7
NICKEL IN SOILS AND
VEGETATION OF GLACIATED
TERRAINS
A. N. Rencz and W. W. Shilts
Geological Survey of Canada, Ottawa, Ontario, Canada
I. Introduction
1.1. Major differences in soils of glaciated and unglaciated landscapes
1.2. Analytical techniques
2. Glacial and Derived Sediments
2.1. Till and derived sediments
2.2. Till and till provinces
2.3. Nickel in glacial sediments
2.4. Postglacial weathering
3. Glacial Dispersal of Nickel
3.1. Introduction
3.2. Examples of dispersal by modem glaciers
3.3. Small-scale dispersal at a northern townsite
3.4. Local dispersal in the Appalachian Mountains
3.5. Regional variation of nickel in till across a complex bedrock
terrane: the Canadian Shield
4. Nickel in Vegetation of Glaciated Areas
4.1. Introduction
4.2. Mechanisms of nickel uptake by plants
Soil pH
Metal interactions
Concentration of nickel
Biological variation
Nickel in various plant organs
Seasonal variation of nickel
152
152
153
154
154
154
158
158
161
161
162
164
165
170
175
175
177
177
177
178
180
181
181
151
152
Nickel in Soils and Vegetation of Glaciated Terrains
4.3. Examples of effects of glacial dispersal on flora
Ferguson Lake, District of Keewatin (96°SO'W; 62°53'N)
Thetford Mines, Quebec
Rankin Inlet, District of Keewatin
5. Concluding Statement
Acknowledgments
References
182
182
183
184
185
185
185
1. INTRODUCTION
1.1. Major Differences in Soils of Glaciated and
Unglaciated Landscapes
.
..Ii•
II
•
Factors that control nickel distribution in the soils of glaciated areas differ in one
important aspect from those that control its distribution in soils elsewhere: the
detritus that fonns most of the unconsolidated cover of glaciated regions has been
physically eroded from bedrock, crushed and mixed with other bedrock debris, and
transported by glacial ice. Thus in addition to unweathered components from
underlying bedrock, the glacial sediments, such as till, glaciofluvial gravels, and
glaciolacustrine clays, have strong mineralogical, and therefore chemical, aff'mities
with bedrock located ''up-ice" along lines of glacial flow.
In this chapter the expression "glacial soil" should be taken to be interchangeable
with the expression "glacial sediment," unless otherwise defined. Glacial or related
sediments, although soil-like in their lack of consolidation and in their significant
content of fine material, are the parent material for true soils, fonned on them in
postglacial or interglacial times.
Glacial origin imparts several important differences to the chemistry of the soils
of glaciated landscapes, when compared to unglaciated landscapes where soils are
fonned by chemical, aeolian, or fluvial processes:
1. Enrichment of an element in the soil is not confined just to the area where that
element is enriched in the bedrock; glacial transport may disperse the components containing that element over wide areas, areas several times larger than
those underlain by the source rocks.
2. Dispersal by glaciers is usually independent of drainage divides except in mountainous areas where valley glaciers are often confined to ancestral valley systems.
Thus, with the exception of some valley glaciers, nickel-bearing detritus from a
given source can be distributed throughout several drainage basins.
3. Because glacial soils at any given location are. composites of detritus eroded
from several, often genetically diverse bedrock sources, minerals and therefore
chemical components of several origins may be found together in one sample.
Such seemingly chemically · incompatible groupings as chromium-uranium-zinc
may occur, for instance, where a glacier has traversed bedrock including acid,
Introduction
153
basic, and ultrabasic igneous strata in close proximity, a lithologic assemblage
that is not uncommon on the Canadian Shield.
The finest portions of glacial soils, particularly the chemically reactive clay
(<2 µrn) sizes, are predominantly composed of easily crushed bedrock detritus,
such as phyllosilicate (micaceous) minerals, hematite, and serpentine. These
components are glacially abraded to clay sizes by virtue of their soft or easily
cleavable nature and are generally not the products of weathering, as are the fine
fractions of soils in nonglaciated areas. That is not to say, however, that some
true clay minerals and other products of preglacial, interglacial, or interstadial
weathering are not eroded and mixed with clay sized detritus produced by
glacial grinding of fresh bedrock or clast surfaces. In addition to these easily
comminuted minerals, other, harder components, such as quartz and feldspar,
can also be found in the clay sizes of glacial soils; although they dominate the
silt and sand sized fraction, glacial abrasion has reduced some of these harder
minerals to clay sized detritus.
S. In glaciated carbonate terrains and in areas where the bedrock contains sulfides,
olivine-serpentine, or other minerals that are broken down during the first stages
of weathering, unweathered glacial soils can contain these components in abundance. For this reason the mineral assemblages of glacial soils are complex in
direct relationship to the complexity of the bedrock terrane eroded by their
depositing glacier. Unlike unglaciated areas that are mantled by residual soil,
selective chemical removal of labile components by weathering processes has
occurred only in the postglacial solum. Llkewise, there has been no concentration of the secondary weathering products that are characterized by enhanced
exchange capacities, such as Fe-Mn hydroxides or oxides, or true clay minerals.
1.2. Analytical Techniques
The type of analysis and sample preparation used to determine nickel concentra·
tions are important to define in any discussion of the nickel geochemistry of
glaciated areas. This is because the physical crushing of bedrock leads to significant
mineralogical partitioning by particle size; thus chemical partitioning by particle
size also occurs. If too large a range of grain size is chosen for analysis, textural
variations can significantly affect apparent concentrations (Shilts, 1971, 1973). For
this reason our analyses of till are routinely performed on the <2 µm size fraction,
which we consider to be the most chemically active or reactive portion of glacial
soils. We have also completed many analyses on the silt plus clay fractions
(<64 µrn) and on the heavy mineral porti()n (specific gravity> 3.3) of the fine sand
fraction of selected till samples for comparison. The analyses of the silt plus clay
fraction should yield nickel values that are comparable in magnitude to "bulk"
analyses or analyses of the "-80 mesh" fraction that is commonly used in geochemical exploration research. We have rejected the latter type of analysis because,
except in proximity to a strong nickel source, such as an ore body or source of
pollution, natural textural variations make sample-to-sample comparisons difficult.
I
154
Nickel in Soils and Vegetation of Glaciated Terrains
Geochemical analyses are carried out in a commercial laboratory using standard
atomic absorption techniques. The till fractions submitted from Geological Survey
laboratories were leached in hot concentrated HN03 -HCl, a treatment that is considered to remove most available nickel from the clay sized fraction.
2. GLACIAL AND DERIVED SEDIMENTS
2.1. Till and Derived Sediments
The most characteristic and widespread sediment in glaciated areas is till, a mixture
of rocks, sand, silt, and clay eroded by and deposited more or less directly by
glacial ice. Till deposited by slumping of debris from the surface of uppermost
debris bands of the ice during glacial advance or retreat is variously referred to as
ablation till, supra or superglacial meltout till, or flow till (Boulton, 1970a, 1970b;
Dreimanis, 1976). It may contain mudflow structures resulting from water sorting,
and its clasts may be larger and more angular than other till. The other principal
type of till is called, variously, lodgment, basal, or basal meltout till and is formed
by lodging or melting out of the dense load of debris carried at the base of a glacier
(Dreimanis, 1976). There may be significant compositional differences between the
two types of till at any given location (Shilts, 1976).
