Salinization of soil over saline-sodic overburden
from the oil sands in Alberta
Sophie Kessler1, S. Lee Barbour2, Ken C. J. van Rees3, and Bonnie S. Dobchuk1
1
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
O’Kane Consultants Inc., 2312 Arlington Ave., Saskatoon, Saskatchewan, Canada S7J 3L3
(e-mail:[email protected]); 2College of Engineering, University of Saskatchewan, 57 Campus
Dr., Saskatoon, Saskatchewan, Canada S7N 5A9; and 3College of Agriculture and Bioresources,
University of Saskatchewan, 51 Campus Dr., Saskatoon, Saskatchewan, Canada S7N 5A8.
Received 28 January 2010, accepted 20 August 2010.
Kessler, S., Barbour, S. L., van Rees, K. C. J. and Dobchuk, B. S. 2010. Salinization of soil over saline-sodic overburden
from the oil sands in Alberta. Can. J. Soil Sci. 90: 637647. Saline-sodic mine overburden (also referred to as spoil) removed
to access the oil sands in the Athabasca region of Alberta is used as backfill in open pits and is also placed in large upland
structures. These deposits are reclaimed with a soil cover to support re-vegetation. The chemistry within reconstructed soil
profiles over saline-sodic overburden was investigated to determine the nature and spatial distribution of salts in the soils.
Four reclamation treatments were compared: three layered covers (35, 50 and 100 cm thick) and one non-layered cover
(100 cm thick). Salts have accumulated in the cover soils 15 to 20 cm above the overburden, raising the electrical
conductivity in the lower part of the soil to between 4.5 and 6.0 dS m 1, which is beyond the acceptable value for
vegetation growth. Salt redistribution was not related to slope position and the pattern of salt ingress suggests that
diffusion has been the main mechanism driving salt migration into the soils during the initial 4-yr period following
placement. Cover thickness did not affect the extent of salt migration, but the overall quality of the thinner covers (35 and
50 cm) for vegetation growth was compromised by the increased salinity levels.
Key words: Saline/sodic overburden, landform salinity, soil cover salinity, salt migration, salt diffusion,
oil sands reclamation
Kessler, S., Barbour, S. L., van Rees, K. C. J. et Dobchuk, B. S. 2010. Salinisation des sols sur les morts-terrains salins-sodés
des sables bitumineux de l’Alberta. Can. J. Soil Sci. 90: 637647. Les morts-terrains salins-sodés retirer des mines de
l’Athabasca, en Alberta, pour accéder aux sables bitumineux sont employés comme remblais dans des dépotoirs à ciel
ouvert et de vastes ouvrages sur les plateaux. On restaure ces dépôts en les recouvrant de sol sur lequel la végétation pourra
pousser. Les auteurs ont étudié la chimie des profils de sol rebâtis sur les morts-terrains salins-sodés afin de déterminer la
nature et la répartition du sel dans le sol. Ils ont comparé quatre traitements de restauration: une couverture faite de
couches multiples (de 35, de 50 ou de 100 cm d’épaisseur) et une couverture d’une seule couche (de 100 cm d’épaisseur). Le
sel s’accumule dans le sol de couverture, soit 15 à 20 cm au-dessus des morts-terrains, si bien que la conductivité électrique
dans la partie inférieure du profil s’établit entre 4,5 et 6,0 dS m 1, ce qui dépasse le seuil acceptable pour la croissance de la
végétation. La redistribution du sel ne dépend pas de la pente et sa pénétration laisse croire que la diffusion est le principal
mécanisme expliquant sa migration dans le sol au cours des quatre premières années suivant les travaux. L’épaisseur de la
couverture n’affecte pas le degré de migration du sel, mais la plus forte concentration de sel dans les couvertures moins
épaisses (35 et 50 cm) empêche la croissance des plantes.
Mots clés: Morts-terrains salins-sodés, salinité du relief, salinité de la couverture de sol, migration du sel, diffusion du sel,
restauration des sables bitumineux
Oil sands mining operates under the condition that
reclaimed landscapes will have a land capability equivalent to, or better than, that which existed prior to
disturbance. Current reclamation practices involve the
capping of mine spoil with reclamation material, selectively salvaged from the original landscape, with the
characteristics required to support self-sustaining vegetation covers (Sandoval and Gould 1978).
The overburden removed to access the oil-bearing
formation at the Syncrude Canada Ltd. (SCL) Mildred
Lake Operation belongs geologically to the Clearwater
formation, which is of marine origin (Stott and Aitken
1993). The overburden is used as backfill in the open pits
Can. J. Soil Sci. (2010) 90: 637647 doi:10.4141/CJSS10019
and is also placed in large upland structures. Approximately one-third of the final reclaimed landscape at SCL
Mildred Lake operation will be underlain by such
material (Marty Yarmuch, SCL Research and Development, personal communication 2010).
Geochemical characterization (Wall 2005) has shown
that these shales are pyritic and can undergo oxidation
when exposed to atmospheric conditions, as occurs
during mining. The chemical reactions associated with
Abbreviations: SCL, Syncrude Canada Ltd.; EC, electrical
conductivity; TDS, total dissolved solids; SAR, sodium
adsorption ratio
637
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
638 CANADIAN JOURNAL OF SOIL SCIENCE
pyrite oxidation and acid sulfate weathering have been
documented (Mermut and Arshad 1986; Caruccio et al.
1988). The pyrite oxidation process generates sulfuric
acid, which reacts with carbonate minerals to release
calcium ions, which then exchange with sodium ions
bound to the shale. This results in a pore-water
chemistry that is saline-sodic at levels that are adverse
to plant growth, with measured electrical conductivity
(EC) levels as high as 17 dS m 1 and sodium adsorption
ratio [SAR Na/â(CaMg)/2, with cation concentrations in mmolc L1] levels of 35 or more.
