Long-term records of atmospheric deposition of mercury in peat cores from Arctic, and comparison ...

151 Pages·2017·7.07 MB·English

by  Nicolas Givelet

Long-term records of atmospheric deposition of mercury
in peat cores from Arctic, and comparison with bogs
Nicolas Givelet
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Nicolas Givelet. Long-term records of atmospheric deposition of mercury in peat cores from Arctic,
and comparison with bogs. Geochemistry. Universität Bern, 2004. English. ￿NNT: ￿. ￿tel-00009797￿
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Long-term records of atmospheric
deposition of mercury in peat cores
from Arctic, and comparison with
bogs in the temperate zone
Nicolas Givelet
PhD dissertation
February 2004
Institute of Geological Sciences
University of Berne
Long-term records of atmospheric
deposition of mercury in peat cores from
Arctic, and comparison with bogs
in the temperate zone

Inauguraldissertation
der Philosophisch-naturwissenschaftlichen Fakultät
der Universität Bern

vorgelegt von

Nicolas Givelet

von Frankreich

Leiter der Arbeit:

Prof. Dr. William Shotyk

Institut für Umwelt-Geochemie
Ruprecht-Karls-Universität Heidelberg

Von der Philosophisch-naturwissenschaftlichen Fakultät angenommen.

Bern, 5. Februar 2004 Der Dekan:

Prof. Dr. G. Jäger
Nicolas Givelet - PhD thesis - Berne, 2004

- Additional information -

Heidelberg, July 2005

This doctoral dissertation consists of an introduction and five chapters. The first four chapters are in
the form of manuscripts which have been now all published in international peer review scientific
journal.

Chapter 1:
Givelet N., Roos-Barraclough F., and Shotyk W. (2003) Predominant anthropogenic sources and
rates of atmospheric mercury accumulation in southern Ontario recorded by peat cores from three
bogs: comparison with natural "background" values (past 8,000 years). Journal of Environmental
Monitoring, 5, 935-949.

Chapter 2:
Givelet N., Roos-Barraclough F., Goodsite M.E., Cheburkin A. K. and Shotyk W. (2004)
Atmospheric mercury accumulation rates between 5900 and 800 calibrated years BP in the High
Arctic of Canada recorded by peat hummocks. Environmental Science & technology, 38, 4964-
4972.

Chapter 3:
Shotyk W., Goodsite M. E., Roos-Barraclough F., Givelet N., Le Roux G., Weiss D., Cheburkin
A. K., Knudsen K., Heinemeier J., van der Knaap W. O., Norton S. A. and Lohse C. (2005)
Accumulation rates and predominant atmospheric sources of natural and anthropogenic Hg and Pb
on the Faroe Islands. Geochimica et Cosmochimica Acta, 69, 1-17.

Chapter 4:
Givelet N., Le Roux G., Cheburkin A. K., Chen B., Frank J., Goodsite M. E., Kempter H.,
Krachler M., Noernberg T., Rausch N., Rheinberger S., Roos-Barraclough F., Sapkota A., Scholz
C. and Shotyk W. (2004) Suggested protocol for collecting, handling and preparing peat cores and
peat samples for physical, chemical, mineralogical and isotopic analyses. Journal of
Environmental Monitoring, 6, 481-492.

The following papers have evolved from collaboration during my master thesis (DEA Dynamique de
la Lithosphère, Grenoble) or my doctoral thesis:

Roos-Barraclough F., Givelet N., Martinez-Cortizas A., Goodsite M. E., Biester H., and Shotyk
W. (2002) An analytical protocol for the determination of total mercury concentrations in solid
peat samples. Science of the Total Environment, 292, 129-139.

Arnaud F.; Revel-Rolland M.; Bosch D.; Winiarski T.; Desmet M.; Tribovillard N.; Givelet N.
(2004) A 300 year history of lead contamination in northern French Alps reconstructed from
distant lake sediment records. Journal of Environmental Monitoring, 6, 448-456.

