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Buried wood effects on soil nutrient supply and microbial activity in different oil sands reclamation soils in Northern Alberta

Manchola Rojas, L. A. . 2022.


Buried wood is an important component of natural and anthropogenic soils, yet it remains severely understudied. Nutrient immobilization as a response to wood addition in soils raises concerns from oil sands reclamation practitioners since the clear and grub procedures prior to soil salvaging tend to leave remains of unmerchantable wood that is salvaged with the soil and subsequently placed on reclamation landscapes as part of the cover soil. Additionally, there are no reports about how much buried wood is potentially added to reclamation soils in the area of Northern Alberta. This thesis aimed to investigate the impacts of buried wood on the nutrient supply and microbial communities in different soils used in oil sands reclamation and to determine how much buried wood is there in reclamation soils and how is this linked to the soil nutrient supply in the field. A 60-day incubation study was performed with different volumes and types of buried wood (0%-50%, aspen and pine wood), and four different soils (fine and coarse forest floor-mineral mix: fFFMM and cFFMM, peat-mineral mix: PMM, and Peat); analyses on soil nutrient supply rates, microbial biomass C and N, and Community Level Physiological Profiling were performed at the end of the incubation period, soil respiration was measured throughout the incubation. A complementary field study was performed in a 5-year old reclamation site with FFMM and PMM in Northern Alberta where buried wood sampling was performed and soil samples were collected for nutrient supply rate analysis. In the incubation study, responses varied depending on the soil type, but buried wood caused nitrogen immobilization in three out of the four soils at rates of 10% and above, due to an increase in the soil C:N ratio; soils with lower C:N ratio like fFFMM and PMM were more susceptible to nitrogen immobilization just after the smallest rate of 10%; buried wood increased the microbial activity but no significant changes in the soil metabolic profiles were noted. The field study concluded that the average amount of buried wood is less than 1.5% or 34 m3/ha in the top 20 cm of these cover soils and it was not linked to the soil nutrient profiles. The findings in this thesis suggest that although buried wood increases the soil C:N ratio and subsequently causes nitrogen immobilization, the amount present in reclamation soils is not a motive of concern for operational practices. However, supervision on how much buried wood is salvaged with soil is recommended to avoid nitrogen immobilization.