched first melt pulse also

included semi-volatile, non-polar compounds such as

hexachlorocyclohexane and endosulfan, two organo-

chlorine pesticides that have been introduced into the

Arctic via atmospheric transport (Wania et al., 1999).

Chemical fractionation in an ablating snowpack has

been recorded elsewhere (Jeffries, 1990) often using

melt collectors deployed beneath the snowpack, but

it is infrequently observed in surface runoff. Perma-

frost is such an excellent aquitard that the chemically

enriched melt phase flows directly into stream

channels. In more temperate locations, the ground

beneath a deep snowpack is often unfrozen. In this

case, the infiltrating snowmelt can displace soil and

groundwaters to the surface producing stream water

that may differ in composition from that of the

original snowmelt (Semkin et al., 2002).

In remote areas, the riverine transport of HgT has

been associated with both filtered (primarily DOC)

and particulate chemical phases (Hurley et al., 2001).

Elevated levels of HgT and DOC have been recorded

during spring runoff and have been attributed to a

flushing of wetland areas and the release of both

dissolved organic carbon and particulate matter

(Krabbenhoft et al., 2002). In a Lake Superior basin

study, two tributaries recording the highest HgTconcentration also had the highest levels of suspended

particulate matter during spring melt (Hurley et al.,

2001). During high stream flows accompanying

spring melt in Vermont, the dominant form of mercury

transport was as particulate Hg (Shanley et al., 2002).

The role of organic carbon in the mobilization of HgTat Amituk Lake was not clear, particularly in view of

the low organic carbon levels recorded at this site.

However, depending upon the flow conditions, high

HgT concentrations did appear to correlate with high

concentrations of either DOC or POC. As typified by

the chemographs from Rock Creek (Fig. 4), concen-

trations of both HgT and DOC were elevated at the

onset of snowmelt and decreased as the spring freshet

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221214

progressed. Whether the similar chemographs repre-

sented an bassociationQ of the two species or simply

reflected the same chemical fractionation process was

uncertain. After the initial spring melt period, stream

HgT concentrations generally declined and leveled off

to about 0.4 ng L�1 during the summer. Notwith-

standing this observation, HgT concentration spikes

were occasionally recorded in the streams following

the spring freshet. In most cases, the elevated HgTlevels were related to high concentrations of sus-

pended solids, POC and trace elements (Fe, Al, Pb).

Of 15 basin-wide samples (12% of the total number of

stream samples) displaying elevated HgT levels

following the initial snowmelt, 12 had suspended

solids concentrations ranging from 6.3 to 82 mg L�1

(29.8F26.9 mg L�1) and POC concentrations from

0.02 to 1.57 mg L�1 (0.36F0.45 mg L�1). These

levels compared to average discharge-weighted con-

centrations of 4.4 mg L�1 suspended solids and 0.10

mg L�1 POC for all stream samples. Cave Creek was

well represented in this sample pool having sustained

extensive streambed scouring and increased turbidity

when the snow dam collapsed and meltwater surged

down the stream channel. At a Vermont study site, a

similar correlation between HgT in stream water and

the organic fraction of suspended solids was attributed

to the affinity of Hg(II) for organic substances in

forest soils (Scherbatskoy et al., 1998). Particulate

organic carbon may be important in transporting HgTat Amituk Lake although the role of some inorganic,

mineral complex may also be significant as suggested

by the concomitance of elevated levels of HgT and

trace elements in this set of samples. Oxidized pyrite

nodules containing high concentrations of Fe and Hg

were noted in the bedrock at Amituk Lake. In

addition, elevated Hg and Fe levels were also

measured in the calcite matrix immediately surround-

ing the pyritic nodules. The increased presence of this

metal-enriched material in the streams during high-

erosional events and subsequent release of mercury

during sample preservation and storage may also have

contributed to the higher HgT levels.

4.3. Amituk Lake

Geology and climate were two main factors

influencing the chemical and physical characteristics

of Amituk Lake. The predominant calcareous sedi-

mentary rocks in the basin were prone to extensive

mechanical and chemical weathering in the harsh

Arctic environment. Measurements of the alkaline

composition that was imparted to both surface and

groundwaters in the basin corroborated the results of a

survey of 204 lakes in the Arctic Archipelago which

showed that, with the exception of some lower pH

lakes underlain by Precambrian bedrock, the majority

of the lakes had a calcium carbonate hard water

composition with relatively low carbon and nitrogen

content (Hamilton et al., 2001).

