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Buried wood is an important yet understudied component of natural and anthropogenic soils. Nutrient immobilization as a response to wood addition during oil sands' reclamation may be a concern since surface wood is salvaged with the soil, thereby becoming buried wood in reclamation cover soils. This project investigated the impact of buried wood on macronutrient supply and microbial communities in different reclamation soils. A 60-day incubation was performed with different rates and types of wood (0%–50%, aspen and pine) and four different soils: fine and coarse forest floor-mineral mix (fFFMM and cFFMM), peat-mineral mix (PMM), and peat. Analysis of macronutrient supply rates using Plant Root Simulator (PRS™) probes and a community-level physiological profiling (CLPP) to assess metabolic potential was performed at the end of the incubation period; microbial activity was measured through soil respiration during the incubation. Responses varied by soil type; however, buried wood caused nitrogen immobilization in three soils due to an increase in the C:N ratio. Soils with lower C:N ratios like fFFMM and PMM were more susceptible to immobilization with a decrease in available nitrogen by up to 95% at a 10% of wood addition. Phosphorus immobilization was observed in cFFMM, and potassium supply increased at 20% of wood and above. Soil microbial activity and metabolic potential increased but no significant changes in the soil profiles were observed. The findings of this study demonstrate that buried wood increases the soil C:N ratio and can potentially cause nitrogen immobilization when added by 10% of volume or more.

Managing fluid fine tailings (FFT) present a major cause of industrial and environmental concerns in oil sands surface mining production. A potential management solution is to dewater and cap the FFT solids for use in land reclamation. A 16 wk greenhouse study was conducted to assess whether FFT centrifuge cake with caps of various reclamation soil mixes (forest floor mineral mix, peat mineral mix, and a mixture of both) and depths (0, 5, 10, and 20 cm) would support growth of trembling aspen (Populus tremuloides — native broadleaf tree) and beaked willow (Salix bebbiana — native broadleaf shrub). Beaked willow had a much greater survival rate (100%) when grown directly in FFT cake compared with trembling aspen (16.7%). Plants grown directly in FFT cake were negatively impacted by high water content, low nitrate supply rates, and high metal concentrations with beaked willow seedlings having 10 times higher foliar concentrations of Al, Cr, and Ti compared with any other treatments. Adding soil caps substantially increased aboveground biomass for both species, but differences among soil cap types and depths did not have as significant of an effect on plant growth. Results from this study show that capping FFT substantially improves woody plant growth, and S. bebbiana and P. tremuloides are potentially suitable species for tailings reclamation.

Land reclamation in the Athabasca oil sands region requires construction of entire soil profiles from materials salvaged during mining. Although much attention has been paid to the limited supply of suitable topsoil materials and their impact on ecosystem recovery, suitable clean subsoil materials are also in limited supply, and their efficient and effective use is an important consideration for land managers in the region. Using data from an oil sands reclamation site in northern Alberta, Canada, we compared soil and foliar nutrients to a wildfire-impacted reference ecosystem with a similarity index. Specifically, we evaluated the similarity of forest floor-mineral mix (FFM) and peat-mineral mix (PM) as topsoil, as well as the effect of different depths of salvaged B and C horizon subsoil with PM on top. All reclamation treatments were planted with jack pine (Pinus banksiana Lamb.) and trembling aspen (Populus tremuloides Michx.), which were used to examine foliar nutrient concentrations. Individual macronutrient concentrations were different among treatments in total soil nutrients, but differences decreased in soil bioavailable nutrients and disappeared altogether in foliar nutrients. The similarity index revealed that distinct differences existed between treatments, with FFM being the most similar to the wildfire site. It also revealed a potential deficiency in foliar and soil bioavailable Mn on PM, and that increased water content of deeper subsoils had little to no effect. With use of this nutrient profile similarity index, reclamation practitioners may be able to determine if different soil prescriptions lead to higher levels of similarity to natural ecosystems more quickly.