When the study area was constructed, Syncrude’s
operating approvals required the placement of a 100cm-thick cover when reclaiming saline-sodic overburden
(Marty Yarmuch, SCL Research and Development,
personal communication 2009). Selective salvaging
during mining, stockpiling, and handling of reclamation
material represents a major cost for reclamation; hence,
there is an economic incentive to evaluate the performance of thinner covers.
Several research projects have investigated the effectiveness of different subsoil-topsoil depths to reclaim
mined lands (Schuman and Power 1981; Barth and
Martin 1984; Hargis and Redente 1984). Most studies
have evaluated cover performance and reclamation
success in terms of crop yield, arguably because they
have been completed in the Northern Great Plains coal
mining region where the major end land uses are
agriculture and rangeland (Power et al. 1981; Merrill
et al. 1985; Schuman et al. 1985; Oddie and Bailey 1988).
A discrete subsoil-topsoil layer system was usually
found to give better crop response than a uniform cover
layer consisting of a mixture of mineral and organic
matters (McSweeney et al. 1981) and, overall, crop yield
seemed to benefit from greater capping depths (McGinnies and Nicholas 1980; Sydnor and Redente 2000),
though there has been little consensus on preferred
subsoil-topsoil thicknesses. This lack of consensus might
be due to the diversity of reclamation prescriptions in
these studies as well as differing characteristics of
underlying mine spoil, climatic conditions, end landuse goals, and the short duration of the studies (Hargis
and Redente 1984).
A few studies have focused on the changes in the
chemistry of the reclamation soil following placement
over saline-sodic mine overburden. Generally, an increase in soluble salts in the cover material immediately
over the spoil has been observed. The increase has been
attributed to upward salt movement driven by diffusion
due to the sharp salinity gradient between the spoil and
overlying soil, advective transport due to upward water
movement in response to evapotranspiration, and the
restriction to downward flushing created by the presence
of the underlying low hydraulic conductivity salinesodic material (Sandoval and Gould 1978; Dollhopf
et al. 1980; Merrill et al. 1983; Oddie and Bailey 1988;
Bailey 2001). More recently, researchers have looked at
reclamation success with time and have emphasized the
need to study the evolution of the physical and chemical
properties of reconstructed soils in order to project the
success of reclamation in the future (Potter et al. 1988;
Bailey 2001; Schladweiler et al. 2004; Bowen et al. 2005).
This is especially important in the Athabasca basin,
where the dominant land use is forestry, and where
reclamation success cannot be assessed during the span
of a few years, as for annual crops.
The objectives of this study were: (1) to characterize
the short term (4 yr) evolution of salinity profiles in
the reclaimed soil covers placed over saline-sodic overburden; (2) to evaluate the influence of cover thickness
and slope position on the salt redistribution in the
reclaimed material; and (3) to identify the dominant
mechanism of salt transport responsible for these
profiles.
MATERIALS AND METHODS
Site Description
The study site was on Syncrude Canada Limited (SCL)
Lease #17 within the SCL Mildred Lake operation in the
Athabasca Oil Sands region approximately 40 km north
of Fort McMurray, AB. An experimental watershed
consisting of three different depths of reclamation soil
covers was constructed in 1999 on a re-contoured salinesodic overburden pile, identified as South Bison Hills.
The soil covers were laid out as three adjacent 1-ha strips,
200 m long and 50 m wide. The strips are on a northfacing, approximately 5:1 (horizontal: vertical) slope
oriented lengthwise in an approximate south-north
direction.
The reclamation prescriptions for the soil covers are
designed to mimic the natural formation of a topsoil
organic/mineral surface topsoil mix (LFH/A horizons)
and a mineral B subsoil horizon by utilizing two layers
of material. The subsoil is composed of salvaged glacial
soils, while the surface horizon is a mixture of glacial
soils mixed with peat. The soil prescriptions are (from
west to east): 30 cm of subsoil topped by 20 cm of peat/
glacial soil mixture; 20 cm subsoil with 15 cm topsoil;
and 80 cm subsoil with 20 cm topsoil. The resulting
total soil cover thicknesses were 50, 35, and 100 cm,
respectively.
An older 3-ha cover study area was also constructed
at South Bison Hills in 1996. A naturally occurring
wetland developed at this location and the wetland and
the upslope reclamation area surrounding it are commonly referred to as Bill’s Lake. This study site is
located approximately 500 m from the three soil cover
test plots. The prescription for the Bill’s Lake site is a
single layer of material, nominally 100 cm thick. The
cover material consists of a single mixture of peat/glacial
mineral soil. Instrumentation to monitor the hydrology
of these sites was installed in 1999 (Stolte et al. 2000).
The north-facing hillside upslope of the wetland at Bill’s
Lake was selected for comparison with the three soil
covers (Fig. 1).
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
KESSLER ET AL. * SALINIZATION OF SOILS OVER OIL SAND SPOIL
Fig. 1. Soil cover depth treatments on a re-contoured salinesodic waste pile.
The reclamation soils for all of the sites had been
selectively salvaged from the same lease area before
mining and were stockpiled until placement. Following
layout of the cover material in early 1999, the reclaimed
area was seeded with a barley (Hordeum vulgare)
cultivar to prevent erosion of the topsoil and, later in
the year, was planted with aspen (Populus tremuloides
Michx.) and white spruce [Picea glauca (Moench) Voss]
seedlings.
This study was part of an ongoing instrumented
watershed research project to evaluate the success of
reconstructed watersheds and to identify the mechanisms controlling water and salt migration in these
landforms with time (Barbour et al. 2004). As part of
other collaborative studies (data not presented here),
water tables were monitored with piezometers to
characterize the deep hydrogeology of the South Bison
Hills (Chapman 2008), meteorological data were measured with an automated meteorological system, and
soil water content and suction were measured using
automated profiles of time domain reflectometry and
thermal conductivity sensors (Boese 2003).
Soil Sampling
Soil profiles at more than 40 locations were sampled in
June 2002. The sampling scheme consisted of one linear
transect per soil cover, oriented along the central slope
of the cover. At the Bill’s Lake site, the sampling
transect was laid out following a ‘‘Z’’ pattern covering
both north- and east-facing slopes. Soil samples were
collected along depth profiles at each of the 10 locations
spaced at regular intervals (approximately every 20 m).