The spring freshet, the major hydrologic event in

the Canadian north, does have an impact on the

physico-chemical dynamics of Arctic lakes. During

this time, water from the ablating snowpack and from

the melting lake ice formed a cold, low-density layer

extending over the whole surface area beneath the ice.

Because of density differences between meltwater and

lake water, the stability of the meltwater lens was such

that minimal mixing occurred with the lake water

column. A substantial portion of meltwater and its

chemical content essentially traversed Amituk Lake

beneath the ice cover and exited at the outlet, at least

during the period of maximum stream flow. Not until

28 July (Day 209) – 2 weeks following the spring

freshet – did rising air temperatures and increased

solar radiation effect a warming of the influent stream

water and lake water, the disappearance of the ice

cover and the development of isothermal conditions in

the lake. It was at this time that the water column

turned over and physical and chemical mixing of

influent waters and lake water occurred. Similar

observations were recorded in small Arctic lakes by

Bergmann and Welch (1985), who emphasized that

the duration of the ice cover period was critical to the

timing and degree of lake mixing. Although not

common, the ice cover in some Arctic lakes can

remain intact throughout the summer (Schindler et al.,

1974), thus precluding any significant mixing of the

water column.

A comparison of chemical concentrations in lake

and stream water revealed that pH was higher and that

most major ions were enriched in Amituk Lake

compared to the influent and outflow streams. Similar

observations were made at Char Lake on the opposite

coast of Cornwallis Island (Schindler et al., 1974).

Several factors can account for this apparent paradox.

First, the formation of the thick ice cover (N2 m)

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 215

resulted in an increased concentration of solutes in the

underlying lake water. Through this process of

cryoconcentration, ion concentrations increased by

12% in Amituk Lake, which was somewhat less than

the 20% increase reported for Char Lake (Schindler et

al., 1974). Bergmann and Welch (1985) hypothesized

that these elevated concentrations would remain over

winter and would only be partially reduced through

the lake outflow during the spring freshet. Second, the

high flow-through of relatively dilute surface runoff

during the spring melt minimized any significant

dilution of major ion concentrations in the underlying

lake water. Third, during the late summer when

isothermal conditions prevailed and mixing was

occurring in Amituk Lake, the levels of Ca2+, Mg2+,

alkalinity and SO42� were steadily rising because of an

increasing contribution of ion-rich groundwater to the

streams and to the lake directly. In addition, the thaw

zone of the active layer was deepening such that

streambed flow now provided 22% of the water input

to Amituk Lake (compared to 1% during the spring

freshet, Kinney, 1997). As the enriched stream and

groundwaters entered Amituk Lake, extended mixing

of old and new waters resulted in a further increase in

concentration of these ions in the water column.

The elevated concentrations of Ca2+, Mg2+, alka-

linity and SO42� in lake water and in the influent

streams during the post-freshet period attested to the

importance of geochemical weathering and the role of

basin geology in determining the chemical composi-

tion of surface waters in the watershed. Some major

ions (K+, Na+, Cl�), nutrients (NO3�, NH4

+, SiO2,

DOC), H+ and total mercury did record comparable or

lower concentrations in Amituk Lake than in the

streams or lake outflow. This could be explained in

part by biological uptake of the nutrients or chemical

reactions (H+) in the water column as well as by

sedimentation (HgT) in Amituk Lake. However, the

obvious association of elevated levels of these

chemicals, particularly HgT, with snowmelt in the

influent streams and beneath the lake ice and the

unique chemographs displayed during the spring

freshet and post-freshet periods did suggest that the

snowpack was also a significant source of these

chemicals. Nitrate was somewhat unique in that

substantial lake inputs resulted from both the melting

snowpack during the spring and from the active layer

during the late summer, although net lake concen-

trations did remain below stream levels. The pattern of

steadily increasing NO3� concentrations in the streams

during the summer had previously been reported for

streams feeding Char Lake and was attributed to the

decomposition of vegetative matter, storage of NO3�

in the permafrost and release of NO3� during thawing

of the active layer (Schindler et al., 1974).