The majority of plant diversity in North American boreal forests is comprised of understory plant communities undergoing continuous interspecific competition. Anthropogenic activities, particularly surface mining, have introduced higher severity disturbances that not only remove vegetation, but also modify soil. During reclamation, soils used to cap overburden materials have inhibited native plant growth and increased weed invasion. This study aimed to examine the effectiveness of seeding and weeding treatments for promoting the establishment of native understory plant communities, as well as a common deciduous tree species, on three different reclamation cover soils (forest floor – mineral mix, peat–mineral mix, and transitional). The broadcasting of a native forb seed mix was not successful on any of the cover soils, whereas weeding affected each cover soil differently. With weeding, the forest floor – mineral mix and transitional cover soils experienced a decrease in the relative abundance of introduced forbs and an increase in the relative abundance of graminoids. The increase in graminoid cover on the forest floor – mineral mix was mostly attributed to the expansion of Calamagrostis canadensis (Michx.) P. Beauv. Overall, weeding effectively eliminated introduced plant species, allowing competitive native grasses to establish. However, weeding may have unintentionally hindered the development of a native understory plant community via the over-establishment of grass on reclamation sites.

Northern peatlands store a globally significant amount of soil organic carbon, much of it found in rapidly thawing permafrost. Permafrost thaw in peatlands often leads to the development and expansion of thermokarst bogs, where microbial activity will determine the stability of the carbon storage and the release of greenhouse gases. In this study, we compared potential enzyme activities between young (thawed ~30 years ago) and mature (~200 years) thermokarst bogs, for both shallow and deep peat layers. We found very low potential enzyme activities in deep peat layers, with no differences between the young and mature bogs. Peat quality at depth was found to be highly humified (FTIR analysis) in both the young and mature bogs. This suggests that deep, old peat was largely stable following permafrost thaw, without a rapid pulse of decomposition during the young bog stage. For near-surface peat, we found significantly higher potential enzyme activities in the young bog than in the mature-associated with differences in peat quality derived from different Sphagnum species. A laboratory incubation of near-surface peat showed that differences in potential enzyme activity were primarily influenced by peat type rather than oxygen availability. This suggested that the young bog can have higher rates of near-surface decomposition despite being substantially wetter than the mature bog. Overall, our study shows that peat properties are the dominant constraint on potential enzyme activity and that peatland site development (successional pathways and permafrost history) through its influence on peat type and chemistry is likely to determine peat decomposition following permafrost thaw.

Foliar nutrient concentrations are commonly recommended as indicator for soil nutrient status in managed and wildland ecosystems. Using data from an oil sands mine reclamation site in Alber...

Restoring ecosystem function after oil sands surface mining involves reestablishing the biotic and abiotic ecosystem components that affect biogeochemical cycles and fluxes. In boreal forest ecosystems, pyrogenic carbon is a native soil component that affects a variety of biogeochemical parameters and biochar is its human-made analog. To evaluate the benefits of biochar amendment to reclamation cover soils, we compared characteristics and function of peat–mineral mix (PM) and forest floor–mineral mix (FFM) with and without biochar in an 18 wk greenhouse study. We assessed nutrient bioavailability (NO3, NH4, P, K, S, Mg, and Ca), foliar nutrient concentrations (N, P, K, S, Mg, Ca, Na, and Mo), soil respiration, rhizosphere polysaccharide concentration, soil organic matter stability, and Populus tremuloides Michx. seedling growth. Seedling growth increased significantly on PM cover soil with biochar. Biochar improved K nutritional status and potentially interacted with Na bioavailability in PM, affecting growth. Soil respiration significantly decreased in PM with biochar and increased in FFM. Soil organic matter stability was positively correlated with seedling growth and increased with biochar. Our findings suggest that biochar may have a significant positive effect on upland forest reclamation in the Athabasca oil sands region, especially on sites that are reclaimed with PM.

