Textural interfaces affected the distribution of roots, water, and nutrients in some reconstructed forest soils in the Athabasca oil sands region

Ecological Engineering 64 (2014) 240–249

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Textural interfaces affected the distribution of roots, water, and nutrients in some reconstructed forest soils in the Athabasca oil sands region Kangho Jung a,b , Min Duan a , Jason House a , Scott X. Chang a,∗ a b

Department of Renewable Resources, 442 Earth Sciences Building, University of Alberta, Edmonton, Alberta, Canada T6G 2E3 Soil and Fertilizer Division, National Academy of Agricultural Science, 150 Suinro, Kweonseonku, Suwon 441-707, Republic of Korea

a r t i c l e

i n f o

Article history: Received 5 August 2013 Received in revised form 8 November 2013 Accepted 20 December 2013 Available online 28 January 2014 Keywords: Fine root Land reclamation Overburden Tailings sand Textural discontinuity

a b s t r a c t Re-constructed soils in the reclaimed landscape in the Athabasca oil sands region (AOSR) usually consist of an upper amendment layer (cover soil) and a substrate layer below. The cover soil used is typically peat-mineral mix (PMM) and the substrate can be materials such as tailings sand (TS) and fine-textured overburden (OB) materials. Abrupt changes in soil properties between the cover soil and the lower substrate layer create the so-called textural interface that can restrict water and nutrient movement and subsequently affect root growth. To assess the effect of the textural interface on the distribution of roots, water, and nutrients, we collected soil samples from the 10–5, 5–2, and 2–0 cm layers above and 0–2, 2–5, and 5–10 cm layers below the interface (zero at the interface) from nine sites each of PMM/TS and PMM/OB that were planted to lodgepole pine (Pinus contorta) and white spruce (Picea glauca) trees, respectively. Fine root (<2 mm) biomass (FRB) decreased logarithmically (p < 0.01) through the interface. The greatest decrease was found between 5–2 and 2–0 cm above the interface in TS due to lack of capillary rise of water and at the interface in OB due to compaction of fine-textured OB material. Based on stepwise regression analysis, volumetric water content and NH4 -N or DON explained the variation of FRB in TS while electrical conductivity (EC) was the main parameter explaining FRB in OB. Our results indicate that management practices need to consider the influence of textural discontinuity or textural interface on the distribution of fine roots, water and nutrients and for water and N availability in TS and salt stress in OB as potential limiting factors for improving tree growth in the reclaimed/reconstructed landscape in the AOSR. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Abrupt changes in soil texture in a soil profile create boundaries or textural interfaces between soil layers. The so-called textural interface or discontinuity can restrict water and nutrient movement (Li and Liu, 2011) and can subsequently affect root growth (Eapen et al., 2005). Soil profiles with a textural interface could be classified into two types: a fine-textured layer over a coarsetextured one and the reversed textural arrangement of soil layers. Permeability typically reduces at the interface in both types of layer configurations through a reduction in the rate of water movement through the interface (Jury and Horton, 2004; Li et al., 2013). When a fine-textured soil layer with principally micropores overlies a sandy layer, percolation water is stagnant just above the textural interface, as water cohesion and capillary pressure in

∗ Corresponding author. Tel.: +1 780 492 6375; fax: +1 780 492 1767. E-mail addresses: [email protected] (K. Jung), [email protected] (M. Duan), [email protected] (J. House), [email protected] (S.X. Chang). 0925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ecoleng.2013.12.037

micropores prevent water from infiltrating into macropores of the coarse-textured lower layer (Boateng, 2007). This capillary barrier phenomenon has been used to prevent water that infiltrated into the cover layer from getting into a lower layer in landfills (Qian et al., 2010) and to increase water availability in the rooting zone above the capillary barrier (Ityel et al., 2011). Similarly, water easily accumulates above the interface between an upper coarse-textured soil and a lower clayey and/or compacted soil, because water infiltrates very slowly into the lower layer (Verbist et al., 2007). Water availability in the layer above the interface again increases in this scenario (Li and Liu, 2011), but poor drainage may induce locally reduced (or anaerobic) conditions and decrease nutrient availability (Brady and Weil, 2008). Therefore, water movement across the textural interface can become limited and the distribution of water and nutrients can be distorted in such soil profiles. The Athabasca oil sands region (AOSR) in Alberta, Canada, is the world’s second largest reserve of recoverable oil (Humphries, 2008). Unlike conventional crude oil extraction, open-pit mining of oil sands has disturbed and will continue to disturb a large amount of surface land area. Such disturbances include the removal

