Organic Amendment Effects on Productivity of Wellsites Reclaimed with Suboptimal Topsoil Replacement Depth in Northeasten Alberta

Takudzwa Nawu
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Reclamation and revegetation of boreal sites disturbed by oil exploration depend on the availability
of topsoil salvaged on-site during the disturbance. For successful reclamation, current regulations
require the salvaging of enough soil to attain at least 80% of the original topsoil depth. However,
salvaged topsoil at many sites is often insufficient to achieve the 80% topsoil replacement depth
(TRD80) required for successful reclamation in western Canada. We tested organic amendment
effects on reclamation success of wellsites reclaimed with insufficient salvaged topsoil to a level
similar to the mandatory TRD80. Two main studies were conducted to examine (i) soil responses
and (ii) vegetation responses to 50% topsoil replacement depth without organic amendment
(TRD50) or amended with either peat (PTRD50) or biochar (BTRD50), relative to the TRD80
treatment, following wellsite reclamation at Cold Lake, Alberta.

Soil properties results showed that both amendments improved topsoil properties. Peat-amended
plots showed a 113% increase in total Kjeldahl nitrogen concentration relative to the mean of other
treatments, while biochar produced significantly greater potassium concentrations in TRD50
relative to peat-amended plots.

Vegetation responses to insufficient topsoil depth and organic amendment application showed an
increase in native species, graminoid and woody species richness while non-native and forb
species richness decreased across all treatments 5 yr after reclamation. Tree growth was greater in
the peat amendment and the TRD80 treatment than in the TRD50 and the biochar treatments. Peat
and biochar improved soil properties of disturbed boreal sites reclaimed with insufficient salvaged topsoil to a level suitable for successful restoration. However, in the revegetation study peat improved vegetation establishment and plant community development while biochar showed no benefits on vegetation variables. Overall, the peat treatment (PTRD50) produced similar vegetation performance results to the mandatory TRD80 treatment, indicating that peat amendment can improve reclamation success at disturbed boreal sites where salvaged soil is insufficient to achieve the optimal 80% TRD.