In glaciated areas most other sediments are derived from already deposited till or
from till-like debris in transport in a glacier by means of glaciofluvial or postglacial
fluvial erosion and sorting, by deposition of fine components in lakes or marine
environments, or by aeolian reworking. The water or wind deposited sediments in
glaciated areas can be thought of as derivatives of till, having undergone some
secondary vector of transport in addition to the original glacial vector, and having
suffered some degree of chemical weathering during transport in the post- or
nonglacial weathering environment. Thus to a great extent, derivative sediments,
such as varved clay, esker gravels, or modem stream and lake deposits, share much
of their inorganic mineralogical and chemical character with the nearby glacial till
with which they were deposited or from which they were derived. The implication
of this is that, in glaciated regions, chemical characteristics of derived sediments are
also affected directly or indirectly by glacial transport.
2.2. Till and Till Provinces
Throughout the rest of this chapter, most discussions of nickel distribution are
based on analyses of till. We·present data on Canadian tills primarily, but cite a few
examples from other glaciated areas. In Canada, till covers much of the 95% of the
country that has been glaciated. However, in the Arctic Archipelago and in parts of
northern Baffin Island and Boothia Peninsula the glaciers were apparently coldbased and effected little erosion of the preglacial landscape. As a result, much of
the unconsolidated cover in this terrain is apparently true residual soil, formed
Glacial and Derived Sediments
ISS
more or less in situ and transported short distances downslope by solifluction
processes. This residuum is commonly mantled by glacial erratics, proving glaciation, but other obvious glacial deposits are rarely found over it.
The glacial sediments deposited by the major North American ice sheets can be
grossly subdivided on the basis of suites of physical and chemical properties
imparted to till by glacial mixing of lithologies typical of the large bedrock
provinces of the continent (Scott, 1976). Histograms depicting typical nickel
contents of the clay fractions of till from some geologically defined provinces are
presented in Figure 1. In general, tills from sedµnentary bedrock terrane have
narrow ranges of nickel concentrations, whereas tills from complex, crystalline
bedrock terrane, such as the Canadian Shield, have a wide range. Tills from areas
with significant outcrops of ultrabasic bedrock, such as occur in the Appalachians,
have distinctly bimodal nickel distnbutions, the higher mode representing tills
lying on or "down-ice" from the ultrabasic bedrock.
LEGEND
I. Pr•combrion shield
Z. Appalacllian mountains
3. Pal•oioic HdirMnlary basins
3A. Area of cold based 9laci9ra
4 . Mtlsazoic - Pal•azoic basins
!I. Cordill9fa
Figure 1. Nickel concentrations in cJay ( <2 µm) fractions of till samples from various geologic
regions in north-central North America. Each histogram based on 100 to 1000 samples. Samples
in Quebec collected in Jegion of ultrabasic outcrops (see also Figure 6).
Somerset Island
..
30
f
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20
A
..
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10
l
0
20 40 60 80 IOO 120 140 l60 180 200 >200
Ni (ppm)
..
Bylot Island
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20 40 60 80 IOO 120 140 l60 180 200 >200
Ni (ppm)
..
Southeastern Keewatin
C
30
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20 40 60 80 100 120 140 160 180 200>200
.
Ni (ppm)
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Ni (ppm)
156
Figure 1. (Continued)
Hudson Boy Lowlands
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Fipre 1. (Continued)
157
l 58
Nickel in Soils and Veaetation of Glaciated Terrains
2.3. Nickel in Glacial Sediments
The distribution of nickel in various types of bedrock is discussed elsewhere in this
volume (see Duke, Chapter 2, this volume). Although nickel contents of glacial
sediments do not necessarily correspond absolutely to concentrations in bedrock,
partially because selected size ranges are used for analysis and partially because till
at any site is diluted by debris eroded from various types of rock that occur up-ice,
nickel is present in amounts that vary directly with changing bedrock sources.
Although nickel is present in small to moderate amounts in acid igneous rocks and
in metasedimentary and sedimentary rocks (see discussion by Duke, Chapter 2,
this volume), it occurs in concentrations far above the crustal average in basic and
ultrabasic igneous rocks. Where a glacier has eroded nickel-enriched zones in basalts,
gabbros, serpentinized periodotites, and similar basic or ultrabasic igneous rocks, or
their metamorphic equivalents, nickel-enriched glacial debris may be spread out in
the form of a glacial dispersal train. As noted above, such a train may cover an area
many times larger than the source outcrops. The decline in nickel concentration
with increasing distances down-ice from the nickel source can be plotted in the form
of a ••dispersal curve." A dispersal curve characteristically has two distinct
segments. The region of rapidly declining high nickel values near the bedrock source
is termed the ..head" of dispersal. The region of less rapidly declining moderate
values of nickel is termed the ..tail" of dispersal. The tail is generally several times
longer than the head, and the overall form of the dispersal curve is that of a negative exponential curve (Shilts, 1976).
Nickel occurs in unweathered glacial sediments in the same mineral phases as
those in which it is found in rocks. Where a glacier has tapped sources of nickel in
basic igneous rocks, for example, the nickel is usually concentrated in nickel and
nickel-iron sulfide grains. In these cases, nickel-enriched silicate minerals are not
common. Where a glacier has overridden ultrabasic rocks, nickel may still be present
in sulfide grains, but its presence in silicates such as olivine, serpentine, amphiboles,
biotite, and talc can lead to very high bulk nickel compositions in till or derived
sediments. In this latter case, high nickel contents may be associated with varying
amounts of asbestiform serpentine.
2.4. Postglacial Weathering
Drift enriched in nickel is usually weathered (oxidized and leached) to some extent
in its uppermost 1 to 4 m. Nickel that is held in sulfide minerals is generally redistributed in this zone of weathering by destruction of the sulfides.
Profiles of nickel concentration in the sand sized heavy (specific gravity > 3.3)
mineral fractions of vertical sequences of till samples show that nickel concentration, which is largely in the sulfide minerals, drops radically at the depth below the
surface where visual signs of weathering first appear (this is true for all elements
that commonly combine with sulfur) (Figure 2). Profile sampling programs carried
out in the Appalachian Mountains, Nova Scotia, and the District of Keewatin yield
Black Lake, Quebec
Thetford Mines, Quebec
0
ZOO 400 600 800 IOOO
100
900
noo
l300
Nickel (ppm)
0
IOO 200 300
o
'°
too
~
ea
Concentrotion in heavy minerol froc1ion
c-1ro1ion in cloy
Nickel (ppm l
Hartlen Point,Oortmouth,Novo SCotio
Mc19ute Rivet' ,Dittrict of Keewatin
0
20
40
60
Nickel (ppm)
Ill Nickel in heovy rninlfOll (•·II- > 3.3)
0 Nickel In Cloy (
0
100
< 2pm)
200
Nickel (ppm)
FJ81Ue 2. Typical weathering profiles lhowing redistribution of nickel in clay and heavy
mineral fractions of nickel-poor and nickel-rich till.
159
160
Nickel in Soils and Vegetation of Glaciated Terrains
similar results. In the Applachians, the clay sized fraction of the weathered drift
appears to adsorb some of the nickel released by weathering of the sulfide fraction,
but not as readily as it does other products of sulfide destruction, such as copper.
This phenomenon is reflected by an increase in nickel content of the clay (<2 µm)
fraction upward from the base of the zone of oxidation (Figure 2).
A section exposed in a sea cliff near Dartmouth, Nova Scotia illustrates the strong
contrasts in sulfide-bound nickel (as reflected by analyses of sand sized heavy
minerals) between two physically distinct tills. Although the depth of oxidation
cannot be estimated visually because of the red hue of the upper till, it is well
documented by a sharp decrease in nickel in the sulfide fraction at a depth of 4 to
5 m. The nickel in the clay component apparently is not significantly augmented by
the nickel released as a result of sulfide weathering.