K. Jung et al. / Ecological Engineering 64 (2014) 240–249

of vegetation and soil. Alberta’s Environmental Protection and Enhancement Act requires that all mines must be reclaimed to the equivalent land capability of the area prior to surface mining (Powter et al., 2012). To fulfil that requirement, it is important to reconstruct soils that are capable of supporting sustained tree growth, with potential growth limiting factors minimized. As fine roots perform water and nutrient uptake, fine root biomass (FRB) has been used to indicate environmental changes and stand characteristics (Jung and Chang, 2013; Vanguelova et al., 2007). FRB has also been reported to be significantly correlated with tree growth (Finér et al., 2007). Therefore, FRB may be used as an indicator of ecosystem development in the reclaimed landscape. The first step in land reclamation in the oil sands mining areas is soil re-construction (Naeth et al., 2011). Reconstructed soils in the AOSR usually consist of an upper layer of amendments of peat or peat-mineral mix (PMM) and lower layers of substrates such as tailings sand (TS) and/or fine-textured overburden (OB) materials (Rowland et al., 2009). The PMM is a mixture of salvaged peat and surface mineral soils and has an appropriate combination of micro- and macropores that help with both drainage and water storage (Hejduk et al., 2012) while TS and OB mainly contain macro- and micropores, respectively. Therefore, differences in the pore structure between the amendment and substrate layers may distort the distribution of water and nutrients and subsequently influence root growth across the interface. For example, soil profiles with the amendment over TS may have advantages in drainage, but water and nutrient movement by capillary rise across the interface is likely limited due to lack of micropores in the TS layer. Given the low water and nutrient holding capacity of TS (Barbour et al., 2007), potential water and nutrient deficiency may suppress root growth below the interface. Furthermore, water availability decreases in the amendment layer and may become a limiting factor for tree growth as capillary rise does not occur in a TS type soil profile. In soil profiles with the PMM over fine-textured OB, the hydraulic conductivity of the fine-textured OB is expected to be much lower than that of the PMM (Barbour et al., 2007), meaning that water infiltrated into the PMM would be mainly stored in the amendment layer as drainage through the interface would be restricted. In addition, when the OB layer is compacted, it would have high soil strength and root extension beyond the interface would be limited (Khan et al., 2012). Therefore, the textural interface between the amendment and OB layers can be a barrier for root growth as well. In this study, we tested the hypothesis that the distribution of FRB and nutrients in reconstructed soil profiles is affected by the textural interface in reclaimed soils in the AOSR. We also investigated the impact of the textural interface on soil properties and factors affecting FRB distribution in reclaimed soils. We expect that this study will provide information that can help improve land reclamation practices in the AOSR.

2. Materials and methods 2.1. Site description This research was carried out on one of the Suncor Energy Inc. leases located at about 22 km north of Fort McMurray in the AOSR. A portion of this land was reclaimed from open-pit mining sites to upland forests. The research area was located in the humid continental climate zone having short warm summers and long cold winters; the mean annual temperature is 0.7 ◦ C with 67% mean annual humidity and the mean annual precipitation is 455.7 mm with an average of 342.2 mm occur as rainfall during the growing season (Environment Canada, 2010). The reclaimed soils have been

241

re-established with PMM as amendments above reclamation substrates such as TS and OB materials. Lodgepole pine (Pinus contorta) and white spruce (Picea glauca) were the only tree species planted in TS and OB sites, respectively, in the studied reclaimed areas. Tree age was different from site to site (Table 1). The understory plant communities on TS sites were dominated by Rosa acicularis (prickly rose), Rubus idaeus (raspberry), Melilotus spp. (sweet clover), Taraxacum officinale (dandelion), and Agropyron trachycaulum (slender wheat grass), while Salix spp. (willow), Alnus crispa (green alder), sweet clover, dandelion, and Calamagrostis canadensis (bluejoint grass) were the dominant species on OB sites. We set up eighteen research plots 10 m × 10 m in size in the reclaimed areas, with nine plots constructed with PMM over TS and the other nine plots constructed with PMM over fine-textured OB (Table 1). The thickness of the amendment ranged from 11 to 48 cm (Table 1). The nine sites in each site type encompassed a site productivity gradient from low to high based on visual inspection of tree performance and later confirmed by tree growth increment measurements (Duan et al., unpublished data). 2.2. Sampling and analyses Each plot was surveyed in 2011 and soil samples were collected by horizon from a soil pit dug in each plot. To measure bulk density (BD), soil samples were collected with a 100 cm3 steel ring sampler and oven-dry mass of the soil in each sampler was determined. Total carbon (C) and nitrogen (N) contents were determined with a Carlo Erba NA 1500 elemental analyzer (Carlo Erba Instruments, Italy). Soil texture was analyzed using the hygrometer method (Gee and Or, 2002). Within each plot, soil samples were collected in September 2012 from the top 10 cm of the amendment with a bi-partite root auger (Eijkelkamp, the Netherlands) at 25 cm from the trunk of three randomly selected trees. Fresh samples were weighed and crushed to pass through an 8-mm sieve. Fine roots (<2 mm diameter) of the tree species were picked up on the sieve, rinsed with running water, dried at 70 ◦ C in an oven, and weighed. Three sub-samples were collected from the soil that had passed through the sieve and weighed. FRB in the sub-samples was determined. The total FRB is the sum of the two fine root samples described above. Diameter at breast height (130 cm above ground) (DBH) and height of each tree in the plots were measured in September 2011 and 2012. Aboveground tree biomass (AB) in each plot in 2011 and 2012 was calculated with DBH and height-based allometric equations (Lambert et al., 2005) and the difference between aboveground tree biomass in 2011 and 2012 was regarded as the annual increment of aboveground tree biomass (IAB). The gravimetric soil water content for the soil samples was determined in a forced-air oven at 105 ◦ C and volumetric soil water content (VWC) was calculated from bulk density and gravimetric water content. Another soil sampling was carried out in August 2012 to determine the distribution of FRB, water content, and nutrient concentrations through the textural interface. We collected soils from 10–5, 5–2, and 2–0 cm above (in the amendment layer) and 0–2, 2–5, and 5–10 cm below (in the substrate layer) the textural interface at the same location from which we collected the top 10 cm of the amendment in each plot (described above). In this sampling, the zero point was set at the textural interface. Root biomass and soil water content were determined as described above. Soil pH, electrical conductivity (EC), and concentrations of soluble cations including Ca2+ , Mg2+ , K+ , Na+ , and Al3+ were determined after extraction with deionized water at 1:2 of soil to water ratio (v:v, same below) and filtration; a 1:4 ratio was used for the PMM sample from site 15 due to the high organic matter content at this site (Table 1). A Perkin Elmer Elan 6000 quadrupole

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K. Jung et al. / Ecological Engineering 64 (2014) 240–249

Table 1 Characteristics of the studied reclaimed forest sites in the Athabasca oil sands region. Site typea

Site no.