Each profile was sampled in approximately 10-cm
depth increments using a Dutch auger. Due to site
restrictions, only manual sampling methods were used.
To ensure that samples were obtained above and below
the interface, the first (surface) sample increments for
the 100-cm and 50-cm cover depths were 5 cm, followed
by 10-cm samples through the remainder of the profile.
All soil profiles were sampled to a depth of 50 cm below
the interface. The boundaries between the different
639
material types were respected as closely as allowed by
the sampling method. Each material type was a distinctly different color, which aided in discriminating
between the material types. Three cores were extracted
in close proximity to each other at each sampling site so
that each sample was a composite of three samples from
the same depth.
In addition, eight samples from selectively salvaged
glacial mineral soil were obtained from SCL in 2003
as a reference for background conditions. The glacial
mineral soil was stripped off the surface prior to mining
and was stockpiled prior to construction of the reclamation covers on South Bison Hill. The reference sample
was used to compare the ranges of cover soil chemistry
within the mineral soil stockpile with those same
materials in the cover.
Laboratory Analysis
Immediately after collection of soil samples, sub-samples
were taken for gravimetric water content determination.
Volumetric water contents were estimated from the
gravimetric water contents based on dry bulk density
measurements of the placed cover materials in 2001
(Table 1). The remainder of each sample was air-dried
and ground to pass through a 2-mm sieve. Saturated
pastes were prepared and soil pH was determined on
the paste (McKeague 1978). Saturation extracts were
obtained on all the samples by vacuum filtration and
electrical conductivity (EC) and major soluble ions were
determined on the extracts (McKeague 1978). Cation
concentrations (calcium, magnesium, potassium,
sodium) were measured by atomic absorption/flame
emission spectrophotometry (Varian Spectra AA, Varian Inc., Palo Alto, CA); sulfate was measured by
automated turbidimetry (Technicon autoanalyzer, Technicon Industrial Systems, Tarrytown, NY); chloride and
nitrate by colorimetry (Technicon autoanalyzer, Technicon Industrial Systems, Tarrytown, NY); and carbonate/
bicarbonate by titration with 0.1 M HCl (Auto-titrator
Metrohm, Metrohm AG, Herisau, Switzerland).
Data Analysis
Mean values of total dissolved solids (TDS) and SAR
determined for each reclamation prescription (cover
thickness) were compared with Dunnett’s C pair-wise
multiple comparison allowing for unequal variances.
Table 1. Bulk density measurements of the South Bison Hills materials
Boese (2003)
Bulk density (g cm 3)
Material
Min
Max
Mean
SDz
Peat/glacial topsoil
Glacial subsoil
Overburden
0.20
0.93
0.98
1.40
1.64
1.74
0.92
1.28
1.47
0.31
0.21
0.20
z
Standard deviation.
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
640 CANADIAN JOURNAL OF SOIL SCIENCE
Square-root transformation of the data was found to
reduce the coefficient of variation but the transformation compromised the normality of the distribution.
Therefore, the tests were performed on the data without
the square-root transformation.
The effect of reclamation prescription (cover thickness) on salinity-sodicity was assessed in two steps. In
the first step, the comparison was done on a whole cover
basis with the salinity values from all samples averaged
per material type (i.e., cover versus overburden) and per
reclamation prescription (i.e., cover thickness) without
consideration of sample depth. The total depth of cover
was evaluated rather than the individual material type to
determine the quality of the entire cover as a growing
medium. Spatial variations in the thickness of the peat/
glacial subsoil also made a material-specific comparison
difficult.
In the second step, the comparison was based on
samples taken from each of the three layers above the
cover/overburden interface and one layer below the
interface. Salinity values were averaged per depth
increment for all sampling locations in the same cover.
Because the transition in soil chemistry across the
interface between the spoil and the cover was of greatest
interest, the soil profiles were defined with reference to
the interface, which is represented as the origin on the
depth axis. Differences in TDS and SAR were compared
for the four layers (010 cm, 1020 cm and 2030 cm
above the interface and 010 cm below interface) for
each cover prescription. Mean TDS and SAR values for
consecutive layers among the cover prescriptions were
compared by paired t-tests (P 0.05).
To compare the results of the sampling based on
slope, the salinity and the water content values were
averaged for the top three sampling profiles to represent
upper slope, the middle four sampling profiles to
represent mid-slope, and the bottom three sampling
profiles to represent lower slope conditions.
Modeling
To illustrate a typical range of profiles for diffusiondriven upward migration of salts into the cover system,
a simple one-dimensional finite-difference model was
developed. The model assumed Fickian diffusion, as
shown in Fick’s First and Second Laws (Eqs. 1 and 2):
qDe
@C
@t
@C
@x
De @C
neq @x2
De
D0
0:3b
u
0:45u
n
(3)
where u is volumetric water content (volume/volume),
D0 is solute free-water diffusion coefficient (area/time)
10
m2 s 1 from
[modeling used D0 (SO2
4 , 0C) 5 10
Li and Gregory (1974)], n is porosity (volume/volume),
and b is negative slope of the water retention curve in loglog coordinate system (Campbell 1974).
The Zill and Cullen (1992) relationship was used to
predict the stability of the model based on the nodal
spacing (Dx), the diffusion coefficient (De) and the
timestep (Dt) (Eq. 4):
De Dt
0:5
Dx2
(4)
The nodal spacing was constant with depth, and the
timestep did not vary. Water content, and therefore
diffusion coefficient, varied with depth but not with
time. For simplicity, the model assumed that the
equivalent porosity (neq) was equal to the total porosity
(n). Based on the water retention curves of the materials
[Boese (2003) data not shown], b was determined to be
10 for both the overburden and the glacial subsoil. No
water retention data were available for the peat material. A sensitivity analysis of the b value in the peat
revealed little sensitivity due to the limited salt transport
in the peat during the modeled timeframe; therefore, 10
was also used as the b value for the peat.
