Date of Award
Doctor of Philosophy
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.
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