Yearb

Location Latitude

Longitude

Amendment

Substrate c

Thickness (cm)

Bulk density (Mg m−3 )

Total C (g kg−1 )

Texture

Bulk density (Mg m−3 )

TS

1 2 3 4 5 6 7 8 9

N 56◦ 59 02  N 56◦ 58 38  N 56◦ 59 30  N 56◦ 58 55  N 56◦ 58 42  N 56◦ 59 47  N 56◦ 58 54  N 56◦ 58 45  N 56◦ 59 25 

W 111◦ 27 04  W 111◦ 27 39  W 111◦ 27 15  W 111◦ 29 58  W 111◦ 27 51  W 111◦ 28 14  W 111◦ 31 04  W 111◦ 27 24  W 111◦ 27 04.4 

1996 1991 1996 1992 1991 1991 1992 1991 1996

17 14 14 30 18 24 12 22 30

0.8 1.1 1.0 0.8 0.9 0.6 1.2 1.4 1.0

67 65 50 79 62 160 15 85 51

SCL SCL SL SCL SCL SCL SCL SCL SCL

1.5 1.1 1.4 1.5 1.4 1.6 1.2 1.6 1.3

OB

10 11 12 13 14 15 16 17 18

N 56◦ 59 09  N 56◦ 59 24  N 56◦ 59 51  N 56◦ 59 50  N 56◦ 59 34  N 57◦ 01 25  N 56◦ 59 31  N 56◦ 59 48  N 56◦ 59 30 

W 111◦ 32 07.6  W 111◦ 32 08.7  W 111◦ 32 40.2  W 111◦ 32 18  W 111◦ 32 00  W 111◦ 30 02  W 111◦ 32 13  W 111◦ 32 36  W 111◦ 31 56 

1982 1991 1991 1992 1992 1984 1991 1992 1992

20 11 27 16 14 25 48 26 20

0.9 1.2 1.2 0.8 0.9 0.3 0.9 1.0 1.2

49 45 48 73 59 235 56 170 53

SCL SCL SCL SCL SCL N/A SCL SCL SCL

1.6 1.5 1.4 1.1 1.4 1.4 1.3 1.5 1.6

Total C (g kg−1 ) 0.9 1.7 2.5 2.2 2.6 2.9 2.0 1.6 0.6 29 42 45 39 45 34 36 43 41

Texture

S S S S S S S S S SCL SCL SCL SCL SCL CL SCL SCL SCL

a TS is a soil profile type with tailings sand substrate below the amendment and OB is a soil profile type with fine-textured overburden material below the amendment. Lodgepole pine and white spruce were planted on tailings sand (TS) and overburden (OB), respectively. b Year is when trees were planted after soil reconstruction. c S, SL, SCL and CL stand for sand, sandy loam, sandy clay loam and clay, respectively.

ICP-MS (Perkin Elmer, Inc., Shelton, CT) was used to determine soluble cation concentrations. A 1 mol L−1 KCl was used to extract dissolved organic C (DOC) and N (DON) and NH4 -N and NO3 -N at a 1:5 ratio of soil to solution. Dissolved C and N were analyzed with a TOC-Vcsn with TNM-1 (Shimadzu, Japan). Dissolved C concentration was used for DOC concentration as no inorganic C was found in the soil. Available NH4 -N and NO3 -N concentrations were determined using the indophenol blue method and the colorimetric method with vanadium, sulfanilamide and N-(1-naphthyl) ethylenediamine, respectively. The DON concentration was calculated by subtracting the sum of NH4 -N and NO3 -N concentrations from the total dissolved N concentration.

2.3. Statistical analyses Correlation analysis was performed among AB, IAB, FRB in the surface 10 cm of the amendment or in the entire depth of the amendment, stand age, and the thickness of the amendment. To determine the relationship between IAB and other variables (AB, stand age, the amendment thickness and FRB), a stepwise regression analysis was conducted with bidirectional elimination; the significance level of both entry into and staying in the model was set at 0.05. Paired-t test was conducted to examine the discontinuity of soil properties between soil layers above and below the interface. Correlation analysis was also performed to determine relationships among soil properties between 10 cm above and 10 cm below the interface. As data points in each scatter plot clustered in the lower left corner except for pH, BD, and the median depth of layers, logarithmic transformations were performed before the correlation analysis for most variables except for pH, BD, and the median depth of layers. Based on the scatter plots, the stepwise regression equations for the FRB at 10 cm above and 10 cm below the interface, respectively, were set up as follows: Log(FRB) = ˛(pH) + ˇ(BD) + (Median depth) + a Log(x1 ) + b Log(x2 ) + · · · + n Log(xn ) + c

