Buried wood effects on soil nutrient supply and microbial activity in different oil sands reclamation soils in Northern Alberta
Manchola Rojas, L. A. . 2022.
Abstract
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.