Land reclamation following surface mining in the Athabasca oils sands region will be extensive, with various challenges specific to local reclamation cover soils. The high economic costs associated with pre-disturbance soil salvage and placement in reclamation necessitates judicious management and application of salvaged cover soils. Soil microbial community activity and bioavailable nutrient supply are largely overlooked in reclamation analyses despite their potential in providing a sensitive measurement of ecosystem function. This study evaluates these parameters by comparing two continuous cover soils, a coarse-textured forest floor mineral mix (FFM) and an organic matter-rich peat soil (PM) at Syncrude Canada's Aurora Soil Capping Study. Shallow (10 cm) and Deep (20–30 cm) placement depths of FFM and PM were compared to a control receiving no cover soil and a harvested jack pine site as a reference. Soil function was assessed by measuring bioavailable nutrient supply rates, soil respiration, phospholipid fatty acid analysis (PLFA), and community level physiological profiles (CLPP). Non-metric multidimensional scaling (NMS) was used to quantify functional similarity with reference conditions. NMS revealed the greatest similarity between FFM and the reference site for bioavailable nutrient supply, PLFA, and CLPP. Deep FFM application shared greatest PLFA similarity to the reference site, while Shallow FFM was more similar in CLPP. Shallow PM was more similar to reference conditions than Deep for all parameters measured, suggesting that shallow cover soil applications might be sufficient for the reclamation target. Soil respiration rates were greatest in FFM, followed by the reference site and PM treatments, with no difference attributable to placement depth. PM had greater nitrogen and sulfur availability, but was lower in phosphorus and potassium when compared to FFM and the reference site. Ecosystem function was more similar in cover soils that mimicked the reference site conditions as much as possible, which in this case meant shallow placement and material salvaged from upland forests.

The oil extraction industry and human activity in north eastern Alberta has been growing steadily since the 1960’s and is a source of air pollution. In the late 1990’s the Wood Buffalo Environmental Association was established to monitor air quality for both public and environmental health. A primary environmental concern was soil acidification caused by sulfur (S) and nitrogen (N) deposition. A network of forest health monitoring (FHM) sites was established in dry jack pine ecosystems to serve as an early indicator of negative impacts. A sampling campaign was executed in 2011 and this study examines soil properties and foliar nutrients in the context of measured and modeled acid deposition. Total N (TN), SO42−, pH, base cation to aluminum ratio (BC:Al), and base saturation (% BS) are reported for the organic layer (LFH) and 3 depths in the mineral soil, while foliar nutrients were analysed from current annual growth in jack pine needles. Atmospheric deposition of S, N, BC, and potential acid input (PAI) in the study area was recently provided by Edgerton et al. (2019 this issue) and soil and foliar chemistry was evaluated based on deposition estimates and measurements. Inverse distance weighting was used to examine spatial patterns and regression analysis was used to quantify relationships between variables. The results indicated that S deposition is spatially correlated with foliar SO42− concentration, and LFH SO42−, but not mineral topsoil (0–5 cm) SO42−. Nitrogen deposition was spatially correlated with foliar N concentration, but not LFH or topsoil TN indicating potential uptake by the foliage or rapid uptake by roots in the LFH layer. High BC deposition in the same areas with the highest potential acid inputs (PAI) did not correlate significantly with changes in soil pH. However, LFH pH was significantly related to dry NH3 deposition, which has not been reported previously and requires further investigation.

Alberta produces large volumes of oil sands process-affected water (OSPW) as a result of bitumen extraction and upgrading processes. Naphthenic acids (NAs) and other organic acids (OAs) comprise the main constituents of OSPW that can be acutely toxic to aquatic life. The recycling, safe return or storage of OSPW into the environment is a major challenge for the oil sands industry. Therefore, proper treatment technologies that are effective but inexpensive are needed. In this study, we tested the ability of a biochar (BC) produced from wheat straw and petroleum coke (PC) to remove two model organic acids (OAs) from aqueous solution: lauric acid (LA) and 1-methylcyclohexenecarboxylic acid (MCA). The results showed that BC was generally a more effective sorbent than PC, likely because BC has higher surface area and higher functional group densities than PC. More LA than MCA sorbed to both BC and PC due to the saturated 12-carbon chain of LA which renders it more hydrophobic than MCA. An admixture of BC and PC removed more LA from solution that was expected from its component parts, which may indicate a synergy between BC and PC in removing certain OAs from solution. This study shows that BC and PC might be useful materials for on-site treatment of organic acids. However, the use of PC may also be problematic due to release of significant heavy metals and sulfur to aqueous solution.