where xi is one of the soil properties except for pH, BD, and the median depth, and ˛, ˇ, , a, b, n, and c are coefficients. An ˛ value of 0.05 was chosen to indicate statistical significance of correlation and regression analyses. All statistical analyses were performed using version 9.01 of SAS (SAS Institute Inc., Cary, NC). 3. Results 3.1. Fine root biomass and its relationship with tree growth The FRB in the surface 10 cm cover soil and in the whole cover soil layer were positively correlated with IAB (p < 0.01 for all cases) but stand age and the thickness of the amendment did not show any significant relationship with IAB (Table 2). The AB and IAB was positively correlated in TS (p < 0.05) but not in OB (Table 2). Based on the regression analysis, the FRB was the only variable that contributed to explain IAB. The FRB in the top 10 cm PMM and in the whole PMM layer explained 69% (p < 0.001) and 47% (p < 0.01), respectively, of IAB in TS and 81% (p < 0.001) and 57% (p < 0.01), respectively, of IAB in OB (Fig. 1). This indicates that the FRB and aboveground tree growth were strongly related in the studied reclaimed sites in AOSR. 3.2. Distribution of fine root biomass The FRB decreased with increasing depth (p < 0.01) between 10 cm above and 10 cm below the textural interface in both TS and OB (Tables 3 and 4) while the distribution patterns were different between substrates (Fig. 1). In TS, the FRB dramatically reduced (p < 0.01) between 10–5 cm and 5–2 cm above the interface. Except for this case, the difference in FRB between adjacent layers was not significant. On the other hand, changes in FRB between adjacent layers were found only between 2–0 cm above and 0–2 cm below the interface (p < 0.05), implying that changes in FRB was directly affected by the textural interface. The FRB in the 5–10 cm layer below the interface was minimal in both TS and OB and ranged from 0.1 to 2.8 kg m−3 in TS and from 0.01 to 2.3 kg m−3 in OB. The coefficient of variation of FRB in the layers 10 cm above and 10 cm

K. Jung et al. / Ecological Engineering 64 (2014) 240–249

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Table 2 Pearson correlation coefficients (r) and probability (p) between the annual increment of aboveground biomass and other factors in both tailings sand (TS) and overburden (OB) substrates. TS

r p a b c

OB

ABa

Stand age

Amendment thickness

FRB 10b

FRB Ac

AB

Stand age

Amendment thickness

FRB 10

FRB A

0.63 0.07

0.27 0.48

0.08 0.85

0.83 0.006

0.68 0.04

0.18 0.64

0.39 0.30

0.04 0.91

0.90 0.001

0.75 0.02

Aboveground biomass. Fine root biomass in surface 10 cm. Fine root biomass in the entire amendment layer.

below the interface ranged from 11 to 31% in TS and from 28 to 49% in OB, implying more heterogeneous conditions for fine root growth between OB sites compared to those between TS sites. 3.3. Distribution of water and nutrients The VWC decreased with depth (p < 0.001) below the interface in TS, but did not significantly change between layers above the interface in TS and both above and below the interface in OB (Fig. 2). The variation of VWC among sites decreased with depth in TS, with the standard error of the mean only 0.4% at the 5–10 cm layer below the interface. The pH showed a similar distribution/variation with depth to that of VWC. The EC had a decreasing trend below the

interface in TS but had an increasing trend in OB. In TS the DOC concentration decreased with depth (p < 0.001) in layers below the interface, while no change in DOC concentration was found in layers above the interface, indicating influences of the interface on DOC concentration. The DOC in OB and DON in both TS and OB were not different between layers across the interface in OB. Concentrations of NH4 -N and NO3 -N did not show any significant trend with depth across the interface in both TS and OB. The dominant form of available N was NH4 -N, which accounted for 76% of the total inorganic N concentration. In TS, soluble Ca2+ and Mg2+ decreased with depth (p < 0.05) between 2–0 cm above and 0–2 cm below the interface consistent with the decrease of EC with depth, indicating effects of textural interface on those soluble salts. Soluble cations in OB, however, did not show any significant change across the interface. 3.4. Relationships among fine root biomass and soil properties In TS, Log(FRB) was positively correlated with Log(VWC) (p < 0.001), Log(DOC), Log(NH4 -N), Log(Mg2+ ) (p < 0.01), pH, and Log(Na+ ) (p < 0.05) and negatively correlated with Log(amendment thickness) (p < 0.05) when considered for both layers above and below the interface (Table 3). Based on the stepwise multiple regression analysis, Log(FRB) in the 0–10 cm layer above the interface was explained by pH, Log(VWC), and Log(NH4 -N) (R2 = 0.49, p < 0.01) and Log(FRB) in the 0–10 cm layer below the interface (tailings sand) was explained by Log(VWC) and Log(DON) (R2 = 0.38, p < 0.01) (Table 5). Other variables such as Log(DOC) did not explain Log(FRB). In OB, Log(FRB) was positively correlated with Log(DON) (p < 0.01) and negatively correlated with EC, Log(VWC), Log(Ca2+ ), Log(Mg2+ ) (p < 0.001), and pH (p < 0.01) when considered for both layers above and below the interface (Table 4). The Log(EC), however, was the only variable that explained Log(FRB) in the 0–10 cm layer above the interface (PMM) and pH, the median depth, and Log(K+ ) as well as Log(EC) explained Log(FRB) in the 0–10 cm layer below the textural interface (Table 5). 4. Discussion 4.1. Factors affecting FRB in the amendment/TS profiles

Fig. 1. Relationships between annual increment of aboveground tree biomass (IAB) and fine root biomass (FRB) in the top 10 cm of the amendment (FRB 10) or the whole amendment layer (FRB A) in reclaimed soils in the Athabasca oil sands region, Alberta, Canada. The TS site consists of a tailings sand layer below the amendment and OB has a fine-textured overburden layer below the amendment. The asterisks indicate the significance of the regression lines, with ** and *** indicating p < 0.01 and p < 0.001, respectively.