The numerical diffusion models were run based on
an initial concentration profile in the overburden of
C/C0 1 and C/C0 0 in the cover material, where C0
defines the source concentration in the overburden
below the interface. The model was run for a duration
from cover placement to soil sampling, an elapsed time
of approximately 40 mo. The water content profiles used
in the modeling were taken from the volumetric water
contents shown in Fig. 3. However, to simplify the
modeling, a single value of volumetric water content was
used for each material layer based on the average
volumetric water content calculated within each material type. Three different water content profiles were
used for each of the cover treatments based on the
minimum, average, and maximum volumetric water
contents as calculated using the minimum, average,
and maximum bulk density (Table 1).
(1)
RESULTS AND DISCUSSION
(2)
where q is diffusive mass flux (mass/area/time), De is
bulk soil diffusion coefficient (area/time), C is concentration of solute (mass/volume), x is depth (length), and
neq is equivalent porosity (volume/volume).
The bulk diffusion coefficient (De) was estimated using
the method of Olesen et al. (1996) as described by Eq. 3:
Salinity Profiles
Analysis of the saturation extracts of the cover and
overburden samples (data not shown) showed that
sulfate was the dominant anion in the soil system
(evaluated based on the combined test results from
both the cover and overburden), accounting for 94% of
the total anion content. Bicarbonate (4%) and chloride
(2%) made up the remaining anions, with a negligible
contribution of nitrate. The cation distribution was
KESSLER ET AL. * SALINIZATION OF SOILS OVER OIL SAND SPOIL
dominated by sodium, which made up 71% of the cation
content. Calcium, magnesium and potassium represented 14, 12 and 3%, respectively.
The salinity profiles for the three reclamation prescriptions showed a common pattern (Fig. 2), including
a strong increase in salinity with depth to the greatest
EC (dS m-1)
(a)
100
0
5
TDS (g kg-1)
SAR
10
15
0
10
20
30
Distance from Interface (cm)
D3
60
60
40
-40
-40
-40
-60
-60
TDS (g kg-1)
SAR
10
0
15
10
20
30
100
D1
D2
D3
80
D2
D3
60
60
40
Overburden
-20
-40
-40
-40
-60
-60
-60
EC (dS m-1)
TDS (g kg-1)
SAR
0
10
20
30
100
D1
D2
80
D3
60
60
40
20
D1
D2
D3
0
10
D1
80
D2
D3
40
20
Subsoil
Subsoil
0
Overburden
Overburden
Overburden
5
60
20
Subsoil
0
100
40
0
Subsoil
0
-20
80
D3
Overburden
-20
100
D2
20
Subsoil
0
15
8
40
Overburden
10
6
D1
20
5
4
60
Subsoil
0
2
80
40
20
0
100
D1
Distance from Interface (cm)
Overburden
-20
0
Subsoil
0
-20
5
D3
Overburden
-20
0
D2
20
Subsoil
0
80
(c)
D1
20
Overburden
100
15
40
Subsoil
0
10
80
40
20
5
60
EC (dS m-1)
Distance from Interface (cm)
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
D1
D2
D3
80
D2
0
100
D1
(b)
40
100
80
641
-20
-20
-20
-40
-40
-40
-60
-60
-60
Fig. 2. Mean electrical conductivity (EC), sodium adsorption ratio (SAR), and total dissolved solids (TDS) for the 50-cm (D1),
35-cm (D2), and 100-cm (D3) soil cover depth treatments in the (a) upper, (b) mid, and (c) lower slope positions at South Bison Hills
in 2002.
in deeper layers (Barbour et al. 2004; Elshorbagy and
Barbour 2007).
value in the overburden. Comparable patterns have been
reported in studies of soluble salt movements for both
mature, natural landscapes (Heck and Mermut 1992;
Miller and Pawluk 1994) and reconstructed soil systems
(Sandoval and Gould 1978; Merrill et al. 1980; Barth
and Martin 1984; Bailey 2001). All studies concluded
that the cause was the upward movement of salts,
although they disagreed on the source (lower soil layers
or saline groundwater) and on the main process driving
this upward transport.
Regardless of the reclamation prescription, no distinct
trend in either salinity (TDS) or sodicity (SAR) levels
was associated with slope position. Salinity and sodicity
were evaluated by plotting the results from the transect
sampling versus the location of the sampling point on
the slope. Zones of high and low levels in the cover
(subsoil and topsoil) seemed to be randomly distributed
along each transect (i.e. along the slope). Salinity and
sodicity values in the cover were generally related to the
salinity and sodicity of the underlying overburden. This
suggests that salt movement at this stage was mainly
one-dimensional.
The volumetric water content profile of each prototype cover calculated using each of the minimum,
maximum, and average bulk density values illustrates
the range in volumetric water content present at
sampling (Fig. 3). The greater range in bulk density in
the peat results in greater uncertainty in the volumetric
water content in this layer compared with the subsoil
and the overburden.
Water content varied more with depth in the peat
material, with less variation with depth in the subsoil
and overburden layers. The deeper covers show less
variation in water content with depth in the subsoil. Five
years of water content monitoring at these sites (data
not shown) found greater variation in water content in
shallow layers and cover prescriptions and less variation
0
20
40
60
80
Salinity Sodicity and Cover Thickness
Cover SalinitySodicity
When compared among cover types, mean TDS values
of each cover were significantly greater in the cover soils
compared with the stockpiled material (Table 2). Mean
TDS values were not significantly different between the
35- and 50-cm covers, or between the layered and nonlayered 100-cm covers although the average salinity of
the two thinner covers was significantly greater than the
100-cm covers.
Similarly, mean SAR values for the cover soil were
significantly greater than the stockpiled soil material.
Mean SAR values for the 50-cm and the two 100-cm
covers were not significantly different, but the mean
SAR value for the 35-cm cover was significantly greater
than the other cover types (Table 2).
