Characterization of key performance measures at the reclaimed sandhill wetland: Implications for achieving wetland reclamation success in the Athabasca Oil Sands.
Hartsock, J. A.. 2020. Southern Illinois University Carbondale
Abstract
Wetland reclamation efforts in the Athabasca Oil Sands Region seek to restore important
ecosystem services that were lost consequent of disturbance from oil sands mining development
in northern Alberta, Canada. Constructed on the Syncrude Canada Ltd. mineral surface lease, the
Sandhill Watershed is the first attempt to engineer a landscape capable of supporting a self-sustaining wetland above a backfilled open-pit mine. In the chapters below, through
characterization of porewater chemistry patterns, plant community structure, physical
characteristics of soil and nutrient availability the overall performance of the wetland area (the
Sandhill Wetland) is evaluated. Further, observations at the reclaimed site are compared to 12
reference wetlands (10 fens and 2 marshes) to evaluate the type of wetland to which the Sandhill
Wetland is most analogous. After six growing seasons, although water table position
management has occurred annually, the Sandhill Wetland exhibits many attributes similar to
those of the natural sites monitored. In terms of porewater chemistry, the dominant anions and
cations present in near-surface water (bicarbonate, sulfate, chloride, sodium, calcium, and
magnesium) have increased annually since the first growing season. If trends continue, the
chemical conditions at the reclamation site could be analogous to saline fens in about 7-8 years
based on projections for increasing sodium and chloride concentrations. The Sandhill Wetland
currently exhibits porewater chemistry attributes most similar to saline fens and slightly brackish
marshes. Total plant cover across the reclaimed wetland was quite high averaging 95% in the sixth growing season. Using multivariate approaches (NMDS), results show that plant
community structure across high and intermediate water table position areas are most
comparable to marshes, with Typha latifolia and Carex aquatilis exhibiting the highest cover.
Across the periphery of the site, where water table position is several centimeters below the soil
surface, plant communities are quite dissimilar from the reference sites and dominated by the
grass Calamagrostis canadensis. While sodium-tolerant species are present at the site, albeit at
low abundance, it is unclear whether long-term exposure to sodium-dominated porewaters
currently present at the Sandhill Wetland will affect performance of wetland plants that
established under low-sodium conditions. In terms of soil characteristics, clear differences were
apparent, namely, for soil bulk density patterns. Bulk density observations across all areas at the
Sandhill Wetland were higher than the reference sites and total soil carbon concentrations were
also low. These observations were expected, and as the Sandhill Wetland matures, I predict
annual production and (or) deposition of plant litter/ roots and increased biological activity will
restore near-surface soil properties in the wetland area, thereby increasing TC concentrations and
reducing soil compaction. For functional processes, using plant root simulator (PRS) probe ion
exchange membranes, results demonstrate nutrient supply across the Sandhill Wetland was most
similar to the moderate-rich and saline fens except for sulfur supply, which was considerably
elevated. Based on PRS probe and porewater observations, the Sandhill Wetland is not a
eutrophic system in the sixth growing season, and supply for most nutrients are within the ranges
of natural systems. However, effects from local atmospheric nitrogen deposition (reported up to
12 kg N ha-1 yr-1) could alter structure and function over subsequent growing seasons. Currently,
ecosystem health and functionality of the belowground environment appears to be adequately
restored at the reclamation site.
Lastly, as no officially recognized protocols exist for evaluating performance of recently
reclaimed wetlands constructed above open-pit mines, using the Sandhill Wetland as a test site I
propose a framework for evaluating reclamation site performance. Although the proposed
evaluation protocol does not rely on multivariate techniques, the performance evaluation results
support the previous findings (that were based on multivariate analysis) that a marsh-like
analogue is the most realistic reclamation outcome for the reclaimed Sandhill Wetland. While the
reclamation has been highly successful in terms of creating a wetland that has persisted, future
monitoring of water chemistry and plant community structure should continue at the Sandhill
Wetland, to capture important successional changes that may occur as the site matures.