Le Roux G., Weiss D., Grattan J., Givelet N., Krachler M., Cheburkin A. K., Rausch N., Kober B.
and Shotyk W. (2004) Identifying the sources and timing of ancient and medieval atmospheric
lead pollution in England using a peat profile from Lindow Bog, Manchester. Journal of
Environmental Monitoring, 6, 502-510.
Nicolas Givelet - PhD thesis - Berne, 2004

- Table of contents -

Abstract…………………………………………………………………………………... 2

Introduction……………………………………………………………………………... 3

Chapter 1:
Predominant anthropogenic sources and rates of atmospheric mercury
accumulation in southern Ontario recorded by peat cores from three bogs:
comparison with natural “background” values (past 8,000 years)…………………. 13

Chapter 2:
Atmospheric mercury accumulation rates between 5900 and 800
cal. year BP in the High Arctic of Canada recorded by peat hummocks…………... 42

Chapter 3:

Accumulation rates and predominant atmospheric sources of natural and
anthropogenic Hg and Pb on the Faroe Islands since 5420 14C yr BP recorded
by a peat core from a blanket bog………………………………………………….. 57

Chapter 4:

Suggested protocol for collecting, handling and preparing peat cores and
peat samples for physical, chemical, mineralogical and isotopic analyses………… 89

Chapter 5:
Long-term records of atmospheric mercury deposition in peat deposits
from Eastern Canada: Post expedition field and status report……………………... 104

Appendix:
An analytical protocol for the determination of the total mercury
concentrations in solid peat samples……………………………………………….. A.1

1
Nicolas Givelet - PhD thesis - Berne, 2004

-Abstract-

Because of the strong tendency of significantly different from atmospheric Hg
mercury (Hg) to bioaccumulate in the food fluxes in the temperate zone. In pre-industrial
chain, one of the greatest challenges faced by times, therefore, the High Arctic was not more
environmental mercury research in the Arctic important as a sink for global atmospheric
is to quantify the relative contribution of mercury than the temperate zone. Therefore,
anthropogenic sources of mercury to the other processes have to be invoked as chief
contamination of this environment, as mechanism for transferring atmospheric Hg to
anthropogenically elevated mercury deposition the Arctic environment, possibly made more
over the past 150 years in Arctic ecosystems is efficient in recent years by environmental
potentially a serious environmental problem. changes, resulting in the mercury
To determine the magnitude of this concern, it contamination of the Arctic food chain.
is necessary to quantify the natural
“background” of atmospheric mercury The beginning of mercury contamination
deposition and its variation over a millennial- from anthropogenic sources dates from AD
scale period of time. A second problem is to 1475 at the Luther Bog in southern Ontario,
understand the role which is played by the corresponding to biomass burning for
unique climate of the Arctic on the deposition agricultural activities by Native North
of atmospheric mercury. Americans. During the late 17th and 18th
Total mercury concentrations were centuries, deposition of anthropogenic
determined in peat cores from the High Arctic mercury was at least equal to that of mercury
of Canada, the Faroe Islands and southern from natural sources. Anthropogenic inputs of
Ontario. The cores were dated using 210Pb and mercury to the bogs have dominated
14C. The mercury concentrations were used to continuously since the beginning of the 19th
calculate rates of atmospheric mercury century.
accumulation in the peat in order to quantify The records from southern Ontario and the
rates of atmospheric deposition of mercury in Faroe Islands show similar chronologies to one
the Arctic. In addition, rates of atmospheric another, with mercury accumulation rates
mercury accumulation in the Arctic were peaking in the 1950`s with 54 to 141 and 34
compared with peat cores from the temperate µg m-2 per year respectively. At both locations,
zone of North America (southern Ontario). in these (modern) samples, the Hg
concentration profiles resemble those of lead
Mercury concentration measurements and (Pb), an element which is known to be
age dating of two peat hummocks from immobile in peat bogs. The correlation
Bathurst Island, Nunavut indicate rather between these two metals suggests that the
constant natural “background” mercury flux of predominant anthropogenic source of Hg (and
ca. 1 µg m-2 per year from 5900 to 800 Pb) was coal burning. While Hg accumulation
calibrated year BP. The values are well within rates have gone into strong decline since the
the range of the Hg fluxes reported from other late 1950`s, Hg deposition rates today still
Arctic locations (Greenland and the Faroe exceed the average natural background values
Islands) but also by peat cores from southern by 7 to 13 times in southern Ontario. The
Canada (Ontario) which provide a record of increase in atmospheric mercury rates since
atmospheric Hg accumulation extending back the pre-industrial times in all these records is
to eight thousand years. Thus, pre- larger than the predicted by current global
anthropogenic Hg fluxes in the Arctic were not mercury cycling models.