Fire is a key driver of nutrient biogeochemistry in boreal ecosystems. Although a significant amount of research has been conducted to understand boreal fire ecology, it is still unclear how fire affects the spatial distribution of nutrients and what mechanisms are responsible for the post-fire recovery of spatial patterns. In this study, we examined spatial variability in soil nutrient bioavailability and related aboveground (AG) and belowground (BG) properties in three boreal aspen (Populus tremuloides Michx.) stands in northern Alberta at different stages of post-fire recovery. The studied sites include a 1-year old post fire stand (PF), a 9-year old stand at canopy closure (CC), and a 72-year old mature stand (MA). Ion exchange resin was used to measure nutrient bioavailability in-situ and was related to AG (vegetation and forest floor characteristics) and BG (soil microbial and chemical) properties. Significant spatial patterns were found in all three stands. PF stand had the greatest coarse scale spatial patterns (> 23 m) and availability of major macronutrients (N, P, and K). Shorter spatial range (5 to 10 m) of nutrient availability was observed in the stand with longest time since fire. Soil microbial activity was the strongest driver of nutrient availability in the PF stand, whereas contributions from aboveground variables such as understory vegetation, tree canopy cover, coarse woody debris (CWD), distance to nearest tree, and tree size was observed only in the CC and MA stands. The findings from the current study suggest that post-fire nutrient availability follows spatially predictable patterns, and confirm the hypothesis that stand replacing fire creates uniformity in nutrient availability and that the development of post-fire heterogeneity is a product of increasing ecosystem complexity.

Pyrogenic carbon (PyC), a by-product of recurrent boreal wildfires, is an important component of the global soil C pool, although precise assessment of boreal PyC stock is scarce. The overall objective of this study was to estimate total C stock and PyC stock in forest floors of Eastern Canada boreal forests. We also investigated the environmental conditions controlling the stocks and characterized the composition of the forest floor layers. Forest floor samples were collected from mesic black spruce sites recently affected by fire (3–5 yr) and analyzed using elemental analysis and solid state 13C nuclear magnetic resonance (NMR) spectroscopy. PyC content was further estimated using a molecular mixing model. Total C stock in forest floors averaged 5.7 ± 2.9 kg C/m2 and PyC stock 0.6 ± 0.3 kg C/m2. Total stock varied with position in the landscape, with a greater accumulation of organic material on northern aspects and lower slope positions. In addition, total stock was significantly higher in spruce-dominated forest floors than stands where jack pine was present. The PyC stock was significantly related to the atomic H/C ratio (R2 0.84) of the different organic layers. 13C NMR spectroscopy revealed a large increase in aromatic carbon in the deepest forest floor layer (humified H horizon) at the organic-mineral soil interface. The majority of the PyC stock was located in this horizon and had been formed during past high severity fires rather than during the most recent fire event.

Surface mining of oil sands in northeastern Alberta is a large-scale disturbance affecting over 900 km2 so far. Extraction companies are required by law to return the environment to “equivalent land capability”, but this has been challenging to quantify. To date, only one site has been certified as reclaimed. Restoring ecosystem function, including nutrient availability and uptake, might be a more realistic goal of reclamation. We tested the effect of admixing subsoil with peat and peat biochar on bioavailable nutrients, foliar nutrient concentration, and aspen (Populus tremuloides Michx.) productivity in a greenhouse study. Brunisols and luvisols, found in upland boreal forests of the Athabasca oil sands region, have high mineral soil content compared with the commonly used peat. Charcoal is a native component of boreal forest soils in northern Alberta and affects a variety of soil characteristics. In two separate tests, we compared different peat–subsoil admixtures and biochar-amended peat–subsoil admix...