In a section through a drumlin located in the zone of deep, continuous permafrost on the Maguse River, west of Hudson Bay in the District of Keewatin, nickel is
present in relatively low amounts in the sulfide fraction (30 to 60 ppm Ni). Consequently, although a sharp decrease in nickel can be seen in the heavy mineral
0
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8 g 8 g ~ g 8g 8
ppm Ni
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Concentration of element in era,.
Concentration of element In <63u (250me1hl fraction.
Sample tile
Fagure 3. Variation of nickel and chromium in clay and silt+ c}ay fractions of serpentine-rich
till approximately 2 km down-ice from ultrabasic bedrock near Thetford Mines, Quebec.
Glacial Dispersal of Nickel
161
fiaction at the pennafrost table, little or no enrichment of nickel in the clay
fiaction can be observed. The pennafrost table is analogous to the water table in
temperate areas in that it divides the zone of oxidation and leaching above (active
layer in areas of pennafrost) from the zone of little or no weathering below
(perennially frozen soil).
If nickel is bound within the structures of silicate minerals, its behavior under
weathering conditions is more difficult to define. Primary nickel-bearing silicates,
derived from unweathered bedrock by glacial erosion, are generally much more
resistant to weathering (at least with respect to the relatively short 4000 to 12,000
years of postglacial weathering that characterizes most glaciated areas) than are
nickel-bearing sulfides, which can be destroyed by exposure to exidation over a
period of a few years. When the silicates are broken down, however, it is difficult
to see where or even if the nickel released migrates. This is largely because before
weathering, the various silicates are apportioned preferentially to various size ranges
within the drift as .a result of their varying resistance to glacial comminution by
virtue of their widely varying physical properties. Thus soft serpentine is preferentially enriched in the clay sized fraction, whereas harder olivine and amphiboles
occur preferentially in coarse silt and sand. As a result of the nickel-bearing
silicates' presence in all size ranges, it is difficult to separate silicates that have
adsorbed nickel released by weathering from nickel-bearing silicates that were
glacially eroded from an ultrabasic outcrop. A profde measured through the upper
few meters of a nickel-rich "serpentine" till near Black lake, Quebec suggests that
nickel is progressively removed from the clay sized fractions upward into the lower
parts of the solum (Figure 3).
3. GLACIAL DISPERSAL OF NICKEL
3.1. Introduction
Most published discussions of the significance of glacial processes in the interpretation of nickel distribution have been concerned with mineral exploration projects
and therefore deal with nickel variations over small areas in which abnonnally high
bedrock concentrations of nickel are localized in potential orebodies (e.g.,
Nurmi. 1976; Puustinen, 1977; Wennervirta, 1968). An exception to this was a
program carried out by the Danish Geological Survey in which nickel variations
were determined systematically over a wide area in Denmark for environmental
purposes (Binzer, 1974). May and Dreimanis (1973) also carried out a systematic
study of regional variations of nickel concentrations in an effort to differentiate
tills deposited by various glacial lobes that flowed off the Canadian Shield onto the
nickel-poor Paleozoic bedrock of southern Ontario.
Because it is difficult to synthesize the exploration studies into a meaningful
discussion of regional variations, we have chosen to describe in this chapter our own
examples of nickel variations in glacial deposits in several geologically disparate
regions of Canada, with the assumption that the principles and variations described
162
Nickel in Soils and Vegetation of Glaciated Terrains
herein can be applied or extrapolated to glaciated areas elsewhere. We have further
chosen to discuss the nature of nickel variations at three geologically meaningful
scales: (1) variations in nickel concentration at a detailed level where detectable
dispersal is of limited extent, and samples of glacial deposits are collected at intervals of 100 m or less around discrete bedrock nickel sources that presented areas of
hundreds of square meters to glacial erosion; (2) variations in nickel con<'.t'ntration
at a local level where nickel-bearing lithologic units, such as ultrabasic or gabbroic
rocks, measure tens of square kilometers or less, detectable dispersal is measured in
tens of kilometers, and samples are collected at intervals averaging just over a
kilometer; and (3) variations in nickel content at a regional level, where bedrock
sources of nickel and areas of nickel-enriched glacial deposits occur over areas
measured in hundreds of square kilometers and samples are collected at intervals of
10 km or more.
Our discussion concerns mainly nickel variations in till, the most common glacial
sediment, and the sediment from which the major part of the inorganic portions of
all other glacial and postglacial sediments are derived through water, wind, or
gravity sorting. For discussion of typical relationships of these derived sediments to
their parent till in areas we discuss, the reader is referred to papers by Shilts
(1973); Shilts and McDonald (1975); Shilts (1976), Klassen and Shilts (1977);
Dil..abio (in press), and Klassen (1975).
In addition to discussing the areal variations of nickel concentrations in the
surficial environment of glaciated areas, we present a brief discussion of vertical
variations in sections cut through glacial sediments. These types of variations can be
broken down into (1) primary variations, consisting of variations among various
stratigraphic units or variations within a single stratigraphic unit resulting from
shifting-ice flow trajectories through one or more glacial events, and (2) secondary
variations caused by weathering or other diagenetic processes acting on glacial
sediments after deposition (discussed above).
3.2. Examples of Dispersal by Modern Glaciers
Studies of nickel dispersal in the modem glacial environment are understandably
rare. In 1977 a study was begun of dispersal of trace elements by glaciers that drain
the highly metamorphosed Precambrian rocks that underlie the central highland
ice caps of Bylot Island, off the northeast coast of Baffin Island. One glacier on the
island, Aktineq, flows out of the Precambrian highlands across approximately
10 km of nickel-poor Cretaceous and Tertiary sandstones and siltstones. Although
specific sources of nickel are not known in the Precambrian terrane, it is assumed
that the Precambrian rocks contain significantly greater background concentrations
of nickel than the younger rocks over which the lower part of the glacier flows.
Dispersal maps and curves (Figure 4) show that the average nickel contents of the
clay sized fractions of till in the lateral moraine of this glacier decrease in a regular
way toward its snout. Dispersal plots of chromium, which varies sympathetically
with nickel on this and nearby glaciers, are shown for comparison. The nickel-
~
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AKTINEQ
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DISTANCE UP-ICE FROM SNOUT (km)
Dilpersal patterns and curves for nickel and chromium in clay fractions of till from
...me of Alctineq Glacier, Bylot Island, Northwest Territories (78°4S'W; 72°SS'N).
163
164
Nickel in Soils and Vegetation of Glaciated Terrains
enriched clay fractions of the glacial deposits associated with Aktineq glacier clearly
illustrate the contrasts created by glacial dispersal. The nickel content of the clay in
glacial debris is -so to 100 ppm; the nickel content of the clay in underlying
Cretaceous-Tertiary bedrock ranges from <l to 25 ppm (seven samples of various
lithologies). Thus in this case nickel concentrations measured in the surficial environment have been augmented significantly by the process of glacial dispersal and
deposition of nickel-rich Precambrian debris on nickel-poor Cretaceous-Tertiary
bedrock.