The FRB in TS decreased with depth between 10 cm above and 10 cm below the interface, accompanying the decrease of VWC, pH, DOC, and soluble cations. As root litter is one of the major sources of dissolved organic matter in the soil solution (Uselman et al., 2009), FRB distribution was likely one of the factors affecting DOC concentrations in the soil. On the other hand, water and cationic nutrient availabilities were likely potential limiting factors for fine root growth. Low soil water availability has been observed to reduce fine root growth in forest ecosystems (Gleeson and Good, 2010; Yavitt and Wright, 2001); plants under limited water availability

244 Table 3 Pearson correlation coefficients between soil properties based on data of the 10–5, 5–2, and 2–0 cm layers above and 0–2, 2–5, and 5–10 cm layers below the textural interface between amendments and tailings sand in reclaimed soils in the Athabasca oil sands region, Alberta, Canada. Numbers in parentheses refer to p values and bold numbers indicate significant correlation coefficients.

Median deptha Log(FRB)b BDc Log(VWC)d

Log(EC) Log(DOC) Log(DON) Log(NH4 -N) Log(NO3 -N) Log(Ca2+ ) Log(Mg2+ ) Log(K+ ) Log(Na+ )

BDc

Log(VWC)d

pH

Log(DOC)

Log(DON)

Log(NH4 -N)

Log(NO3 -N)

Log(Ca2+ )

Log(Mg2+ )

Log(K+ )

Log(Na+ )

Log(Al3+ )

0.52 (<0.01)

−0.60 (<0.01)

0.65 (<0.01)

0.64 0.49 (<0.01) (<0.01)

0.53 (<0.01)

0.21 (0.13)

0.16 (0.25)

0.08 (0.57)

0.52 (<0.01)

0.51 (<0.01)

−0.08 (0.55)

0.33 (0.01)

−0.46 (<0.01)

−0.20 (0.16)

0.50 (<0.01)

0.32 (0.02)

0.43 (<0.01)

0.24 (0.08)

0.35 (0.01)

0.07 (0.63)

0.27 (0.05)

0.35 (0.01)

0.21 (0.14)

0.33 (0.02)

−0.09 (0.50)

−0.40 (<0.01)

−0.59 −0.38 (<0.01) (<0.01)

−0.23 (0.10)

−0.16 (0.26)

0.05 (0.74)

0.16 (0.25)

−0.29 (0.03)

−0.26 (0.06)

0.27 (0.05)

−0.05 (0.71)

0.36 (0.01)

0.75 0.70 (<0.01) (<0.01)

0.84 (<0.01)

0.69 (<0.01)

0.53 (<0.01)

−0.25 (0.07)

0.78 (<0.01)

0.78 (<0.01)

0.11 (0.41)

0.67 (<0.01)

−0.56 (<0.01)

0.59 (<0.01)

0.64 (<0.01)

0.41 (<0.01)

0.16 (0.25)

−0.31 (0.03)

0.62 (<0.01)

0.52 (<0.01)

0.00 (0.99)

0.43 (<0.01)

−0.52 (<0.01)

0.61 (<0.01)

0.61 (<0.01)

0.37 (0.01)

−0.24 (0.08)

0.87 (<0.01)

0.84 (<0.01)

0.12 (0.39)

0.37 (0.01)

−0.47 (<0.01)

0.72 (<0.01)

0.61 (<0.01)

−0.06 (0.68)

0.75 (<0.01)

0.77 (<0.01)

0.25 (0.07)

0.71 (<0.01)

−0.40 (<0.01)

0.79 (<0.01)

−0.33 (0.02)

0.68 (<0.01)

0.66 (<0.01)

0.25 (0.07)

0.56 (<0.01)

−0.52 (<0.01)

−0.19 (0.18)

0.42 (<0.01)

0.47 (<0.01)

0.17 (0.21)

0.48 (<0.01)

−0.30 (0.03)

−0.15 (0.30)

−0.11 (0.45)

0.18 (0.20)

0.09 (0.54)

0.13 (0.34)

0.96 (<0.01)

0.20 (0.14)

0.58 (<0.01)

−0.59 (<0.01)

0.23 (0.10)

0.60 (<0.01)

−0.50 (<0.01)

0.50 (<0.01)

−0.02 (0.90)

Log(EC)

0.27 (0.05)

−0.48 (<0.01)

a Median depth refers to the median depth of each soil layer sampled with zero point at the interface. For example, 1 cm as the median depth for the 2–0 cm layer above the interface and −1 cm for the 0–2 cm layer below the interface. b Fine root biomass. c Bulk density. d Volumetric water content.