The surface layer of lake sediment cores C1 and C2

recorded Hg concentrations of 37 and 38 ng g�1,

relatively low values that may be linked to dilution

effects near the Gorge Creek inflow, the major source

of surface runoff for Amituk Lake. However in the

deepest section of the lake, sediment focusing may

have resulted in a higher Hg concentration (60 ng g�1)

in the surface layer of core C3. The existence of a low

energy depositional environment at site C3 was

supported by unpublished results of particle size

(67% clay, 30% silt) and organic carbon (0.67%) in

the surface 0–1 cm layer whereas results from site C1

(35% clay, 64% silt and 0.90% organic carbon)

suggested a higher energy environment. In consid-

eration of the natural variation in depositional

processes at the lake bottom, an average surface Hg

concentration from the 3 cores was used—a value 2.5

times greater than what may be considered the pre-

industrial, historic concentration (18 ng g�1) deeper in

the sediment profile.

4.4. Water and mercury mass budget

Despite the substantial area of the watershed and

the heterogeneity of the snowpack, the estimate of

the water content of the snowpack appeared

reasonable, particularly in view of the general

agreement with the cumulative precipitation quanti-

ties measured at Resolute in both the study year and

in 2 earlier years. Also, potential water losses via

sublimation from the snowpack were considered to

be negligible in this region (Woo et al., 1981). In

terms of the hydrologic budget for Amituk Lake,

approximately 86% of the total water input to

Amituk Lake was calculated from actual measure-

ments of stream flow and SWE in the snow on the

lake ice. The minimum uncertainty at a 95% degree

of confidence for stream discharge measurements

with a current meter has been reported as F5%

(Herschy, 1995). An additional degree of uncertainty

was inherent in the tabulation of other water inputs

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221216

to the lake. Surface runoff from the ungauged slopes

surrounding Amituk Lake was only an estimate, albeit

a reasonable one based on an areal apportionment of

the gauged stream flow. Groundwater input to the

lake was estimated at 0.331�106 m3, or 5% of the

total water inflow. The use of the Cl� concentration in

groundwater and the Cl� mass budget to estimate

QGW assumed that this ion behaved conservatively in

the lake, i.e., that input equaled output, and that Cl�

was neither lost to the sediments nor added to the lake

water column. This appeared to be a reasonable

assumption in that the 490-kg Cl� actually added to

the lake amounted to only 3% of the total Cl� output.

Furthermore, other analyses employing a more com-

plex hydrologic model and an isotopic mass balance

came up with an identical ground water contribution

to the total water input (Kinney, 1997). Unlike in

many other environments, evaporation was not

considered in the hydrologic budget for Amituk Lake.

Because of the extended period of ice cover,

evaporative losses from the lake surface were

estimated to be less than 1% of the water leaving

Amituk Lake (Kinney, 1997). In addition, water loss

through ground water outflow was considered to be

negligible because of the presence of the permafrost

aquitard.

The estimate of chemical inputs via atmospheric

deposition can be considered the weakest link in the

mass budget calculation for the watershed. Not only

was the chemical variability of the snowpack a

potential problem for quantifying the chemical

burden, but the deposition attributed to spring and

summer precipitation was calculated with a certain

degree of uncertainty. Because precipitation samples

were not collected for HgT, the chemistry of the

late-season, valley snowpack was used as a surro-

gate for the spring/summer precipitation chemistry.

In reality, at least 20% of this precipitation fell as

snow. In terms of total mercury, the selection of the

higher HgT concentration from the valley snowpack

may have biased the estimate of total Hg deposition

from the atmosphere on the high side. However,

summer measurements of total gaseous mercury at

Alert were approximately double the levels recorded

for TGM in the fall/early winter (Cheng and

Schroeder, 2000) when the shallow snowpack was

being formed. It would not be unreasonable to

assume that the higher TGM levels would have

resulted in relatively higher Hg concentrations in

summer precipitation.

