Impacts of Soil Stockpiling on Seed Bank Communities and the Availability of Nutrients
Buss, J.. 2020.
Abstract
Soil stockpiles are used around the world to reclaim sites affected by industrial activities.
Oil sands surface mining and in situ extraction activities in Alberta, Canada, have directly
impacted more than 900 km2 of land, with more development expected in the future. Soil
stockpiles will be essential for the reclamation of large- and small-scale oil and gas sites across
Alberta with over half of the disturbed area expected to be reclaimed using stockpiled soils.
However, stockpiling soils can lead to the degradation of soil biological, physical, and chemical
properties, so it is critical that we understand the potential implications of using this soil in
reclamation. Therefore, I studied the impacts of soil stockpiling on seed banks, aboveground
plant communities and available nutrients.
To investigate the impacts of soil stockpiling, plant communities and nutrient availability
were sampled in eight soil stockpiles of varying ages across Alberta. Four stockpiles and soils of
four nearby mature forests were sampled in the Cold Lake region (54.695 °N, 110.730 °W), and
four stockpiles and soils of two mature forests were sampled in the Fort McMurray region
(57.337 °N, 111.755 °W). Seed bank samples were taken from depths of 0-5 cm, 5-10 cm, 10-20
cm, 20-30 cm, and >50 cm and germinated in a greenhouse using the seedling emergence
method. Aboveground vegetation cover was also estimated at these locations. Soil samples were
taken from 0-10 cm, 10-20 cm, 20-30 cm, and >50 cm for a lab incubation to estimate the
availability of macronutrients (NO3-, Ca2 , Mg2 , K , H2PO4- /HPO42-, SO42-) in stockpiled and
mature forest soils using plant root simulator probes (PRS; Western Ag Innovations, Saskatoon,
SK, Canada).
n Chapter 2 the impacts of soil stockpiling were quantified by seed bank abundance,
species richness, functional group composition, and the relationships between the seed bank and
aboveground plant communities. In Chapter 3 nutrient availability was compared between
stockpiles and mature forests, as well as with depth. Nutrient availability was also compared
across stockpiles and mature forests.
The results of the seedling emergence study showed that stockpile seed banks had higher
seedling abundance and species richness than that of nearby forests but were dominated by
grasses and non-native forbs. Most seeds germinated from the surface layer, with 92% of seeds
germinating from the LFH layers in the forests, and 68% from the 0-5 cm layer in the stockpiles.
Aboveground and seed bank communities were more similar in mature forests than that expressed in stockpiles.
As indicated by the soil incubation, stockpiles had higher availability of Ca2 , Mg2 , NO3-
compared to the mature forests. There was also high availability of NO3- below 20-90 cm in
stockpiles. The variability with depth that was present in the mature forests for Ca2 , Mg2 , clay
content, and pH were not found in stockpiles, likely due to mixing. Variability was high across
stockpiles for NO3-, SO42-, and H2PO4-/ HPO42- compared to mature forests.
Planting or seeding on these stockpiles with desirable reclamation species may be useful
in the future to supplement the seed bank. Salvaging fresh topsoil to shallower depths could also
help prevent dilution of the seed bank. Variability in nutrient availability across stockpiles could
mean that management of stockpiles and reclamation sites should be done on a smaller scale and
focus on differences across stockpiles. Overall, all stockpiles were dominated by grasses and
non-native forbs, despite higher variability in N, SO42-, and H2PO4-/HPO42-.