K. Jung et al. / Ecological Engineering 64 (2014) 240–249

pH

Log(FRB)b

Table 4 Pearson correlation coefficients between soil properties based on data of the 10–5, 5–2 and 2–0 cm layers above and 0–2, 2–5, and 5–10 cm layers below the textural interface between amendments and fine-textured overburden in reclaimed soils in the Athabasca oil sands region, Alberta, Canada. Numbers in parentheses refer to p values and bold numbers indicate significant correlation coefficients.

a

Median depth Log(FRB)b BDc Log(VWC)d

Log(EC) Log(DOC) Log(DON) Log(NH4 -N) Log(NO3 -N) Log(Ca2+ ) Log(Mg2+ ) Log(K+ ) Log(Na+ )

BD

Log(VWC)

pH

Log(EC)

Log(DOC)

Log(DON)

Log(NH4 -N)

Log(NO3 -N)

Log(Ca2+ )

Log(Mg2+ )

Log(K+ )

Log(Na+ )

Log(Al3+ )

0.44 (<0.01)

−0.61 (<0.01)

−0.19 (0.16)

−0.13 (0.35)

−0.03 (0.81)

0.14 (0.33)

0.18 (0.19)

−0.30 (0.03)

−0.03 (0.81)

−0.21 (0.13)

−0.25 (0.07)

−0.33 (0.02)

−0.05 (0.70)

−0.04 (0.77)

−0.15 (0.29)

−0.53 (<0.01)

−0.39 (<0.01)

−0.54 (<0.01)

−0.07 (0.63)

0.42 (<0.01)

0.22 (0.11)

−0.04 (0.77)

−0.57 (<0.01)

−0.56 (<0.01)

−0.05 (0.72)

−0.22 (0.11)

0.06 (0.65)

0.07 (0.60)

0.39 (<0.01)

−0.24 (0.07)

0.04 (0.77)

0.03 (0.81)

0.38 (0.01)

−0.10 (0.49)

0.17 (0.22)

0.04 (0.80)

0.20 (0.15)

−0.33 (0.01)

0.06 (0.69)

0.26 (0.06)

0.54 (<0.01)

0.33 (0.01)

−0.27 (0.05)

−0.17 (0.22)

0.01 (0.96)

0.49 (<0.01)

0.51 (<0.01)

0.31 (0.02)

0.42 (<0.01)

0.17 (0.23)

0.19 (0.16)

−0.24 (0.08)

−0.18 (0.19)

−0.35 (0.01)

−0.05 (0.71)

0.35 (0.01)

0.22 (0.11)

0.05 (0.74)

−0.03 (0.82)

0.10 (0.49)

0.09 (0.52)

−0.66 (<0.01)

−0.38 (<0.01)

−0.04 (0.80)

0.82 (<0.01)

0.90 (<0.01)

0.44 (<0.01)

0.53 (<0.01)

−0.19 (0.17)

0.16 (0.24)

0.25 (0.07)

−0.09 (0.51)

0.16 (0.24)

0.17 (0.23)

−0.09 (0.53)

−0.09 (0.50)

−0.10 (0.46)

0.38 (<0.01)

0.05 (0.73)

−0.63 (<0.01)

−0.59 (<0.01)

−0.47 (<0.01)

−0.24 (0.08)

0.24 (0.08)

0.11 (0.45)

−0.14 (0.32)

−0.10 (0.45)

0.02 (0.87)

−0.32 0.02

−0.19 (0.17)

−0.03 (0.85)

−0.04 (0.79)

−0.09 (0.53)

−0.01 (0.96)

0.01 (0.95)

0.92 (<0.01)

0.38 (<0.01)

0.05 (0.73)

−0.38 (<0.01)

0.46 (<0.01)

0.32 (<0.01)

−0.34 (<0.01)

0.39 (<0.01)

0.09 (0.53)

K. Jung et al. / Ecological Engineering 64 (2014) 240–249

pH

Log(FRB)

0.27 (0.05)

a Median depth refers to the median depth of each soil layer sampled with zero point at the interface. For example, 1 cm as the median depth for the 2–0 cm layer above the interface and −1 cm for the 0–2 cm layer below the interface. b Fine root biomass. c Bulk density. d Volumetric water content.

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K. Jung et al. / Ecological Engineering 64 (2014) 240–249

may shift allocation of C towards roots, increasing root to shoot ratio (Kozlowski and Pallardy, 2002) and specific root length and specific root surface area to cope with water limitation (Metcalfe et al., 2008). In this study, low water holding capacity and water availability in the TS layer (Fig. 2) likely reduced root growth below the interface (Barbour et al., 2007). In single-layered soils, water potential typically increases with depth because of loss of water to the atmosphere at the soil surface (Kirkham, 2005). In the studied soil, lack of micropores in the TS

layer would decrease soil water potential abruptly when a small amount of water is consumed in the TS layer and that prevents capillary rise of water to the PMM layer (Boateng, 2007), which can reduce the water potential of the lower part of the PMM layer as compared to the upper part of the PMM (Fig. 2). Given that the studied reconstructed soil profiles had various thickness of the PMM layer (Table 1), reduction of FRB with depth at 2–5 cm above the interface was likely a response to the decreased VWC below the interface. Therefore, it is important to have a PMM layer

Fig. 2. Distribution of fine root biomass (FRB), volumetric soil water content (VWC) and soil chemical properties (such as DOC-dissolved organic carbon and DON-dissolved organic nitrogen) between 10 cm above (in the amendment layer) and below (in the substrate layer) the textural interface. The TS consisted of a tailings sand layer below the amendment and OB had a fine-textured overburden layer below the amendment. The zero point in depth is the textural interface. The error bars are standard errors of means.