Wildfire, a recurrent disturbance in the boreal, converts part of the forest floor into pyrogenic carbon (PyC). The latter is an important component of the global soil carbon pool, yet knowledge of its stocks and storage mechanisms in these boreal ecosystems is scarce. Podzolization processes, which are frequent under boreal vegetation, result in distinctive patterns of soil organic carbon (SOC) accumulation in the mineral subsoil; how this may affect PyC storage remains largely unknown. The objectives of this study were to estimate SOC and PyC stocks in podzolic soils from fire-affected black spruce forests, and to explore the storage mechanisms taking place in their mineral horizons. We also compared PyC stocks in mineral soils to forest floor stocks. Samples were collected from 23 soil profiles under black spruce forests located throughout the province of Quebec. To further explore the relationship between podzolization and PyC storage mechanisms, we measured SOC and PyC contents in size and density fractions of a subset of 11 podzolic B horizons. Total SOC stocks in the mineral horizons and forest floors were comparable. Pyrogenic carbon stocks in the mineral soils, estimated by a H 2 O 2 /dilute HNO 3 digestion, averaged 0.2 (± 0.1) kg C m − 2 . This was significantly lower than forest floor stocks, which ranged from 0.2 to 1.2 kg C m − 2 . Consequently, PyC constituted a smaller fraction of total SOC (2–15%) in mineral soils than in forest floors, where it was as high as 68% (± 5) in some horizons. In the mineral soils, SOC and PyC concentrations were strongly correlated. While some PyC was found in unprotected particulate organic matter (POM), the rest was associated with organo-mineral and organo-metallic complexes in the micro-aggregate protected POM and fine fraction. Patterns of PyC accumulation in mineral soils were similar to SOC, and the greater PyC stocks were found in podzolic B horizons.

Black carbon (BC) is an important residue of wildfires in boreal forests, but its characteristics depend on its formation conditions. The objective of this study was to characterize the chemical and physical properties of BC produced under controlled laboratory conditions, while mimicking a gradient of wildfire severity. We used fuels originating from mosses, ericaceous shrubs and spruce trees, as they constitute the major types available in boreal forests. We varied the maximum temperature (MT) from 75 to 800 °C, the duration of charring from 0.5 to 24 h and the abundance of O 2 . BC properties were analyzed using elemental analysis and proximate analysis, solid state 13 C nuclear magnetic resonance (NMR) spectroscopy, scanning electron microscopy (SEM) and surface area (SA) analysis. MT was the most significant factor affecting both chemical and physical changes. Results from 13 C NMR spectroscopy indicated that 350 °C was a threshold temperature, above which spectra became dominated by aromatic structures for all fuels. Charring duration affected BC composition at both low (250 °C for 12 h vs. 24 h) and high (600 °C for 0.5 h vs. 6 h) MT. The presence of O 2 influenced BC composition mainly at low MT (250 °C) and resulted in accelerated alkyl C degradation, accompanied with a distinct decrease in yield. Results from the SA analysis and the SEM micrographs showed that fuel type influenced BC physical properties, with moss-derived BC presenting higher surface area and microporosity than BC of woody origin.

Reclamation practices following open-pit mining typically include the reconstruction of soil-like profiles using a combination of native soil materials, industrial by-products, and fertilizers. Our overall objective was to compare the quality of eight soil materials used during reclamation in the Athabasca oil sands region of western Canada by characterizing their microbial communities as well as their response to a range of fertilization treatments. Materials included two carbon-rich surface soil materials, four B horizons with varying extractable phosphorus and pH, the parent geological material (PGM), and tailings sands (TSS), a by-product of oil extraction. Measured indices of microbial activity included the activities of b-glucosidase, acid phosphatase, and phenol oxidase. Total biomass and structure of the soil microbial community were characterized based on phospholipid fatty acid (PLFA) analysis. Soil materials and fertilization treatments were tested with multivariate regression trees and non-metric multidimensional scaling. Material type, rather than fertilization level, had the largest impact on all microbial parameters, including biomass, activity, and composition. Only the nutrient-poor materials (PGM, TSS, and one of the B horizons) showed a response to fertilization. The microbial composition of three of the four B horizons was more similar to the two carbon-rich surface soil materials than it was to PGM or TSS. Hence, we propose that these subsoil materials present an advantage over the use of the underlying PGM when reconstructing upland sandy soils. Finally, results indicated that soil microbial biomass could be used as a good indicator of seedling growth when no fertilizer was applied.