The increase in mean salinity in the reconstructed soils
was consistent with other findings. Sandoval and Gould
(1978) argued that the initial quality of the reclamation
material would unavoidably suffer some deterioration
with time once it was placed over saline-sodic spoil,
and that this deterioration was to be accounted for in
the choice of a reclamation prescription, so that the
overall capability of the reclaimed cover would not be
compromised. Doll et al. (1984) found that soil-forming
processes would initiate changes as soon as the material
was placed, and Barth and Martin (1984) reported
significant increases in sodium concentrations in reconstructed soil units within 4 yr after placement. The rate
of change diminished in subsequent years, with reports
of very limited additional changes past one or two
decades (Bailey 2001).
Soil salinity is harmful to plants because of the
osmotic and toxic effects of the salts on plant physiology.
0
100
20
40
60
80
100
140
140
D1 MAX
D1 AVG
100
0
120
100
D2 MAX
D2 AVG
120
100
80
80
60
60
60
40
Peat
40
60
80
100
D3 MIN
80
40
20
140
D2 MIN
D1 MIN
120
Volumetric Water Content (%)
Volumetric Water Content (%)
Volumetric Water Content (%)
Distance from Interface (cm)
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
642 CANADIAN JOURNAL OF SOIL SCIENCE
D3 MAX
D3 AVG
Peat
40
Peat
20
20
0
Glacial Subsoil
0
-20
-20
-60
(a)
0
Overburden
Overburden
-40
20
Glacial Subsoil
-40
-60
Glacial Subsoil
Overburden
-20
(b)
-40
(c)
-60
Fig. 3. Volumetric water content for the 50-cm (D1), 35-cm (D2), and 100-cm (D3) soil cover depth treatments (midslope) at South
Bison Hills in 2002 using the minimum, mean, and maximum bulk density.
KESSLER ET AL. * SALINIZATION OF SOILS OVER OIL SAND SPOIL
values remained well below the threshold value of 13,
which defines sodic soils (Sumner et al. 1998). Reclamation prescription (cover depth) appeared to have a
limited effect on mean sodicity levels. Little to no
correlation between cover thickness and SAR has also
been reported in previous studies (Bailey 2001). Given
that the average SAR values were less than 6, it appears
that all the reclamation prescriptions were within an
acceptable range.
The limited TDS and SAR differences among reclamation prescriptions were consistent with results reported in
previous studies. Bailey (2001) found no difference
in overall salinity and sodicity between two 70- and
110-cm-thick covers. Schladweiler et al. (2004) also
reported that reclamation prescription had no overall
effect on the soil chemical properties of three 15-, 30-, and
56-cm thick covers.
Table 2. Mean total dissolved solids (TDS) and sodium adsorption ratio
(SAR) values for the soil cover depth treatments
Reclamation prescription
TDS (g kg1)
SAR [(mmolc L 1)1/2]
D1 (50 cm)
D2 (35 cm)
D3 (100 cm)
Bill’s Lake
(100 cm non-layered)
Stockpiled glacial subsoil
1.20a
1.57a
0.66b
0.66b
4.21ab
5.23a
2.61b
2.43b
0.26c
1.39c
ac Means within a column followed by the same letter are not
significantly different (PB0.05).
Several studies have concluded that plant response was
affected by the mean salinity in the root zone, regardless
of the soil salinity distribution patterns (Shalhevet and
Bernstein 1968; Shalhevet et al. 1969; Maas and
Hoffman 1977). Salinity effects are often species specific.
The commonly accepted salinity scale (Tanji 1990)
defines optimum conditions with an electrical conductivity (EC) range of 0 to 2 dS m 1. The 2 to 4 dS m 1 EC
range represents a marginally acceptable range, where
some limitations to the growth of sensitive plants will
become noticeable. Both 100-cm covers had mean
salinities corresponding to EC values of approximately
1.5 dS m 1, representing adequate growing conditions,
while the 50- and 35-cm covers had mean salinities of 2.2
and 2.9 dS m 1, respectively, which could be limiting to
plant growth. Salt effects to white spruce have been
reported at EC levels0.5 dS m 1 (Maynard et al. 1997;
Staples and Van Rees 2001).
Sodicity levels in the reclaimed material also increased
significantly after reclamation (Table 2); however, SAR
SalinitySodicity at the Transition Zone
The zone spanning the interface between soil cover
and overburden has been shown to be the most dynamic
in terms of soil chemistry within reconstructed profiles
(Sandoval and Gould 1978; Merrill et al. 1983; Bailey
2001). Salinity levels decreased exponentially with
distance (elevation) above the interface, as shown by
the significant differences in TDS values between consecutive elevation increments (Fig. 4). The rate of
decrease tapered off 20 to 30 cm above the interface
for all covers except the 100-cm layered cover, and the
differences in average TDS values between elevations of
10 to 20 cm and 20 to 30 cm above the interface were not
significant. There was no significant effect of reclamation prescription on the shape of this salinity gradient.
TDS (g kg-1)
0
Elevation Increment above Interface (cm)
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
643
+(20-30)
1
2
3
4
5
6
7
8
a
ab
9
35 cm
50 cm
b
ab
100 cm
Bill's Lake
a
+(10-20)
a
a
a
a
a
+(0-10)
a
a
Glacial Subsoil
a
a
a
-(0-10)
a
Overburden
Fig. 4. Mean total dissolved solids (TDS) for the soil cover depth treatments in the transition zone between overburden and subsoil.
Whiskers represent one standard deviation. Means within each elevation increment followed by a similar lowercase letter are not
significantly different (P B0.05).
Within each elevation increment, there were no major
differences in TDS among the four reclamation prescriptions (Fig. 4).
The decreasing SAR values with increasing distance
(elevation) above the interface (Fig. 5) followed the
same trends as TDS values. The rate of decrease,
however, was maintained into the 20- to 30-cm elevation
increment for all reclamation prescriptions, with significant SAR differences between the two upper increments (10 to 20 cm and 20 to 30 cm) for all covers
(Fig. 5). As observed for TDS (Fig. 4), the reclamation
prescription appeared to have no effect on the shape
of the sodicity gradient, with no major differences in
SAR among the different covers within each elevation
increment (Fig. 5).