The recent HgT flux from atmospheric deposition

in the watershed (0.57 Ag m�2 year�1) was similar to

the oceanic Hg flux of 0.68 Ag m�2 year�1 proposed

by Mason et al. (1994) for wet deposition at 708–908north latitude but much lower (by a factor of at least

10) than flux values reported for more southerly,

temperate locations in North America (Driscoll et al.,

1998) and in Fenno–Scandia (Lee et al., 1998). The

low recent HgT flux at Amituk was in part related to

the relatively low HgT concentration in precipitation

(~3 ng L�1) but more to the very low annual

precipitation quantity in the High Arctic. In terms of

the historic HgT flux from atmospheric deposition, the

low annual precipitation quantity also precluded a

direct comparison with pre-industrial flux values from

other sites. However, by using our estimate of the

historic Hg concentration in atmospheric deposition

(1.18 ng L�1) and a hypothetical annual precipitation

of 500–1000 mm (comparable to more temperate

areas), the historic, pre-industrial Hg deposition

would have increased to 0.6–1.2 Ag m�2 year�1. This

was less than the 2 Ag m�2 year�1 estimated for pre-

industrial atmospheric Hg deposition in many temper-

ate and boreal zones (Meili, 1995) but similar to the

pre-industrial HgT fluxes of 0.78 Ag m�2 year�1

recorded in the Upper Fremont Glacier in Wyoming,

USA (Schuster et al., 2002) and 0.5–1.0 Ag m�2

year�1 determined from ombrotrophic bogs in south-

central Sweden (Bindler, 2003). The difference in the

recent and historic Hg flux in atmospheric deposition

can be considered as anthropogenic in origin. The

anthropogenic Hg component of atmospheric deposi-

tion to the catchment, 60% at Amituk Lake, was less

than the relative estimates of 75% anthropogenic Hg

at 7 headwater lakes in Minnesota and Wisconsin

(Swain et al., 1992) and 70% at the Upper Fremont

Glacier in Wyoming (Schuster et al., 2002).

Of the estimated 15067 mg HgT deposited to the

watershed, 10,354 mg (69%) was retained within the

catchment and 4713 mg (31%) entered Amituk Lake.

Some of this mercury might have been lost by photo-

reduction of Hg2+ and Hg0 evasion to the atmosphere

(Lalonde et al., 2002), and some may have adsorbed

to surface materials. The retention is lower than the 84

to 92% reported for catchments in south-central

Ontario, Canada (Mierle, 1990), but given the extreme

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 217

differences in the characteristics of the watersheds the

difference is not surprising. With a further loss of

1167 mg HgT to the lake sediments, the net retention

in the combined catchment and lake basin increased to

77%, comparable to the 74% and 78% retention rates

reported for temperate lakes in the upper Midwest

USA (Engstrom et al., 1994) and in the Adirondacks

region of New York (Lorey and Driscoll, 1999)

respectively but less than the 94% retention calculated

for lakes in New Hampshire and Vermont (Kamman

and Engstrom, 2002). The estimate of the historic HgTburden in atmospheric deposition assumed that the

retention rate in the Amituk Lake catchment had not

changed over time. In one of the few studies

addressing this issue, an increase in the watershed

export of mercury from lakes with large catchment:

lake areas was more likely attributed to a decline in

the atmospheric deposition of Hg to the lake surface

and an increasing atmospheric component of the Hg

fluxes rather than a decrease in watershed retention

(Kamman and Engstrom, 2002).

The mercury budget for Amituk Lake was driven

by surface runoff. Of the total Hg input into the

lake, approximately 84% was transported via the

gauged streams. Direct measurements in the snow

on lake ice accounted for another 3%. Estimates of

HgT in surface runoff on the slopes surrounding

Amituk Lake amounted to 9% of the total input;

precipitation directly to the lake surface added

another 2% and groundwater 2.5%. Because ground-

water samples were not collected for HgT analysis, a

typical mid-summer stream concentration of 0.4 ng

L�1 was used to estimate lake inputs via this

medium. This was reasonable in that groundwater,

moving through permeable, subsurface streambeds,

was a major component of stream flow entering

Amituk Lake during the post-freshet period (Kinney,

1997). Despite the uncertainty associated with the

selection of a ground water HgT concentration, the

overall Hg input to Amituk Lake from groundwater

was not considered significant because of the

relatively low groundwater contribution to the total

water influx.