K. Jung et al. / Ecological Engineering 64 (2014) 240–249

247

Fig. 2. (Continued ).

deep enough to store available water because water supply to roots would be limited in the lower part of PMM layers. Additionally, the potential impact of water deficiency can be mitigated when TS sites are established in lower slope or level positions of the landscape with relatively shallow groundwater table (Jury and Horton, 2004). Low nutrient availability can be another factor that limits root growth (McGrath et al., 2001; Raich et al., 1994). However, it is difficult to conclude that decreasing cationic nutrient concentrations caused FRB to decrease with depth in this study. Soluble Ca2+ , Mg2+ , and Na+ concentrations were significantly related to VWC

and based on the stepwise regression analysis these ions did not help explain any additional variance on top of what was explained by VWC (Table 5). This suggests that effects of cationic nutrients on FRB are possibly dependent on water availability in TS (Gleeson and Good, 2010). On the other hand, N availability represented as NH4 -N in the PMM and DON in the TS layers explained variations in FRB (Table 5). Given that the vertical distributions of NH4 -N and DON were different from that of FRB and VWC (Fig. 2), spatial variation of NH4 -N and DON likely affected the variation in the distribution of FRB in TS sites. Nitrogen has been often reported as

Table 5 Regression equations for the relationship between fine root biomass within 10 cm above and below the textural interface between the amendment and substrate in reclaimed forest soils and variables selected by stepwise multiple regression analyses. Site type

Layer

Regression equationa

Amendment over tailings sand

10–0 cm above the interface

Log(FRB) = 0.66 Log(VWC) + 0.38 Log(NH4 N) − 0.49 pH + 2.67 (R2 = 0.49, p < 0.001) Log(FRB) = 0.59 Log(VWC) − 0.40 Log(DON) (R2 = 0.38, p = 0.004)

0–10 cm below the interface

Amendment over fine-textured overburden a

10–0 cm above the interface 0–10 cm below the interface

Log(FRB) = −1.00 Log(EC) + 0.12 (R2 = 0.38, p < 0.001) Log(FRB) = −1.11 Log(EC) − 0.66 pH + 0.09 (Median depth) + 1.13 Log(K+ ) + 4.57 (R2 = 0.79, p < 0.001)

FRB, VWC, DON, and EC stand for fine root biomass, volumetric water content, dissolved organic nitrogen and electrical conductivity, respectively.

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K. Jung et al. / Ecological Engineering 64 (2014) 240–249

the most limiting nutrient in reclaimed sites, especially with peatbased amendments (Hemstock et al., 2010). Our data also indicate that water and N availability affected fine root growth in TS and future reclamation efforts should be directed to reduce the risk of water and N deficiency in reclamation prescriptions with TS as a substrate. 4.2. Factors affecting FRB in the amendment/OB profiles The FRB abruptly decreased at the interface between the amendment and the OB layer in OB sites, but there was a lack of clear difference of soil properties between the amendment and the OB layer except for BD, NH4 -N, and soluble cations (Fig. 2). Increased NH4 -N and soluble cation concentrations in the OB layer were not expected to reduce FRB while compacted soils (high BD) in the OB layers were. Soil compaction increases mechanical resistance to root penetration, reducing a plant’s ability to explore a larger soil volume (Whalley et al., 2005). On the other hand, compaction of the subsoil helps to increase soil water availability by store water within the topsoil by reducing drainage; such effects can contribute to root growth in the amendment layer (Li and Liu, 2011). The relationship between FRB and BD, however, was not significant in OB sites (Table 4). As BD is also affected by other soil properties such as the type of parent material and soil texture, BD might have a limited value in indicating soil compactness when comparing different types of soils (Håkansson and Lipiec, 2000). The most important factor explaining variations in FRB in OB sites was EC. The variation of EC explained the variation of FRB among OB sites (Table 5). The FRB decreases under saline conditions; however, a part of the reduction of the total FRB/area can be compensated for by increasing specific root areas (Rewald et al., 2011). Salt stress is of concern in reclaimed soils in the AOSR because some OB materials were derived from marine shale that is highly saline (Barbour et al., 2007). The soil suitability guideline for the AOSR treats salinity as an important factor and the % of soil quality rating deduction caused by soil salinity = (15 × EC) − 20, when EC is 2 dS m−1 or greater (CEMA, 2006). The EC in OB ranged from 0.4 to 6.6 dS m−1 , with a mean of 3 dS m−1 , suggesting that a number of the OB sites in this study were exposed to salinity stress. The implication from this study is that management practices that reduce salt stress should be employed to improve tree performance on OB sites in the AOSR, as it has been already suggested that saline-sodic OB materials should be capped with a minimum of 80 cm of non-saline OB material (Barbour et al., 2007). In addition, as fine-textured OB material can be compacted more easily than coarse-textured tailings sand materials (Håkansson and Lipiec, 2000), the impact of gigantic machinery should be minimized when OB materials are worked on for reclamation. The different rooting habits between lodgepole pine and white spruce can affect the distribution of FRB through the interface in the reconstructed soil profile. Although both tree species are characterized as shallow-rooted, the different FRB distribution patterns found in this study were likely affected by both tree species characteristics and differences in soil properties between TS and OB. 5. Conclusions Land reclamation practices such as the use of different substrates for reconstructing the disturbed landscape and the associated properties of those substrates affected the distribution of FRB across the amendment-substrate interface. In both the TS and OB sites, large decreases of FRB were found between 10 cm above and below the textural interface between the upper amendment layer and the lower substrate layer, while the factors affecting FRB