3.3. Small-scale Dispersal at a Northern Townsite
The townsite of Rankin Inlet, located in the zone of deep continuous permafrost
at 62° 48' latitude on the west coast of Hudson Bay, was developed to service a
nickel mine that operated in the late 1950s and early 1960s. The nickel ore
comprised sulfide minerals that occur as a lens in a serpentinite (Pelzer, 1950;
DiLabio and Shilts, 1977). Detailed sampling in and adjacent to the townsite
revealed that the town is built over till that is enriched in nickel that was glacially
dispersed southeastward from the serpentinite body (Figure 5). It is clear that
l
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~
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pp111
Nickel
•
< 201
•
201. 250
•
251 • 350
•
>350
~
•
••
••• <::>
•
•
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Figure 5. Dispersal pattern of nickel in clay fractions of till at Rankin Inlet, District of Keowatin, Northwest Territories. Nickel was mined from serpentinite at site of abandoned mine
shaft (modified from DiLabio and Shilts, 1977).
Glacial Dispersal of Nickel
165
elevated nickel contents in the clay fractions of till samples from Rankin Inlet are
largely due to glacial dispersal from the nickel-rich rocks that host the nickel
mineralization. Copper, chromium, and cobalt show similar 'dispersal patterns, for
they are also typically enriched in the body of ultrabasic rock that contains the
nickel-rich sulfide lens. This example underscores the importance of estimating
patterns of glacial dispersal before beginning mining activities in glaciated regions,
so that naturally enhanced metal levels may ·be differentiated from pollution
effects associated with mining and ore processing.
3.4. Local Dispersal in the Appalachian Mountains
The ophiolitic suite of rocks at Thetford Mines, Quebec includes significant
amounts of nickel-rich serpentinized periodotite and pyroxenite. Nickel is enriched
in serpentine, which is a major component of these ultrabasic rocks, and nickel
occurs in high concentrations in olivine and enstatite from which the serpentine was
derived by metamorphic processes (Nickel, 1959, 1971). Nickel is also present in
the volumetrically less important phases awaruite (NiFe) and heazlewoodite
(NiFe) 3 S2 (Nickel, 1959;Chamberlain, 1966).
Nickel makes up, on the average, 0.2 to 0.25% of the ultrabasic rocks of the
Thetford area. Chromium, cobalt, iron, and magnesium are also significantly enriched in the ultrabasic rocks compared to most other bedrock in the Appalachians.
Because of the soft nature of the ultrabasic rocks, resulting from their high
concentrations of serpentine minerals, and because the ultrabasic bodies form
hills that were exposed to glacial erosion, a great deal of ultrabasic detritus was
eroded from the ophiolitic outcrops near Thetford Mines. The glacially eroded
detritus was dispersed in the form of a train of nickel-rich glacial debris that extends
for over 80 km down-ice from the ultrabasic outcrops. This example of nickel
dispersal is perhaps one of the finest examples of glacial dispersal in the world. The
natme and shape of the train have been discussed in detail (Shilts, 1973, 1975,
1976), and the train has served as a model for interpreting glacial dispersal in
general. Maps showing dispersal of nickel and associated elements (Figure 6),
indicate clearly the compositional influence of the relatively small outcrops of
ultrabasic rock on the soils of a large area of glaciated terrain.
Figure 7 shows dispersal curves for nickel in clay fractions and in selected coarser
fractions of till along the axis of the dispersal train. In the clay (<2 µm) fraction of
till, the nickel is probably largely present in serpentine group minerals, which,
because of their soft, easily abraded nature, are preferentially glacially comminuted
to very fine sizes. In fact, some samples of till within 2 km of the ultrabasic source
contain 0.2 to 0.23% nickel in the clay fraction, indicating that this fraction is
almost totally composed of ultrabasic debris (mostly serpentine) with little or no
dilution by surrounding bedrock types. This is a graphic example of mineralogical
and chemical partitioning resulting from the physical process of preferential glacial
erosion and comminution of a soft mineral, serpentine, to its terminal grade
(Dreimanis and Vagners, 1971). In the silt and sand sizes serpentine and associated
0
2
4
6km
Ni~
r·
~::
.?/
······················..
\~
···... c._,..,
·....·.
:.....~
:::.:~/
'/._,
<~
/ >
...··
..•···:,, ......~..r··
.,.+-'
,,.. I
~
Q
~
Cr (ppm)
c
--.
/
-~
..
".
./ /
... ....... SI·
~,
P
i
.
\
I
i
\
(
\,
\
Figure 6. Glacial dispersal patterns of Ni, Co, and Cr in silt plus clay ( <63 µm) fractions of
till in Thetford Mines area of Quebec. Maps based on analyses of approximately 800 samples
evenly spaced within area outlined by dotted lines.
166
Figure 6. (Continued)
167
Nickel in Soils and Vegetation of Glaciated Terrains
168
1500
1400
1300
1200
1100
IOOO
......E
....I
l&I
li:
u
z
900
Ultraba1ic Outcrop
C-2200 ppm Nil
Nicloet In ctar fraction ( c211111 l
Nickel In lilt and cio, fraction (cS411111 I
800
700
Nickel In
600
~•
lilt fraction ( 4411111-8411111)
500
400
300
200
100
0
MILES
Figure 7. Dispersal curves for nickel in various fractions of serpentine till of Thetford Mines
area. Note that nickel is significantly enriched in clay fraction.
.,
nickel-bearing minerals are not so concentrated, being diluted principally by quartz
and feldspar eroded from nonultrabasic country rocks. Consequently, nickel levels
are significantly lower in the coarser fractions of till.
The elevated nickel concentrations in till in the dispersal area have significant
effects on postglacial sediments, such as stream or lake sediments, that are derived
wholly or in part by erosion of the unconsolidated till. For instance, modern stream
sediments in the state of Maine, located over 100 km from Thetford, across a major
drainage divide, contain anomalous amounts of nickel and chromium in areas where
the ultrabasic dispersal train is presumed to cross the border (Chaffee et al., 1970;
Shilts, 1976)•
Other factors that affect the understanding of glacial dispersal of nickel in the
Thetford Mines region are the ice flow histories of the various glaciers that deposited
the several till sheets identified in the area and the postglacial and interglacial
weathering that affected the till sheets. It is known, for instance, that the penultimate glaciation of the Thetford Mines region commenced when westward-flowing
glaciers entered the region from the east, presumably from an independent ice cap
centred on the eastern Appalachians of the Gaspe Peninsula, Maine, and/or the
Maritime Provinces (McDonald and Shilts, 1971 ). During glaciations preceding and
following the ''ice cap" glaciation, ice flowed from the Canadian Shield southeastward, the last major glaciation forming the southeastward-trending ultrabasic train
from Thetford Mines. Within the region covered by the dispersal train, the uppermost till sheet is markedly enriched in nickel compared to the till deposited by the
westward flowing ice, which passed over no significant ultrabasic outcrops (Shilts,
1978a) (Figure 8).
Several profiles of the surface till have been sampled both up-ice and down-ice
from the ultrabasic outcrops. In those sampled up-ice, nickel is largely present in
Glacial Dispersal of Nickel
169
0
G>
G>
G>
0
I
e
I
I
30 40 &O
I
10
I
90
I
110
I
130
I
160
Nickel (ppm of- 63,.. fraction)
Fipre 8. Profile of nickel concentrations in three till units at Samson River, Quebec. Ice flow
associated with Chaudiere Till was generally east to west across bedroclc terrain with no ultrabasic outcrops. Ice flow during deposition of Lennoxville tills was from north or northwest.
Nickel in Lennoxville till originates from vicinity of Thetford Mines, approximately 85 km
northwest of the section. (SOURCE: from Shilts, 1978a.)
sulfide minerals derived from volcanic rocks that occur northwest of Thetford
Mines. Figure 2 illustrates the unstable nature of the sulfide phase, which is concentrated in the heavy mineral fraction of sand separated from till. At the Petit Lac till
section, jbst north of the ultrabasic outcrops at Thetford Mines, the reaction of
nickel sulfides to oxidation is similar to the reactions shown in Figure 2 (Figure 9).