Partitioning of Hg in a lake basin may be affected

by various factors such as the watershed to lake area

(Meili, 1995), the biological productivity and organic

carbon content of lake water and the hydrologic flow

paths in the catchment (Landers et al., 1998). At

Amituk Lake, 59% of the HgT input was discharged

through the lake outflow. The hydrology of the

watershed as manifested in the mixing dynamics of

snowmelt with lake water during the spring freshet

was a prime control mechanism for the movement of

Hg in the lake basin (and presumably in other High

Arctic freshwaters). This was further demonstrated

with the results from a mass balance study of

organochlorine chemicals in Amituk Lake, which

showed a predominant (96% to N99%) snowmelt

source of the lake inputs and flow-through rates as

high as 98% for compounds whose sole source was

the atmosphere (Helm et al., 2002). Sequestration of

HgT in the lake sediments accounted for 25% of the

measured HgT input to Amituk Lake and generated

present-day and historic sediment fluxes of 3.1 and

1.2 Ag m�2 year�1. In an independent study at Amituk

Lake, 210Pb-dated sediment cores were used to

establish comparable HgT sediment flux values of

3.9 and 1.8 Ag m�2 year�1 for recent and pre-

industrial sediments (Lockhart et al., 1998). The ratio

of the present-day sediment flux to the historic

sediment flux was 2.5, a value consistent with

sediment flux ratios of 2.3F0.3 calculated for six

lakes in eastern Canada (Lockhart et al., 1998).

Sediment flux ratio values generally decrease westerly

into northern Canada and Alaska to b1.5 (Landers et

al., 1998) and increase southerly to values approach-

ing 3.5 in closer proximity to the industrial heartland

of North America (Lorey and Driscoll, 1999).

4.5. Geological mercury

The presence of mercury in the country rocks, the

ample exposure of easily weathered bedrock in the

catchment and the composition of the glacial till

which is derived from local bedrock underscore the

potential importance of geological mercury sources

in the Amituk Lake system. Mercury exists in the

carbonate bedrock at Amituk Lake at levels similar

to those reported for other calcareous sedimentary

rocks of a comparable geological age. Various

factors can influence the trace element composition

of carbonate rocks, including the physicochemical

environment of the original sedimentary basin, the

abundance and composition of organic and inorganic

(non-carbonate) components in the calcareous sedi-

ments and inorganic processes such as recrystalliza-

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221218

tion and ion leaching and/or replacement in the

mineral lattice (Wolf et al., 1967). If the assumption

is made that the analytical results from the 13 rock

samples were representative of the geological mate-

rial in the catchment, then the release of Ca2+ by the

dissolution of the carbonate rocks could be used to

infer a potential production of geological Hg. For

example, the lake mass budget revealed that

100,596-kg Ca2+ entered Amituk Lake during the

period of study. Based upon the average Hg content

of the bedrock, this could have resulted in a

proportional release of 1227-mg geological Hg, or

26% of the total lake HgT input. However, depend-

ing upon the form of Hg in the carbonate rocks, the

actual amount of mercury introduced into the surface

water and ground water could be quite variable. If

Hg behaved like certain other trace elements (e.g.,

Mn, Zn and Cu) and substituted for calcium in the

calcite crystal structure through surface reactions

such as sorption, co-precipitation and/or diffusion

(Temmam et al., 2000; Schosseler et al., 1999), then

the geological contribution to the lake HgT input

could be quite significant. However, the ability of

Hg(II) to form very stable bonds with reduced

sulphur species is probably the overriding factor in

determining the forms of Hg in the host rocks and

ultimately the availability of geological Hg in the

catchment. Present-day observations reveal that Hg

(II) preferentially binds with thiol and other sulphur-

containing groups in organic matter in soil/soil

solution and stream water (Ravichandran, 2004).

Thiol functional groups associated with organic

carbon are also implicated in the partitioning of

HgT in the colloidal phase and in the fate and

transport of Hg in freshwaters (Babiarz et al., 2001).