Patterns of salinity distribution in the transition zone
indicate that there has been an upward movement of
salts from the overburden into the covers. Considerable
increases in salinity and sodicity occurred in the zone
0 to 10 cm above the interface, with smaller increases
shown in the zone approximately 10 to 20 cm above the
interface. Both the shape and the thickness of the
affected zone were consistent with the 15- to 20-cm
zone above the subsoil reported in previous studies on
reconstructed soils over saline-sodic overburden (Merrill
et al. 1980; Barth and Martin 1984; Bailey 2001). Merrill
et al. (1980, 1983) showed with both field and laboratory
experiments that accumulation of salts at the base of
covers over saline-sodic overburden could be attributed
to diffusion processes driven by the concentration
gradient between overburden and cover, and facilitated
by the low hydraulic conductivity of the underlying
sodic overburden that limited downward leaching of
the salts.
Ion diffusion into the cover affected the cation
balance, thus significantly increasing the SAR in the
lower 20 cm of the covers. However, SAR did not reach
the critical levels of 13, even in the layer immediately
above the interface. On their own, high SAR values are
typically associated with structural degradation of soils,
clay dispersion and low hydraulic conductivity, all of
which are deleterious to root growth. Several researchers
(Quirk and Schofield 1955; Sumner et al. 1998; Quirk
2001), however, state that there are mitigating effects of
ionic concentrations in soil solution on sodicity-induced
soil degradation due to suppression of the electric
double layer. Under the current combination of moderate SAR and elevated EC conditions, the integrity of the
reconstructed covers does not seem at risk and no major
signs of degradation in soil structure, such as swelling or
slaking-induced slope failures or erosion, were observed
in the critical zone.
The extent of salt ingression at the base of the subsoil
was not affected by the thickness of the cover. Bailey
(2001) made similar observations, and concluded that
the process driving salt transport must be similar within
comparable environments. On the basis of their modeling exercise, however, Merrill et al. (1983) predicted
further ingress of salts into the subsoil with greater cover
thickness. Our data do not support their prediction of
greater ingress with thicker covers.
Salt Diffusion
Bulk soil diffusion coefficients (De) estimated for
each material varied from 1.1 1014 to 1.4 1010
m2 s 1 for the peat/glacial topsoil, from 5.3 10 12
to 9.0 1011 m2 s 1 for the glacial subsoil, and from
5.0 1012 to 6.5 1011 m2 s1 for the overburden.
SAR
0
5
10
15
20
25
a
Elevation Increment above Interface (cm)
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
644 CANADIAN JOURNAL OF SOIL SCIENCE
+(20-30)
35 cm
a
a
50 cm
a
100 cm
Bill's Lake
a
a
+(10-20)
a
a
a
a
+(0-10)
ab
Glacial Subsoil
b
a
ab
a
-(0-10)
b
Overburden
Fig. 5. Mean sodium adsorption ratio (SAR) for the soil cover depth treatments in the transition zone between overburden and
subsoil. Whiskers represent one standard deviation. Means within each elevation increment followed by a similar lowercase letter are
not significantly different (PB 0.05).
KESSLER ET AL. * SALINIZATION OF SOILS OVER OIL SAND SPOIL
C/C0
0.0
0.2
0.4
0.6
C/C0
0.8
1.0
D1 Min WC
120
Distance from Interface (cm)
0.0
0.2
0.4
0.6
C/C0
0.8
1.0
140
140
D1 Max WC
1.2
0.0
D2 Min WC
120
D2 Avg WC
100
D2 Max WC
0.6
0.8
1.0
1.2
80
60
60
60
40
D3 Min WC
D3 Avg WC
100
80
Peat
0.4
120
80
40
0.2
140
D1 Avg WC
100
D3 Max WC
Peat
40
Peat
20
Glacial Subsoil
-20
-60
20
20
Glacial Subsoil
0
0
-40
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
1.2
645
Overburden
(a)
-20
Overburden
-40
-60
Glacial Subsoil
0
-20
Overburden
-40
(b)
-60
(c)
Fig. 6. Concentration profiles for the 50-cm (D1), 35-cm (D2), and 100-cm (D3) soil cover depth treatments from diffusion modeling
using simplified volumetric water content (WC) profiles based on minimum, mean, and maximum volumetric water content and
diffusion coefficients estimated from material properties.
Concentration profiles from the numerical modeling
were similar among the three covers (Fig. 6), which
agrees with the measured data that showed no correlation in salinity or sodicity with cover treatment. Differences in the concentration profiles represent the range of
water content variation estimated from bulk density
measurements. This illustrates the sensitivity of the
modeling to the water content of the material (due to
the increase in the effective diffusion coefficient with
higher water content). The shape of the predicted profiles
is similar to those in Fig. 2, where the profiles are roughly
symmetrical about the interface and have a sigmoidal
shape with background concentrations (C/C0 0)
reached at 20 to 40 cm above the overburden. Increased
downslope water movement in the form of surface runoff
and subsequent infiltration as well as interflow along the
cover/overburden interface (Kelln 2009) may lead to salt
redistribution along the slope.
CONCLUSIONS
Within a few years of placement for all soil cover depths,
a significant increase in salinity (as measured by TDS)
was observed at the base of the cover above the spoil
interface compared with salinity in stockpiled material.
