M. Derek MacKenzie

Building a better soil for upland surface mine reclamation in northern Alberta: Admixing peat, subsoil, and peat biochar in a greenhouse study with aspen

Abstract: 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 admixtures with forest floor–mineral mix (FFM). Seedling productivity increased with admixing subsoil in both experiments with and without biochar, and there was an overall positive effect of amendment with biochar when comparing all treatments of both experiments using multivariate statistics, with biochar being more similar to FFM. Our findings suggested that peat–subsoil mixes did not provide sufficient amounts of P and Cu to seedlings. A lower K and Mn availability in peat–subsoil mixes was also identified and needs to be evaluated in further studies.

Spatial Patterns of Soil Respiration Links Above and Belowground Processes along a Boreal Aspen Fire Chronosequence

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 (<10 years).

Evaluating foliar nutrient concentration as an indicator of soil nutrients in reclaimed and natural forests in Alberta, Canada

ABSTRACT 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 Alberta, Canada, we evaluated whether trembling aspen (Populus tremuloides Michx.) foliar concentrations of macronutrients accurately represent soil solution and soil nutrient pools in both reclaimed and wildfire-impacted natural reference boreal forest ecosystems. Reclamation soils were upland-based forest soil (forest floor-mineral mix; FFMM) and lowland-based peat soil (peat-mineral mix; PMM) with and without fertilisation. Individual macronutrient concentrations differed among treatments in the soil nutrient pool, but differences decreased in the soil solution pool and disappeared in the foliar pool. Few significant correlations between foliar and belowground pools were observed, but foliar phosphorus was correlated to soil phosphorus in natural reference sites. Multivariate analyses showed reclaimed sites were different from reference sites across all nutrient pools. Again, few significant multivariate correlations between foliar and belowground nutrient pools were observed, except for the unfertilised forest floor-mineral mix site, where foliar nutrients were positively correlated with soil solution. Based on our findings, we suggest that trembling aspen foliar nutrient concentrations are not a consistently reliable indicator of soil and soil solution nutrients in reclaimed or natural ecosystems.

Biochar affects aspen seedling growth and reclaimed soil properties in the Athabasca oil sands region

Abstract: 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.