At this site, however, the last glacial flow was directed northward, toward the St.
Lawrence River, and debris that had been in transport toward the southeast was
redirected northward over the site and deposited. Thus the upper part of the profile
170
Nickel in Soils and Vegetation of Glaciated Terrains
Petit Lac ,Qu6bec
..
!
....i
•
.2...
"'
1•
~
TILL
2
D
ic
3
0
100 200 300 400 500 600
Nickel (ppm)
e Nickel in heavy mineral• (1.9. >3.3)
0 Nickel in cloy (< 211m l
Figure 9. Nickel in clay and heavy mineral fractions of till at Petit Lac, Quebec. Increase of
nickel concentration in clay fraction results from shifting trajectory of ice flow. Decrease of
nickel in heavy mineral fraction results from oxidation of nickel-bearing sulfide grains.
here shows a much more significant increase of nickel in the clay fraction than can
be accounted for by adsorption after weathering. The increase is interpreted to have
little or no relationship to the weathering of sulfide grains, but is thought to be due
to shifting directions of ice flow-a phenomenon that can be detected in many till
sections that lie close to a strong bedrock source of nickel.
At East Dover, Vermont, a fourfold variation in nickel content of the clay fraction is noted through two thick sheets of lodgment till located about 2 km
down-ice from a dunite (olivine-rich) ultrabasic body (Figure 10). The causes of the
consistent shift in concentrations through this unweathered section are probably
either shifts in ice flow trajectory from the source outcrops to the site through time
or progressive covering or uncovering of the dunite source by a glacier transporting
nickel-poor detritus from barren rocks up-ice. Samples were not collected from the
weathered zone at the top of the section.
3.5. Regional Variation of Nickel in Till Across a
Complex Bedrock Terrane: The Canadian Shield
A profile of nickel concentrations in till from cores recovered from boreholes 6 to
20 m deep, drilled at approximately 10-km intervals, was determined for a
2900-km long transect of the Canadian Shield (Figure 11). The samples were
Glacial Dispersal of Nickel
171
Nickel in till section, East Dover, Vermont (U.S. A.)
ABLATION TILL
~
LoclQment Till
~ PrOQlocial LoM Sediment•
•
LAKE I
G
Till Sample
•
Lall• Sediment Sample
.....
f•
!
=
•
a.
0
•
LAKE 2
G
LAKE 3
1
0
200
400
600
800
•
1000
Ni (ppm) in clay (c2um) fraction
Figure 10. Nickel in clay fractions of till sheets approximately S km down-ice from dunite
(olivine-rich) bedrock in Appalachian Mountains of southern Vermont. Large variations in
nickel concentration probably reflect shifting ice flow trajectories during till deposition. Note
compositional similarity of intercalated lake sediments. (Samples collected by C. W. White.)
originally collected by the Polar Gas Consortium for geotechnical tests along a
proposed gas pipeline route. Each point on the profile represents the average nickel
concentration of clay fractions of several till samples from a single borehole. All
samples are from depths greater than 2 m (to minimize weathering effects), and the
bars extending from the points indicate the range of variation encountered in the
hole. If more than one till sheet was encountered in a borehole, analyses from each
sheet are separated. This unique set of data gives an indication of the magnitude of
regional variations in nickel concentrations produced by glaciers that homogenized
"er
HUD SO
BAY
N
-;.. -.-
-----;._..,_
....
...... ...........
. . . . . ~of--iliottiftfroctioR
"-·
.._
......... •tlnftorill
.......
C7' _.,....
_
_
- ·-
---------------Em------o-...----~-­
...
Figure 11. Profile of nickel concentrations in clay fractions of till samples from > 2 m depth in boreholes across the central part of the Canadian Shield. Letters on figure refer to areas discussed in text.
(Samples courtesy of Polar Gas Pipeline Consortium.)
!O
IOO
r ..
........r-~~~~-r~-r~~~~..~·~·~~~~~~~~~~~~...~"":...
.. ..
' . ..
'·
..
.. t;\
.~
..
i)·.
.. .
sAY
,..,,
--___
~
........._........ ..
CJ ....,. -' •'-'_...
....... ,. . ,.-,1wl
..
..·
-
tnl
~
.... •:1,00o.000
-~-
12. ._....,... diotribOtio• of nld<•I _.......... in olaY
Sh"1d· Niok••-"""'tio., ;n
to 3000 evenlY spaced samples.
174
--0
motlo" ol tm of th< -
°"".,..of•"'""' -•Ung"'"""" on 2500
Nickel in Vegetation of Glaciated Areas
175
or less bisects this sampled area, and the Rankin Inlet townsite lies at the eastern
edge.
It can be seen that most of the till samples contain less than 80 ppm nickel in
their clay fractions. There are large regions, however, where many till samples
contain significantly more nickel, reflecting one or more of the following condi·
tions: (1) an enhanced content of nickel in all rocks of the region of enrichment;
(2) significant areas of nickel-enriched strata within the bedrock units (such as basic
extrusive or intrusive rocks, ultrabasic rocks); and/or (3) many individual zones of
nickel-rich sulfide mineralization. On this scale of sampling, the second and third
factors would make a region appear to be enriched in nickel throughout because of
homogenization caused by glacial erosion and mixing. It is beyond the scope of this
chapter and, indeed, beyond the present state of our knowledge, to discuss the
origins of most of the areas of nickel enrichment shown on Figure 12. However,
where the line of borehole samples passes through the region shown on the figure,
correspondence of nickel anomalies C1, near Baker Lake and ~ near the Prince
Albert Group can be seen to be related to large regions of nickel enrichment on
the map.
As with other examples p1esented in this chapter, the point of presenting these
data is not necessarily to explain the origin of the anomalies but to demonstrate the
magnitude of natural variations of nickel concentration related to glacial homogenization of bedrock sources of nickel. Furthermore, the higher nickel values imparted
to till by glacial erosion of bedrock regions with relatively higher nickel contents
than adjacent regions can overlap, through the process of glacial transp0rt, onto
adjacent regions where bedrock is not rich in nickel. Conversely, nickel-poor debris
can be carried onto nickel-rich bedrock, diluting the locally derived nickel-rich
detritus and thereby suppressing nickel concentrations in the local soils.
4. NICKEL IN VEGETATION OF GLACIATED AREAS
4.1. Introduction
The concentration of nickel in plants is proportional to variations in nickel concen·
trations in glacial soils and thus reflects the regional and local variations described
earlier in this chapter. The principal factors that differentiate patterns and mecha·
nisms of nickel concentration in glaciated in comparison to nonglaciated areas are
(1) the influence of glacial dispersal of nickel-rich debris over areas much larger
than the outcrop areas of the nickel-bearing source rocks and (2) the prominence of
unweathered, physically comminuted detritus in the fine fractions of glacial soils.
The first factor may influence the species composition or vigor of plant communities over wide areas. The second factor may influence the exchange of cations be·
tween soil and root tissues.