The extent of salt ingress was not related to cover
thickness, with all soil cover depths exhibiting a similar
increase in salts about 20 cm above the interface with the
spoil. Average salinity in the thinner soil covers was
significantly greater than salinity in the 100-cm covers,
thus slightly decreasing the overall capability of the 35and 50-cm covers for vegetation growth. The thicker soil
covers, D3 and Bill’s Lake, remained within the optimal
salinity range for vegetation growth. Sodicity also
increased significantly at the interface with the spoil in
all cover treatments compared with SAR values of nonplaced material, regardless of the cover thickness. The
SAR levels were not significantly different among the
covers, and a similar increase in sodicity was observed at
the base of all covers, regardless of thickness. In spite of
their increase, SAR levels remained within acceptable
limits and no adverse effects on soil structure were
observed in these soils. Spatial variation in the salinity
or sodicity of the covers was not related to slope
position. The thicker covers performed better as a
reclamation prescription and have sufficient water
storage capacity above the salt-affected zone to maintain vegetation communities.
The shape and depth of the salinity profile suggests
that the transport process was predominately diffusion.
A finite-difference diffusion model was used to generate
hypothetical concentration profiles based on the material characteristics and time-frame of the three soil cover
treatments since placement. The modeled profiles have a
similar shape and depth compared with the observed
profiles, indicating that the transport process was
dominated by diffusion during the early period after
placement. Given the high concentration gradients
between the overburden and the glacial subsoil, diffusion likely dominated the transport during the early
period following placement. As the gradient decreases
and the landscape matures with time, other transport
processes may become more apparent.
Bailey, D. L. H. 2001. Properties of soil profiles over sodic
mine spoil 16 years after construction. M.Sc. thesis, University
of Alberta, Edmonton, AB.
Barbour, S. L., Chapman, D., Qualizza, Q., Kessler, S., Boese,
C., Shurniak, R., Meiers, G., O’Kane, M., Hendry, J. and
Wall, S. 2004. Tracking the evolution of reclaimed landscapes
through the use of instrumented watersheds A brief history
of the Syncrude Southwest 30 overburden reclamation
research program. In Proceedings of the International Instrumented Watershed Symposium, Edmonton, AB, Jun. 2225.
Barth, R. C. and Martin, B. K. 1984. Soil depth requirements
for revegetation of surface-mined areas in Wyoming, Montana
and North Dakota. J. Environ. Qual. 13: 399404.
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
646 CANADIAN JOURNAL OF SOIL SCIENCE
Boese, C. D. 2003. Design and installation of a field
instrumentation program for the evaluation of soil-atmosphere
water fluxes in a vegetated cover over saline/sodic shale
overburden. M.Sc. thesis, University of Saskatchewan,
Saskatoon, SK.
Bowen, C. K., Schuman, G. E. and Olsen, R. A. 2005. Influence
of topsoil depth on plant and soil attributes of 24-year old
reclaimed mined lands. Arid Land Res. Manage. 19: 267284.
Campbell, G. S. 1974. A simple method for determining
unsaturated conductivity from moisture retention data. Soil
Sci. 117: 311314.
Caruccio, F. T., Hossner, L. R. and Geidel, G. 1988.
Pyritic materials: Acid drainage, soil acidity and liming. Pages
159190 in L. R. Hossner, ed. Reclamation of surface-mined
lands. CRC Press, Boca Raton, FL.
Chapman, D. E. 2008. Hydrogeologic characterization of a
newly constructed saline-sodic clay overburden hill. M.Sc.
Thesis, University of Saskatchewan, Saskatoon, SK.
Doll, E. C., Merrill, S. D. and Halvorson, G. A. 1984. Soil
replacement for reclamation of stripmined lands in North
Dakota. Agric. Exp. Stn, North Dakota State University,
Fargo, ND. Bull. 514.
Dollhopf, D. J., Depuit, E. J. and Klages M. G. 1980. Chemical
amendment and irrigation effects on sodium migration and
vegetation characteristics in sodic minesoils in Montana. Bull.
736. Agric. Exp. Stn, Montana State University, Bozeman,
MT.
Elshorbagy, A. and Barbour, S. L. 2007. Probabilistic approach
for design and hydrologic performance assessment of reconstructed watersheds. J. Geotech. Geoenviron. Eng. 133:
10901118.
Hargis, N. E. and Redente, E. F. 1984. Soil handling for surface
mine reclamation. J. Soil Water Conserv. 39: 300305.
Heck, R. J. and Mermut, A. R. 1992. Genesis of Natriborolls
(Solonetzic) in a closed lake basin in Saskatchewan, Canada.
Soil Sci. Soc. Am. J. 56: 842848.
Kelln, C. J., Barbour, S. L. and Qualizza, C. 2009. Fracturedominated subsurface flow and transport in a sloping reclamation cover. Vadose Zone J. 8: 96107.
Kessler, S. P. 2007. Salinity profiles in reconstructed soils over
saline-sodic waste from the oil sands industry. M.Sc. thesis,
University of Saskatchewan, Saskatoon, SK.
Li, Y.-H. and Gregory, S. 1974. Diffusion of ions in sea water
and deep-sea sediments. Geochim. Cosmochim. Acta 38:
703714.
Maas, E. V. and Hoffman, G. J. 1977. Crop salt tolerance Current assessment. J. Irrig. Drain. Div. Am. Soc. Civ. Eng.
103: 115134.
Maynard, D. G., Mallett, K. I. and Myrholm, C. L. 1997.
Sodium carbonate inhibits emergence and growth of
greenhouse-grown white spruce. Can. J. Soil Sci. 77: 99105.
McGinnies, W. J. and Nicholas, P. J. 1980. Effects of topsoil
thickness and nitrogen fertilizer on the revegetation of coal
mine spoils. J. Environ. Qual. 9: 681685.
McKeague, J. A. (ed.). 1978. Manual on soil sampling and
methods of analysis. 2nd ed. Canadian Society of Soil Science,
Ottawa, ON.
McSweeney, I., Jansen, J. and Dancer, W. S. 1981. Subsurface
horizon blending: an alternative strategy to B horizon replacement for the construction of post-mine soils. Soil Sci. Soc.
Am. J. 45: 794799.
Mermut, A. R. and Arshad, M. A. 1986. Significance of sulfide
oxidation in soil salinization in Saskatchewan. Pages 266268
in G. Van der Kamp and M. Maunicky, eds. Proc.