Fire is the dominant natural disturbance regime in most ecosystems of California. The long-term relict of fire is charcoal, which has been shown to increase N mineralization and also represents a pool of chemically stabilized C whose quantity and spatial distribution have not been well characterized in forest soils. We examined the charcoal content in three different ecosystems of the Sierra Nevada, including oak woodland (low elevation), mixed conifer (middle elevation), and red fir (high elevation). Using a fine-scale (2.5-m minimum resolution) spatially explicit sampling protocol applied to plots ranging between 0.25 to 0.5 ha, we examined the autocorrelation of forest floor and mineral soil properties including charcoal C. Charcoal C content ranged from 1000 to 5000 kg ha -1 in the surface 6 cm of soil and increased with increasing elevation and latitude. Spatial patterns of forest floor and mineral soil properties were generally patchy at a scale of 5 to 20 m, except in the mixed conifer ecosystem (no pattern). The patchiness that existed at the other sites was largely a result of the distribution of total C and total N in the mineral soil. A spatial mixed-effect ANOVA indicated that charcoal had a 10 to 20% effect on C and N contents in both forest floor and mineral soil surface horizons, independent of other parameters including ecosystem type and total C or N. These results provide evidence that charcoal has a relationship with soil C and N content, which may influence soil biogeochemistry.

Soil microorganisms have numerous functional roles in forest ecosystems, including: serving as sources and sinks of key nutrients and catalysts of nutrient transformations; acting as engineers and maintainers of soil structure; and forming mutualistic relationships with roots that improve plant fitness. Although both prescribed and wildland fires are common in temperate forests of North America, few studies have addressed the long-term influence of such disturbances on the soil microflora in these ecosystems. Fire alters the soil microbial community structure in the short-term primarily through heat-induced microbial mortality. Over the long-term, fire may modify soil communities by altering plant community composition via plant-induced changes in the soil environment. In this review, we summarize and synthesize the various studies that have assessed the effects of fire on forest soil microorganisms, emphasizing the mechanisms by which fire impacts these vital ecosystem engineers. The examples used in this paper are derived primarily from studies of ponderosa pine-dominated forests of the Inland West of the USA; these forests have some of the shortest historical fire-return intervals of any forest type, and thus the evolutionary role of fire in shaping these forests is likely the strongest. We argue that the short-term effects of fire on soil microflora and the processes they catalyze are transient, and suggest that more research be devoted to linking long-term plant community responses with those of the mutually dependent soil microflora.

Fire in boreal ecosystems is known to affect CO2 efflux from forest soils, which is commonly termed soil respiration (Rs). However, there is limited information on how fire and recovery from this disturbance affects spatial variation in Rs. The main objective of this study was to quantify the spatial variability of Rs over the growing season in a boreal aspen (Populus tremuloides Michx.) fire chronosequence. The chronosequence included three stands in northern Alberta; a post fire stand (1 year old, PF), a stand at canopy closure (9 years old, CC), and a mature stand (72 years old, MA). Soil respiration, temperature and moisture were measured monthly from May to August using an intensive spatial sampling protocol (n = 42, minimum lag = 2 m). Key aboveground and belowground properties were measured one time at each sampling point. No spatial structure was detected in Rs of the PF stand during the peak growing season (June and July), whereas Rs was auto-correlated at a scale of < 6 m in the CC and MA stands. The PF stand had the lowest mean Rs (4.60 μmol C m-2 s-1) followed by the CC (5.41 μmol C m-2 s-1), and the MA (7.32 μmol C m-2 s-1) stand. Forest floor depth was the only aboveground factor that influenced the spatial pattern of Rs in all three stands and was strongest in the PF stand. Enzyme activity and fine root biomass, on the other hand, were the significant belowground factors driving the spatial pattern of Rs in the CC and MA stands. Persistent joint aboveground and belowground control on Rs in the CC and MA stands indicates a tight spatial coupling, which was not observed in the PF stand. Overall, the current study suggests that fire in the boreal aspen ecosystem alters the spatial structure of Rs and that fine scale heterogeneity develops quickly as stands reach the canopy closure phase (