were different between the substrate types. Changes in water and N availabilities explained the variation in FRB in TS profiles. On the other hand, salinity stress was the main factor causing variations in FRB among OB sites and soil compaction restricted fine root growth through the textural interface. We conclude that the textural interface created by placing soil layers with contrasting soil textures restricts fine root development. The reclamation and the subsequent management of the reclaimed sites in the AOSR should consider the impact of the textural interface and the different physico-chemical properties of the different substrates on the success of land reclamation. Acknowledgements This study was supported by the Helmholtz-Alberta Initiative (HAI) and the Land Reclamation of International Graduate School (LRIGS), which was funded by a Collaborative Research and Training Experience (CREATE) grant from the Natural Science and Engineering Council of Canada (NSERC). This research was also assisted by the Environmental Reclamation Research Group (ERRG) of Canadian Oil Sands Network for Research and Development (CONRAD) and National Academy of Agricultural Science in Korea (PJ008546). Suncor Energy provided access to the research sites and provided logistic support when the field work was conducted. References Barbour, S.L., Chanasyk, D., Hendry, J., Leskiw, L., Macyk, T., Mendoza, C., Naeth, A., Nichol, C., O’Kane, M., Purdy, B., Qualizza, C., Quideau, S., Welham, C., 2007. Soil Capping Research in the Athabasca Oil Sands Region, Volume I: Technology Synthesis. Syncrude Canada Ltd., Fort McMurray. Boateng, S., 2007. Probabilistic unsaturated flow along the textural interface in three capillary barrier models. J. Environ. Eng. 133, 1024–1031. Brady, N.C., Weil, R.R., 2008. The Nature and Properties of Soils, 14th ed. Prentice Hall, Upper Saddle River. CEMA, 2006. Land Capability Classification System for Forest Ecosystems in the Oil Sands, 3rd ed. Alberta Environment, Edmonton. Eapen, D., Barroso, M.L., Ponce, G., Campos, M.E., Cassab, G.I., 2005. Hydrotropism: root growth responses to water. Trends Plant Sci. 10, 44–50. Environment Canada, 2010. National climate data and information archive. http://climate.weatheroffice.gc.ca/climate normals/results e.html?Province= ALTA&StationName=&SearchType=&LocateBy=Province&Proximity=25& ProximityFrom=City&StationNumber=&IDType=MSC&CityName=&ParkName=& LatitudeDegrees=&LatitudeMinutes=&LongitudeDegrees=&LongitudeMinutes= &NormalsClass=A&SelNormals=&StnId=2519&autofwd=020111/22 Finér, L., Helmisaari, H., Lõhmus, K., Majdi, H., Brunner, I., Børja, I., Eldhuset, T., Godbold, D., Grebenc, T., Konôpka, B., Kraigher, H., Möttönen, M., Ohashi, M., Oleksyn, J., Ostonen, I., Uri, V., Vanguelova, E., 2007. Variation in fine root biomass of three European tree species: beech (Fagus sylvatica L.), Norway spruce (Picea abies L. Karst.), and Scots pine (Pinus sylvestris L.). Plant Biosyst. 141, 394–405. Gee, G.W., Or, D., 2002. Particle size analysis. In: Dane, J.H., Topp, C. (Eds.), Methods of Soil Analysis – Physical Method. ASA, Wisconsin, pp. 255–293. Gleeson, S.K., Good, R.E., 2010. Root growth response to water and nutrients in the New Jersey pinelands. Can. J. For. Res. 40, 167–172. Håkansson, I., Lipiec, J., 2000. A review of the usefulness of relative bulk density values in studies of soil structure and compaction. Soil Till. Res. 53, 71–85. Hejduk, S., Baker, S.W., Spring, C.A., 2012. Evaluation of the effects of incorporation rate and depth of water-retentive amendment materials in sports turf constructions. Acta Agric. Scand. Sect. B: Soil Plant Sci. 62, 155–164. Hemstock, S.S., Quideau, S.A., Chanasyk, D.S., 2010. Nitrogen availability from peat amendments used in boreal oil sands reclamation. Can. J. Soil Sci. 90, 165–175. Humphries, M., 2008. North American Oil Sands: History of Development, Prospects for the Future. Congressional Research Service. Ityel, E., Lazarovitch, N., Silberbush, M., Ben-Gal, A., 2011. An artificial capillary barrier to improve root zone conditions for horticultural crops: physical effects on water content. Irrig. Sci. 29, 171–180. Jung, K., Chang, S.X., 2013. Soil and tree chemistry reflected the cumulative impact of acid deposition in Pinus banksiana and Populus tremuloides stands in the Athabasca oil sands region in Western Canada. Ecol. Indic. 25, 35–44. Jury, W.A., Horton, R., 2004. Soil Physics, 6th ed. John Wiley & Sons, New Jersey. Khan, S.R., Abbasi, M.K., Hussan, A.U., 2012. Effect of induced soil compaction on changes in soil properties and wheat productivity under sandy loam and sandy clay loam soils: a greenhouse experiment. Commun. Soil Sci. Plant Anal. 43, 2550–2563.

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