Can. Hydrogeological Conf., 3rd, Saskatoon, SK. 1986 Apr.
2023. Int. Assoc. Hydrogeologists, Can. Natl. Chapter,
Saskatoon, SK.
Merrill, S. D., Doering, E. J. and Power, J. F. 1980. Changes of
sodicity and salinity in soils reconstructed on strip-mined
lands. N. D. Farm Res. 37: 1316.
Merrill, S. D., Doering, E. J., Power, J. F. and Sandoval, F. M.
1983. Sodium movement in soil-minespoil profiles: Diffusion
and convection. Soil Sci. 136: 308316.
Merrill, S. D., Smith, S. J. and Power, J. F. 1985. Effect of
disturbed soil thickness on soil water use and movement under
perennial grass. Soil Sci. Soc. Am. J. 49: 196202.
Miller, J. J. and Pawluk, S. 1994. Genesis of Solonetzic soil as
a function of topography and seasonal dynamics. Can. J. Soil
Sci. 74: 207217.
Oddie, T. A. and Bailey, A. W. 1988. Subsoil thickness effects
on yield and soil water when reclaiming sodic minespoil.
J. Environ. Qual. 17: 623627.
Olesen, T., Moldrup, P., Henriksen, K. and Petersen, L. W.
1996. Modeling diffusion and reaction in soils: IV.
New models for predicting ion diffusivity. Soil Sci. 161:
633645.
Potter, K. N., Carter, F. S. and Doll, E. C. 1988. Physical
properties of constructed and undisturbed soils. Soil Sci. Soc.
Am. J. 52: 14531438.
Power, J. F., Sandoval, F. M., Ries, R. E. and Merrill, S. D.
1981. Effects of topsoil and subsoil thickness on soil water
content and crop production on a disturbed soil. Soil Sci. Soc.
Am. J. 45: 124129.
Quirk, J. P. 2001. The significance of the threshold and
turbidity concentrations in relation to turbidity and microstructure. Aust. J. Soil Res. 39: 11851217.
Quirk, J. P. and Schofield, R. K. 1955. The effect of electrolyte
concentration on soil permeability. J. Soil Sci. 6: 163178.
Sandoval, F. M. and Gould, W. L. 1978. Improvement of
saline- and sodium-affected disturbed lands. Pages 485504 in
F. W. Schaller and P. Sutton, eds. Reclamation of drastically
disturbed lands. ASA, Madison, WI.
Schladweiler, B. K., Vance, G. F., Legg, D. E., Munn, L. C. and
Haroian, R. 2004. Influence of variable topsoil replacement
depths on soil chemical parameters within a coal mine in
Northeastern Wyoming, USA. Arid Land Res. Manage. 18:
347358.
Schuman, G. E. and Power, J. F. 1981. Topsoil management on
mined lands. J. Soil Water Conserv. 36: 7778.
Schuman, G. E., Taylor, E. M., Jr., Rauzi, F. and Pinchak,
B. A. 1985. Revegetation of mine land: influence of topsoil
depth and mulching method. J. Soil Water Conserv. 40:
249252.
Shalhevet, J. and Bernstein, L. 1968. Effects of vertically
heterogeneous soil salinity on plant growth and water uptake.
Soil Sci. 106: 8593.
Shalhevet, J., Reiniger, P. and Shimshi, D. 1969. Peanut
response to uniform and non-uniform soil salinity. Agron. J.
61: 384387.
Staples, T. E. and Van Rees, K. C. J. 2001. Wood/sludge ash
effects on white spruce seedling growth. Can. J. Soil Sci. 81:
8592.
Stolte, W. J., Barbour S. L. and Boese C. D. 2000. Reclamation
of saline-sodic waste dumps associated with the oil sands
industry. In Proc. Can. Land Reclamation Conf. [CD-ROM],
Edmonton, AB. 2000 Sep, 1720. CLRA, Edmonton, AB.
KESSLER ET AL. * SALINIZATION OF SOILS OVER OIL SAND SPOIL
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
Stott, D. F. and Aitken, J. D. 1993. Interior platform, western
basins and eastern cordillera; geological exploration of
the interior plains. Pages 1530 in Sedimentary cover of
the Craton in Canada. Geological Survey of Canada, Ottawa,
ON.
Sumner, M. E., Rengasamy, P. and Naidu, R. 1998. Sodic soils:
a reappraisal. Pages 317 in M. E. Sumner and R. Naidu, eds.
Sodic soils distribution, properties, management, and
environmental consequences. Oxford University Press,
New York, NY.
Sydnor, R. S. and Redente, E. F. 2000. Long-term
plant community development on topsoil treatments overlying
647
a phytotoxic growth medium. J. Environ. Qual. 29:
17781786.
Tanji, K. K. (ed.). 1990. Agricultural salinity assessment and
management. ASCE Manuals and Reports on Engineering
Practice No. 71. American Society of Civil Engineers,
New York, NY.
Wall, S. N. 2005. Characterizing geochemical reactions
in an overburden waste pile: South Bison Hill, Syncrude,
Canada. M.Sc. thesis, University of Saskatchewan, Saskatoon,
SK.
Zill, D. G. and Cullen, M. R. 1992. Advanced Engineering
Mathematics. PWS Publishing Company, Boston, MA.
This article has been cited by:
Can. J. Soil. Sci. Downloaded from pubs.aic.ca by Ms Amy Heidman on 01/09/13
For personal use only.
1. Lilles E.B. , Purdy B.G. , Macdonald S.E. , Chang S.X. . 2012. Growth of aspen and white spruce on naturally saline sites
in northern Alberta: Implications for development of boreal forest vegetation on reclaimed saline soils. Canadian Journal of
Soil Science 92:1, 213-227. [Abstract] [Full Text] [PDF] [PDF Plus]
2. Heidi Lazorko, Ken C. J. Rees. 2011. Root Distributions of Planted Boreal Mixedwood Species on Reclaimed Saline–Sodic
Overburden. Water, Air, & Soil Pollution . [CrossRef]