In addition to the two principal factors described above, several other soil
conditions peculiar to glaciated terrains can influence vegetation patterns and metal
176
Nickel in Soils and Vegetation of Glaciated Terrains
uptake. The variety of glacial and postglacial sediment types that are likely to occur
over a given area exert a profound influence on species composition of plant communities, due primarily to differences of soil drainage and intensities of soil-forming
processes. These effects usually exert a more easily discernible influence on local
vegetation patterns than any local variation in metal levels. However, the differing
physical properties of glacial sediments, and the differing soils that form on them as
a result, can potentially release metals to root systems in different ways. A second,
chemical and mineralogical peculiarity of glacial soils relates to the physical mixing
of mineral grains from diverse bedrock sources by glacial erosion, transportation,
and deposition. As described elsewhere in this chapter, in geologically complex
areas such as the Canadian Shield, it is not unusual to find metal-bearing mineral
grains typical of a granitic terrane mixed with those of, for instance, an ultrabasic
terrane. In soils where the glacial dispersal trains from these two rock types are
superimposed, such petrologically incompatible mineral assemblages as molybdenite
(MoS2 ), cassiterite (Sn02 ), chalcopyrite (CuFeS2 ), chromite (Cr02 ), serpentine
{Ni-bearing silicate, M&6S40 10{0H)8 ), and awaruite (Ni-Fe alloy) could occur together. Thus the role of one metal in the enhancement or inhibition of plant uptake
of another metal may be difficult to define in glaciated areas in comparison to nonglaciated regions where elements tend to be associated by virtue of a common
chemical environment of rock or soil formation.
In most glaciated areas, both the soils and the flora are ''young," having had le~
than 10,000 to 12,000 years to achieve equilibrium with their local environment.
In the case of the true solum developed on glacial soils, this means that many of the
more labile mineral and rock components, destroyed to considerable depths by
long-term weathering in nonglaciated regions, are still present and available for soilplant interactions. Primary sulfide minerals, olivine, serpentine, and calcareous minerals are some examples of these labile components. Furthermore, the secondary
Fe-Mn oxides-hydroxides and clay mineral products produced by long-term weathering, with their high potential for exchange reactions, are only in the first stages of
development in most glacial soils.
The tendency toward immaturity of the flora of the relatively young glaciated
terrain results, in many instances, in community species compositions that are
much more sensitive to short-term climatic fluctuation than to either local metal
variations or local differences in soil/glacial sediment types.
The relatively harsh climate of much of the world's glaciated terrain is a further
inhibiting factor in the breakdown of the more labile glacial soil constituents, retarding the release of both nutrients and metals.
Although many studies of nickel uptake by plants have been undertaken in glaciated regions, few, if any, have been integrated with glacial dispersal data. Most studies have been carried out on flora growing on glacial sediments and postglacial soils
lying directly on nickel-rich bedrock such as the ultrabasic rock bodies in the
Appalachians, Sweden, or Scotland (Shewry and Peterson, 1976; Lag and Bolviken,
1974). Studies have also been carried out in areas where soils are known to be contaminated by nickel, such as around Sudbury, Ontario {Whitby et al., 1976). In this
section, we intend first to present some of the principles of transfer of nickel from
Nickel in Vegetation of Glaciated Areas
177
soil to plant, then to present results of three studies carried out by Rencz in the
vicinity of glacial dispersal trains of nickel in the Canadian Arctic and in the Appalachian region of Quebec. As with the data presented on the effects of glacial dispersal on nickel concentrations in soils, we hope that these results can be used as
examples of response of plants to nickel-bearing glacial soils and can be extrapolated to predict responses in other glaciated areas.
4.2. Mechanisms of Nickel Uptake by Plants
Nickel is a nonessential trace element that occurs in trace amounts in most plants.
Where nickel exceeds background levels, inhibitory effects are obvious, except for
those plants that have evolved a tolerance to nickel excesses. Inhibitory effects of
nickel originating from natural sources (i.e., nonanthropogenic) are potentially significant in view of the relatively high concentrations of nickel that can exist in dispersal trains, the large areas of dispersal, and the high toxicity of nickel.
The most · critical factors to consider in evaluating the impact of nickel on an
ecosystem are the uptake and accumulation of nickel in various plant organs. These
mechanisms are affected by the amount and form of nickel in the soil and dictate
the effects of nickel on plant production and, to the extent that plants serve as
foodstuff for higher organisms, determine effects to the entire food chain.
The transfer of nickel from the soils to the plant depends primarily on (1) soil pH,
(2) metal interactions, and (3) concentration of nickel. The effect of organic matter
on the uptake is complex and has been covered elsewhere in this volume.
Soi/pH
It is well known that uptake of nickel is enhanced by a reduction in pH, especially
when pH is reduced below 6.5. The effect is due to the breakdown of iron and manganese hydrous oxides, which form stable complexes with nickel (Khalid et al.,
1977). The release of nickel from these sites facilitates the movement of nickel into
the plant root and thereby accounts for higher levels of accumulation. As in other
soils, pH can vary significantly in glacial sediments, especially where sulfides or
other minerals that yield acid conditions upon oxidation are present (Lawrey,
1978).
Metal Interactions
Studies have recognized the importance of metal interactions on nickel uptake.
Anomalous levels of one metal are usually associated with anomalous levels of one
or more other elements. For example, nickel in serpentine-rich soils is typically
associated with elevated levels of iron, cobalt, chromium, and magnesium. In glaciated areas, however, a great variety of petrologically unrelated minerals, and therefore metals, are likely to occur together as a result of glacial mixing.
Interactions between metals, as defined by Olsen (1972), are mutual or reciprocal
effects that affect plant growth. For instance, the concentration of one element
may affect the level of accumulation of other metals or may modify the toxic ef-
178
Nickel in Soils and Vegetation of Glaciated Terrains
fects of other elements (Beckett and Davis, 1978). Beckett and Davis, (1978) state
that the nickel-zinc interaction and nickel-copper interaction are additive; that is,
varying concentrations of zinc or copper neither reduce nor increase the effects of
nickel. This suggests that toxic effects of nickel are independent of those produced
by copper or zinc. In contrast, lizuka (1968) concluded that zinc reduces the toxic
effects of nickel and Mizuno (1968) states that iron and copper reduce nickel toxicity. The latter authors also consider that the reduction of nickel toxicity by zinc,
iron, and copper facilitates the uptake of greater volumes of nickel. Beckett and
Davis (1978) also state that zinc and copper may enhance the uptake of nickel.
In glaciated terrains with anomalous levels of nickel in soil, Rencz (I 979) has
shown significant correlations among elements in plant tissue. Positive correlations
were noted between nickel-copper and nickel-zinc at Ferguson Lake and Rankin
Inlet (District of Keewatin), and significant nickel-chromium correlations occurred
at Thetford Mines (Quebec). It is possible that the significant correlations reflect
the strong relationships between these elements in the soil. However, antagonistic
effects between elements may permit higher levels of nickel to be accumulated before toxicity symptoms develop (Beckett and Davis, 1978). This interrelationship
of metals may be significant to organisms higher in the food chain as higher levels
of nickel in plant tissue provide for more nickel to move through the food web.
Concentration of Nickel
•
It is well established in the literature that plants accumulate nickel and other heavy
metals in response t«? their availability in the soil, but quantitatively, soil-plant relationships are different depending on the species. Figure 13 identifies four species
types, each of which reflects the level of nickel in the soil, yet differs in its absolute
levels of nickel uptake. Metal-tolerant species (Type A) have evolved a tolerance
unique to one metal and are able to accumulate considerable amounts of nickel
without being inhibited by its presence (Antonovics et al., 1971). These species
have a relatively steep nickel accumulation curve, accumulate high levels of nickel,
and have no threshold of nickel accumulation. A nickel-tolerant species is likely to
be found growing only on nickel-rich soils.