In more reducing environments such as may have

existed in the ancient sedimentary basins, Hg would

most likely have formed stable complexes with

inorganic sulphide although the role of organic thiols

in mercury binding under these conditions may also

have been important (Ravichandran, 2004). Sulphide

minerals containing Hg and other trace elements

have been observed in the bedrock at Amituk Lake

and have been reported at numerous locations on

Cornwallis Island (Gibbins, 1991). Assuming that

HgS solubility regulates the Hg concentration and

using a pH value of 8.32 and STotal=10�8 M, the

following equations can be used to estimate the total

soluble Hg in equilibrium with HgS in Amituk Lake

(formation constants from NIST Database, 2003):

Hg2þ þ 2HS� ¼ Hg HSð Þ02 K ¼ 1037:7

Hg2þ ¼ 2HS� ¼ HgS2�2 þ 2Hþ K ¼ 1023:2

HgS solidð Þ þ Hþ þ HS� ¼ Hg HSð Þ02 K ¼ 10�0:11

If [HgTotal]=[HgHS2�]+[HgS2

2�]~2[HgS22�], then

[HgTotal] would equal about 10�16.1 M or 0.000015

ng L�1. This estimate is markedly less than the ~0.3

ng L�1 measured in Amituk Lake or estimated for

historic stream water. The total S would have to be

increased to about 10�3.6 M, an unrealistic value, for

this model calculation to fit the measured Hg. If the

assumption of HgS solubility regulating the Hg

concentration is valid and the formation constants

for HgS species are correct, then the apparent

discrepancy between the measured and predicted

Hg concentrations may reflect the importance of

other Hg phases and species involved in Hg aqueous

geochemistry and/or the fact that the measured HgTcontains some colloidal-particulate Hg (Babiarz et

al., 2001). Without additional study of the minera-

logical form of mercury in the geological material in

the catchment and of the mercury speciation in

Amituk Lake, estimates of the geological contribu-

tion to the Hg mass budget remain uncertain.

5. Conclusion

This study investigated the biogeochemical and

physical cycling of major ions, nutrients and trace

elements in a High Arctic watershed. Because of the

natural occurrence of mercury in the bedrock and

surficial geological materials in the catchment, Hg has

been present in Amituk Lake since the lake was

created during the last glaciation. The mass budget

exercise provided some insight into the behaviour and

distribution of mercury and other chemicals in the

catchment and in Amituk Lake. Recent increases in

the atmospheric deposition of mercury have increased

the lake and sediment HgT flux by a factor of 2.5.

What impact this ultimately will have on the unique

ecosystem at Amituk Lake and at other Arctic

watersheds remains to be answered.

R.G. Semkin et al. / Science of the Total Environment 342 (2005) 199–221 219

Acknowledgements

The authors thank Dennis Gregor for initiating the

Amituk Lake mass balance studies and for inviting us

to join in the fun. Because pieces of the puzzle were

extracted from 3 field seasons, there are numerous

people that deserve our gratitude. For their dedication

and hard work in a exciting yet sometimes lonely and

inhospitable place, we acknowledge Peter Amarualik,

Julie Buchesne, Katrina Cove-Shannon, Michael Fox,

Jill Franklyn, Hillary Freitas, Bruce Gray, Pat Healey,

Ipeelee Itorchuk, Neil Jones, Shawn Kinney, Brenda

Koenig, John Kraft, Michael Mawhinney, Marie

Prchalova, Bob Rowsell and Camilla Teixeira. Don

Evans performed the Hg analyses at the Dorset

Environmental Science Centre. Laboratory assistance

was also provided by Don Kurylo and members of the

LRTAP facility at the Great Lakes Forest Centre in

Sault Ste. Marie, Ontario, by Paul Wilkinson and Lyle

Lockhart at Fisheries and Oceans Canada in Winnipeg,

Manitoba, and by Seprotech Laboratories in Ottawa,

Ontario. Computer support in data analysis and

graphics was provided by Fariborz Norouzian and

staff of the Graphic Arts section at NWRI. Jim Kramer

in the Department of Geology at McMaster University

provided valuable insight into Hg speciation at Amituk

Lake. The authors are also grateful to Russ Shearer and

others at Indian Affairs and Northern Development

Canada for their generous financial support through the

Northern Contaminants Program and the Polar Con-

tinental Shelf Project in Resolute for their excellent

logistical support. We thank Togwell Jackson (NWRI)

and two anonymous reviewers for their valuable

comments on earlier versions of this manuscript.

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