2
Nicolas Givelet - PhD thesis - Berne, 2004

- Introduction -

This doctoral dissertation consists of an species contaminated by methylmercury
Introduction and five chapters. The first four (Wheatley et al., 2000). Environmental
chapters are in the form of manuscripts which mercury levels are thought to be elevated in
have either been published, accepted for Arctic, to generally increase with latitude, and
publication, in review, or in preparation; the to have increased over time (AMAP, 2002).
fifth chapter is an unpublished field report. Several hypotheses have been addressed
in a recent past to explain the contamination of
1. Introduction and background the Arctic environment. For instance, it has
been suggested that, as originally conceived
Mercury (Hg) is primarily of interest as a for some volatile organic compounds (Wania
long-range, persistent and toxic pollutant et al., 1993), there may be a latitudinal
because of its ability to bioaccumulate in the fractionation of mercury (Mackay et al., 1995)
food chain in the form of methylmercury which contributes to the continued
(Morel et al., 1998). Due to its high volatility, mobilization of these compounds from warmer
low chemical reactivity and low solubility in to colder climates (i.e. cold condensation),
water, elemental mercury (Hg°) makes up resulting in a natural geographical gradients in
approximately 98% of total atmospheric the atmospheric deposition rates. Mercury may
mercury and has a residence time in the condense over the Polar Regions due to the
atmosphere up to 2 years. This means that cold climate suggesting a natural high
mercury vapour can be transported far beyond deposition rate in Polar Regions where it is
the regions in which it is emitted (Schroeder et ultimately deposited and stored. Moreover,
al., 1998). Environmental mercury levels have record of atmospheric mercury deposited in a
increased considerably since the on-set of the peat core from NW Spain extending back
industrial age in the mid 1800’s due to the 4,000 years (Martínez Cortizas et al., 1999)
increase in fossil fuel burning. Coal burning provided evidence of a causal relationship
releases large amount of heavy metals such as between net Hg accumulation and Holocene
lead and mercury into the atmosphere. Also, climate change, with cold climate phases
industrial emissions to the atmosphere such as appearing to promote the accumulation of
mercury emission from chlor-alkaly factories atmospheric Hg in peat. Given this findings, it
and waste incineration increase the heavy is reasonable to expect that cold climate in the
metal burden of the atmosphere and the rates Arctic region may promote the natural
of atmospheric deposition to terrestrial and accumulation of atmospheric mercury, not
aquatic surfaces. Mercury is now present in a only from recent anthropogenic sources, but
various environmental media and food all over also in pre-anthropogenic times.
the globe at levels that adversely affect More recent discoveries suggest that the
humans and wildlife. Even regions with no Arctic experiences enhanced deposition of Hg
significant mercury releases such as the as part of related mercury depletion events
Arctic, are adversely affected, due to (MDEs) observed to occur each spring
transcontinental and global atmospheric (Schroeder et al., 1998). Gaseous elemental
transport of mercury. mercury (Hg°) in the Arctic atmosphere
undergoes photochemically driven oxidation
1.1. Mercury contamination of the Arctic during polar sunrise, probably by reactive
environment halogens, which converts elemental Hg to
reactive gaseous mercury (RGM) which
Exposures are thought to be increasing, subsequently deposits rapidly on snow as
especially among indigenous Arctic follows:
populations who consume fish and piscivorus
3
Nicolas Givelet - PhD thesis - Berne, 2004