There is varied opinion about the existence of species that can exclude nickel
(avoidance-tolerant, Type B). It has been suggested by Epstein (1972) that certain
species tolerate high levels of heavy metals in the soil by exluding their uptake,
probably through a form of metal chelation. Ernst (I 976) doubts the existence of
such a mechanism, however, concluding that the rate of uptake may be reduced by
an alteration in the cation exchange capacity of the roots. It does seem probable
that some species can control the rate of uptake of certain elements, particularly
toxic elements like nickel. The accumulation curve of avoidance-tolerant species
would flatten out at a threshold of nickel accumulation. The threshold would correspond to a toxicity concentration which, if exceeded for any reason, would kill
the plant.
There is evidence that some plants without a specific metal tolerance can also tolerate anomalous levels of nickel, probably through an ability to survive at greatly
reduced metabolic rates (general-tolerant, Type C) (Rencz, 1979). The general pat-
Nickel in Vegetation of Glaciated Areas
179
~
l
,
c
0
-..
z
/
,,
/
I
(C)
,,
/
/
/
HiQh
c
0
/
/
/
0
(.)
,,
/
~
8c
(8)
(A)
Hi9h
BockQround
·co>
c
..
0
~
0
/
/
/
/
BackQround
Soil Ni Concentration
Figure 13. Hypothesized representation of soil-plant nickel relationships. A, Metal-tolerant
species; B, avoidance-tolerant species; C, general-tolerant species; D, Intolerant species. Dashed
lines indicate that species are not common at that concentration of niclcel.
tern of nickel uptake in these types of plants would be similar to avoidance-tolerant
species. However, in this case the tlueshold is the result of a reduced uptake rate.
Rencz has observed that at relatively high concentrations in the soil (> 1000 ppm)
several arctic species displayed a conspicuous decrease in nickel concentrations
(Figures 13, 14). The decrease merits further study to ascertain its cause and its
importance.
The majority of plants are probably nickel-intolerant species (Type D). As illustrated in Figure 13 these species would be restricted to soils of relatively low nickel
content.
To summarize the four types of plants; Types A and B have evolved a specific tolerance to nickel, Type A by virtue of an ability to mask nickel toxicity and Type B
reducing nickel uptake tluough its root system. With these characteristics Types A
and B would most likely be restricted to soils of high nickel content where they
would be at a competitive advantage. Type C species are plants that survive on
nickel-rich soils, but without a specific tolerance to nickel, their growth is inhibited.
Type D species have no or limited ability to survive on nickel-rich soils.
General-tolerant species (Type C) are particularly important in glacial terrain because nickel in soils of dispersal trains does not generally occur at such high levels
180
Nickel in Soils and Vegetation of Glaciated Tenains
•
• •
•
153·
:
90 !:slandulosa
-·-...
•• •
•
•
•
60
30
•
!: nlgrum
60
•
•
20
• •
•
0
•
•
••
40
• •
••
0
157·
•
0
E
a.
a.
0
go0 •
0
80
160
lb
..
0
240 560
•
0
80
160
24flM
z
c
Ill
~
.
• •
60 L. groenlancllcum •
-
•
40
•
•
20
•
•
•
60 ~ uliginosum •
• •
•
40
•
-:
•
•
20
• •
•
00
0
1
0
•
•• • •
• • •
••
oogo
0
•
=
80
160
240 ! 60
0
0
0
SOIL Ni
80
160
...
240560
(ppm)
Figure 14. Relationship between nickel concentrations (ppm in dry weight) in the CUirent
year leaf growth of four arctic plants versus nickel concentrations (total) in soil at Ferguson
Lake, Northwest Territories.
that plants with a specific metal tolerance would have a competitive advantage. The
dominance of these species would also be predicted in northern areas because the
relatively young flora has not developed members that are commonly recognized as
metal-tolerant species (Brooks, Chapter 15, this volume).
Biological Variation
In addition to a specific set of environmental factors in glacial soils, the level of
nickel in plants depends on unique plant properties, including species variation, organ variation, and seasonal variation. We have just discussed broad groupings of
species with specific responses to nickel toxicity, and Brooks presents a review of
variation in nickel content among species in this volume (Chapter 1S); this section
will summarize variations in nickel levels among organs and with changing seasons.
Nickel in Vesetation of Glaciated Areas
181
Nickel in V01'/ous Plant Organs
The data on distribution of nickel in various plant organs may be biased by study
conditions which are typically at low or very high concentrations of nickel. Further
studies could benefit from investigation of a broad range of nickel concentration.
From available information it appears that nickel tends to accumulate in roots,
owing to its transport as a relatively immobile metalloorganic complex (Tiffen,
1971). This is supported by Cataldo et al. (1978a), whose experiments on soybeans
demonstrated that after 24 hr., nickel is concentrated in root tissue followed by
leaves= stem > pods ~ seeds. Similarily, Shewry and Peterson (1976) report mean
values of 3536 and 756 ppm nickel (in ash) in root and stem tissue of Agrostis
stolonifera growing on serpentine-rich (nickel-rich) soil. Significantly higher levels
in roots than in other organs have been reported by Cataldo et al. (1978b). However, a few studies (for example, Brooks, 1972) reported higher levels in aboveground tissue than in belowground tissue. The differences among species may be
due to strategies, or lack of them, in heavy metal tolerance, or to seasonal variations.
Seasonal VOl'kltion of Nie~/
Seasonal variation in the content of nickel may be sigruflcant, especially when nickel
is found at anomalous levels. In a study of two arctic species growing on soils highly
mineralized with nickel, Rencz (1979) has shown a slight but consistent increase in
nickel content of all tissues thrnugh the season. -The rate of increase was faster in
leaf tissue than in root or stem tissue (Table 1). In Betula glandulosa Michx. the
concentration of nickel in roots increased 6.2% through the season, while leaf and
stem tissue increased 10.3% and 15.8%, respectively. The results suggest that the
root retains a high percentage of nickel in the spring, whereas in the fall there is an
enhanced movement to aerial tissue. Rasico (1977) has demonstrated a similar phenomenon for Thlaspi cepeaefolium growing on zinc deposits. The ability of these
Table I. Mean Concentration of Nickel in Root, Stem, and Leaf Tissue from
Ferguson Lake at Three Sampling Dates
Ni Concn. (ppm Dry Wt.)0
Species
Organ
No.
July 3
(Late
Spring)
Betula glandulosa
Root
Stem
Leaf
6
6
6
160 ± 15
95 ± 10
145 ± 12
165 ± 15
100± 9
150 ± 8
170 ± 14
I lO'i: 10
160± 7
Ledum groenlandicum
Root
Stem
Leaf
8
8
8
120 ± 10
60± 5
63 ± 6
123±10
64± 6
67 ± 5
124 ± 11
68 ± 7
71 ± 6
a± =standard error of mean.
July 28
(Full
Summer)
August 18
(MidAutumn)
182
Nickel in Soils and Vegetation of Glaciated Terrains
species to transport metal to leaf tissue prior to litter fall provides for its removal
from the plant. Although the nickel accumulated in litter fall would be available for
recycling, levels of nickel threefold higher in leaf litter than in living leaf tissue suggest that the nickel is at least temporarily removed from the biogeochemical cycle.
It is probable that nickel forms very stable organometallic complexes that are only
slowly released (Rencz, 1979).
4.3. Examples of Effects of Glacial Dispersal on Flora
In this final section we discuss three examples of the relationship of nickel in soils
of glacial dispersal trains to nickel concentrations in and effects on vegetation.
These samples are drawn from our own work in the low arctic tundra and in the
temperate forests of the Appalachian Mountains. The details of glacial dispersal for
two of the sites, Rankin Inlet and Thetford Mines, are discussed above.