Br + O → BrO + O (i) used to reconstruct historical records of atmo-
3 2
BrO + Hg° → Hg2+ + Br (?) (ii) spheric metal deposition (Boutron et al., 1994;
Boutron et al., 1995). In contrast to the lead
Some of the mercury deposited on the snow is record which is now well documented for
released to the environment at snowmelt, Greenland (Boutron et al., 1998), much less is
becoming available just as the Arctic known about the historical records of
ecosystem becomes biologically active in atmospheric Hg deposition. To date, there is
springtime. Evidence suggests that this is a only one study for North America reporting
recent phenomenon that may occur throughout Hg accumulation rates from a glacial ice core
the Polar Regions. This enhanced deposition (Schuster et al., 2002). The background metal
may mean that the Arctic plays a previously concentrations in these ice cores may be so
unrecognized role as an important sink in the low (sub-pg/g), however, that the studies are
global Hg cycle (Lindberg et al., 2002). severely challenged by generally inadequate
The impact of climate change on Hg analytical sensitivity and a variety of
dynamics is the third emerging issue. Changes contamination problems; sample deconta-
in physical climate in the past decades might mination becomes an integral part of this work
actually have a greater impact on the Arctic (Candelone et al., 1994). Only those few
Hg cycle than changes in global emissions: laboratories with extreme ultraclean conditions
decreasing trend in multi-year ice coverage, can even be considered for use in these kinds
related increases in annual ice coverage, later of investigation. In addition, the geographic
timing of snowfall and earlier timing of distribution of permanently frozen “snow and
snowmelt, increasing ocean temperatures, and ice archives” is limited to high elevations and
increasing atmospheric circulation and latitudes, thereby restricting such studies to
temperatures. Several data sets suggest that these areas.
there has been a recent increase in Hg levels in
Arctic biota despite a 20 year decrease in Lake sediments
global atmospheric Hg emissions of 30%
(Pacyna et al., 2002). Environmental changes Lake sediments have also been used as
may have made Hg pathways more efficient in archives of metal pollution (e.g. Dillons and
recent years by increasing transport of Evans, 1982; Evans and Dillon, 1982), and
photooxidants and production of reactive thee is a growing number of studies of Hg in
halogens in the Arctic. Although poorly lake sediments from Arctic and Subarctic
understood, these processes may be the chief regions (Lockhart et al., 1995; Lucotte et al.,
mechanism for transferring atmospheric Hg to 1995; Hermanson, 1998; Lockhart et al., 1998;
the Arctic food chain. Bindler et al., 2001). However, lake sediments
Environmental archives such as snow and are influenced by both atmospheric and non-
ice, lake sediments and peat bogs provide a atmospheric inputs (Norton et al., 1986). Also,
record from which we can reconstruct the interpreting the lake sediment record may be
natural contribution of heavy metals, complicated by such processes as chemical
determine rates of pollutant deposition and diagenesis related to sulphate reduction at the
assess the rates of change that have occurred sediment-water interface, bioturbation,
with increasing industrialization. resuspension and sediment focusing (Norton et
al., 1987; Norton et al., 1990). Furthermore,
1.2. Archives of atmospheric metal decreased metal retention in the sediments due
deposition in the Arctic to recent acidification of lakes may further
affect the historical trends (Dillon et al.,
Snow and ice 1986).

Quantitative measurements of trace metals
in snow and ice from Greenland have been
4
Nicolas Givelet - PhD thesis - Berne, 2004

Fig. 1. Peatland distribution expressed as a proportion of the land surface for different parts of the world,
based on Gore (1983) and Lappalainen (1996). This map provides a general idea of where peatlands are an
important part of the landscape and is based on incomplete data. Redrawn from Lappalainen (1996) by
permission of the International Peat Society in Charman (2002).