Ferguson Lake, District of Keewatin (96°50'W; 62°53'N)
The relationship between an increasing concentration of nickel in the soils and the
accumulation of the metal in leaf tissue of Betu/a glandulosa Michx., Ledum
groen/andicum Oeder., Empetrum nigrum L., and Vaccinium uliginosum L. is presented in Figure 14. In all cases low levels of plant accumulation were associated
with background soil levels of nickel. Accumulation in plants was proportional to
increasing concentrations of nickel in the soil until plants reached a threshold. The
threshold was not a well-developed plateau, and for most species there was an
abrupt decrease in metal concentration when the amount of nickel in the soil exceeded the threshold in plant tissue. Nickel in B. glandulosa Michx., for example,
decreased from a high of 153 ppm at 180 ppm soil Ni to 62 ppm at 560 ppm soil Ni
(Figure 14). It should be pointed out that many of the soil samples with high metal
levels were gossans formed postglacially on sulfide ore bodies or go5sanous muds
mixed with till by periglacial activity. Gossans typically have very low pH(< 3).
The decrease in metal concentration in plants growing at relatively high levels of
heavy metals in the soil appears to be unique. This phenomenon may be a result of
the plants growing on soil with high concentrations of heavy metals being stressed
by the toxic conditions and/or low pH (Rencz, 1979). Such plants would have lower
rates of nutrient uptake because a reduced respiratory rate would limit the amount
of energy that could be expended on uptake. It is known that uptake of nutrients
depends on the expenditure of energy and therefore any reduction in the respiratory rate would affect the plants' abilities to take up nutrients (Epstein, 1965). Reduced vigor would be atypical of other metal-tolerant plants, which appear to be
unaffected by high levels of heavy metals and in some cases have developed a need
for high concentrations of a metal (Antonovics et al., 1971). Therefore, the plants
that have survived on soils with high levels of heavy metals at Ferguson Lake may
be tolerant of heavy metals but at a reduced vigor. The reduced nickel uptake in
plants relative to the high concentrations of nickel in the soil may indicate that the
soil analyses extracted tightly bound metals. These metals would not be readily
available to plants.
N ickeJ in Vegetation of Glaciated Areas
183
Thetford Mines, Quebec
As noted earlier, the area of glacially dispersed nickel at Thetford Mines is at least
15 X 70 km. Figure 15 outlines the dispersal zone on Landsat I imagery and illustrates that regions of lighter tone are sympathetic with the ultrabasic outcrops and
the train of glacially dispersed nickel-rich ultrabasic debris. Belanger et al. (1979)
have illustrated that the tonal contrasts are a product of different vegetation types,
with each type having a characteristic reflectance level, plant species composition,
plant nickel and chlorophyll content, and associated soil nickel content. The data
suggest that nickel is one of the dominant factors in the dispersal train that affects
the vegetation patterns and illustrate that trace element "contamination" from a
natural source can affect a significant area. The effects on primary production and
F"qure 15. Landsat I image of Eastern Townships of Quebec. Heavy dashed line shows limits
of principal ultrabasic outcrops in Thetford mines area; contours are nickel concentrations
derived from Figure 6. Note contrasts in settlement and vegetation patterns between areas of
nickel-enriched soils and areas with background levels of nickel (Landsat I, image El09615068, mss band 6, June 25, 1975).
Nickel in Soils and Vegetation of Glaciated T""ains
184
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Soil Ni Concentration
Figure 16. Relationship between nickel concentrations (ppm in ash weight) in current year
leaf growth of two conifers (A. balsamea, P. marillna) and two deciduous trees (P. balsamifera,
B. papyri/era) versus nickel concentrations (total) in soil at Thetford Mines, Quebec.
organisms higher in the food chain, although under investigation, remain unknown.
The relationship between an increasing concentration of nickel in the soil and its
accumulation in tissue of Abies balsamea (L.) Mill., Picea mariana (Mill.) B.S.P.,
Populus balsamifera L., and Betula papyrifera Marsh at Thetford Mines is presented
in Figure 16. The pattern of nickel accumulation, like that at Ferguson Lake,
showed a phase where plant accumulation was proportional to soil levels, a threshold in plant accumulation, and a decrease of nickel concentrations in individuals
growing on soils with high levels of nickel. The maximal levels of accumulation
were considerably greater than "normal" levels for vegetation (Bowen, 1966).
Rankin Inlet, District of Keewatin
The town of Rankin Inlet is built over glacial sediments that are enriched in nickel.
A small sample of Salix pulchra Cham., a common arctic willow, was collected at
Rankin Inlet. It was found to accumulate nickel to high levels where growing on
soils enriched in nickel. The maximal level of 2190 ppm (dry weight) in leaf tissue
was considerably higher than other arctic species.
It is significant that, at the three study sites examined, the plants that accumu·
lated nickel to high levels are common elements of the local flora, usually the dominant species, and are common species across Canada.
References
185
S. CONCLUDING STATEMENT
Although data on nickel concentrations in North American tills and vegetation are
presently unevenly distributed about the continent, attempts are being made to
build up a data base for various types of glacial deposits and vegetation in all glaciated regions of the continent to provide, as Binzer (1974, p. 111) so aptly states,
". . . values from which the heavy-metal contamination of soils can be evaluated ..." and " ... to try to make out from what source the trace element content
in the tills was derived." One of the requirements of such a data base is that analytical results be obtained in similar ways so that regions can be compared meaning·
fully. AB an example of what such a data base might be able to show, we again refer
to Figure 1 in which are depicted histograms showing the distribution of nickel values obtained by atomic absorption techniques from the clay (0.3 µm to 2 µ) fractions of tills from selected, geologically defined regions of North America. The
histograms illustrate many of the points discussed elsewhere in this chapter, namely,
that the nickel contents of tills in each geological region differ in distinctive ways
and reflect the lithological or glacial peculiarities of the regions. The figure also confirms the high degree of natural variability in metal levels in glaciated regions and
the need for a well-defined base of natural data against which to measure man's
effect on the environment.
ACKNOWLEDGMENTS
The analytical data on which discussions in this chapter are based were derived
from samples processed through the Drift Prospecting Laboratory of Terrain Sciences Division of the Geological Survey of Canada. Most chemical analyses were
performed by Bandar.Clegg and Company, Ltd. of Ottawa using standard atomic
absorbtion techniques; some analyses were performed by Rencz in laboratories of
the Department of Biology, University of New Brunswick. Several individuals contributed samples of glacial sediments on which maps and profiles are based: A. N.
Boydell (Keewatin); B. G. Craig (Hudson Bay Lowlands); C. M. Cunningham (Keewatin); R. N. W. DiLabio (Bylot Island); A. S. Dyke (Somerset Island);J. H. Fowler
(Nova Scotia); I. M. Kettles (Illinois); B. C. McDonald (Hudson Bay Lowlands); J.
Netterville (deceased) (Somerset Island); R. G. Skinner (Hudson Bay Lowlands);
R. D. Thomas (Keewatin); and C. White (Vermont). The samples on which the
nickel profile across the Canadian Shield is based were graciously provided by the
Polar Gas Consortium through the offices of W. D. Roggensack ofE.B.A. Engineering Consultants, Ltd. of Edmonton, Alberta. R. N. W. DiLabio read an early version
of the manuscript and made numerous helpful suggestions for improving it. W. E.
Podolak compiled the histograms shown on Figure 1.
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NICKEL IN THE
ENVIRONMENT
Edited by
JEROME 0. NRIAGU
Canada Centre for Inland Waters
Burlington, Ontario, Canada
A WILEY-INTERSCIENCE PUBLICATION
JOHN WILEY & SONS
New Yolk • Chichester• Brisbane • Toronto
1980