Peat bogs Greenland as archive of atmospheric metal
deposition (Shotyk et al., 2003).
Unlike glacial ice which is restricted to
alpine and polar regions, peatlands are widely 2. Objectives
distributed across the globe (Fig 1),
accounting perhaps 5% of the land area of the The ultimate objective of this research
Earth (Kivinen et al., 1981; Matthews et al., was to bridge the knowledge gap between the
1987). The surface peat layers in lack of temporal trends and deposition loads of
ombrotrophic, raised bogs are hydrologically mercury from long-range atmospheric
isolated from the influence of local transport in the Arctic of Canada and to try to
groundwaters and surface waters, and are fed understand the role which is played by the
exclusively by atmospheric deposition unique climate of Arctic on the geochemical
(Damman, 1986). There have been numerous cycle of mercury. To accomplish this, the
studies using peat bogs of the temperate zone main objective was to assess and quantify the
(especially Europe and NE North America) as changing rates of atmospheric mercury
archives of atmospheric metal deposition deposition on a millennial-scale period of time
(Glooschenko et al., 1986; Jones et al., 1993; in the Arctic and to compare this with a record
Steward et al., 1994; Shotyk, 1996; Shotyk et from the temperate zone in North America.
al., 1997; Weiss et al., 1999). To date, with This was accomplished using physical and
the exception of superficial report by Headley chemical analysis of peat cores from
(1996), and the brief report by Brown and hummocks peat on Bathurst Island (Chapter 2)
colleagues (1994) which found most trace and ombrotrophic Sphagnum peat bogs in
metal concentrations below the lower limit of southern Ontario (Chapter 1).
detection, there is only one published study
which use Arctic peat deposits from southern
5
Nicolas Givelet - PhD thesis - Berne, 2004

Specifically, we 4) identified the predominant anthro-
1) quantified the changing rates of pogenic sources of Hg and Pb to the
atmospheric mercury deposition in Faroe Islands using Pb isotopes.
southern Ontario from the modern
period through the pre-industrial 3. Results
period, into the pre-European times,
2) estimated the extent of anthropogenic These studies are based on the
contribution to the mercury deposition measurement of geochemical profiles in peat
flux using the ratio of this element to cores and on their interpretation as archives of
selenium (Se) and bromine (Br) as past environmental change. Major and trace
reference elements for mercury, element concentrations in peat were analysed
3) identified the predominant sources of using x-ray fluorescence spectrometry (XRF).
anthropogenic Hg contamination by Mercury was measured in solid peat samples
comparison of the modern by atomic absorption spectroscopy (AAS)
chronologies of lead and mercury, using an analytical protocol in-house
4) quantified the rates of atmospheric developed (Appendix A). The relative degree
mercury accumulation in the High of decomposition of the peat was determined
Arctic of Canada, where such data was by colorimetric measurement of alkaline peat
not available, focusing toward the rates extracts. Isotopic ratios of lead contained in
of natural atmospheric mercury peat were measured using inductively coupled
accumulation, plasma mass spectrometry. Dating of the peat
5) examined the potential for “cold was carried out using three different
condensation” effect for Hg. techniques: conventional 14C atomic mass
spectrometry dating, the bomb pulse curve of
A second objective of this research was to 14C (AMS) and 210Pb dating by gamma assay
determine the anthropogenic contribution to using the constant rate of supply model.
the mercury deposition flux to the Faroe
Islands and assess the importance of mercury 3.1. Hg deposition in North American peat
from volcanism and mantle degassing as cores
potential local or regional source of natural
mercury to the environment. This was Southern Ontario
accomplished using physical, chemical and
isotopic analysis of peat cores from Peat cores from three ombrotrophic bogs
ombrotrophic Sphagnum peat bogs on the in southern Ontario provide a complete,
Faroe Islands (Chapter 3). quantitative record of net rates of atmospheric
Hg accumulation since pre-Industrial times:
Specifically, we Sifton bog in the city of London, Luther bog
1) quantified the net rates of atmospheric which is a rural location, and Spruce bog
mercury accumulation on the Faroe which is comparatively remote, in Algonquin
Islands using recent and pre-industrial Park. For comparison with these modern
peats, values, a peat core from Luther bog extending
2) separated the mercury inventory into back 8,000 years was used to quantify the
its natural and anthropogenic natural variations in Hg fluxes for this region,
component using bromine and and their dependence on climatic change and
selenium as reference elements to help land use history.
to characterise pre-anthropogenic The average background mercury
inputs accumulation rate during the pre-
3) compared the chronologies of anthropogenic period (from 5,700 years B.C.
anthropogenic mercury accumulation to 1470 AD) was 1.4 ± 1.0 µg m-2 per year.
with that of Pb, The beginning of Hg contamination from
anthropogenic sources dates from AD 1475 at
6