Lessons in establishing plant communities on constructed fens for oil sands mine reclamation
Date
2018
Authors
Borkenhagen, Andrea, author
Cooper, David J., advisor
Paschke, Mark, committee member
Vitt, Dale, committee member
Smith, Melinda, committee member
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Abstract
The third-largest proven oil deposit in the world is in Alberta, underlying 142,000 square kilometers of Canada’s boreal covered by forested uplands and peatland basins. The vast deposit is in the form of oil sands that consist of a mixture of sand, water, clay and oil. Where oil sands are near surface, they are excavated in open-pit mines that remove the overburden landscape to extract the resource. Reclamation is a legislative condition for oil sands operators to replace ecosystems that are lost. This involves recontouring the surface to recreate landscape processes and introducing plant species common in regional reference sites. Fen peatlands are the most dominant ecosystem type but provincial standards have allowed compensation with marsh wetland as they are easier to create. Oil sands extraction and reclamation is highly controversial with opponents suggesting that destroyed peatlands will not be restored. Scientists, operators and regulators are more aware that peatland reclamation is critical and despite the constraints, research is underway in two reclamation fens that have recently been constructed. To effectively reclaim fens, we need to understand how plant species and communities respond to environmental gradients, the most effective methods to introduce species, and which success criteria are achievable. In the following chapters, I examine drivers of plant community assembly in natural and reclaimed fens and consequences of abiotic, biotic, and construction constraints on ecosystem structure and function. A major constraint in fen reclamation is achieving optimal surface topography and seasonal water table position to support desired plants. Moss-dominated fens are the most common regional peatland type and evaluating the response of mosses to submergence in natural fens provides insight into species selection and processes of recovery for reclaimed fens. I conducted a field experiment to determine the short and long-term tolerances of four fen mosses to submergence from 1 to 8 weeks. I found that moss species vary in their responses to submergence duration and that shifts in community composition that support tolerant dominant species such as Tomentypnum nitens increased moss community resilience and provide stability in boreal fen ecosystems. As part of a multi-stakeholder collaboration, the first self-sustaining reclamation fen and associated watershed was constructed within an oil sands mine site north of Fort McMurray, Alberta. To determine the most effective approach to establish fen plants, I designed and implemented a large-scale multifactorial field experiment that tested introducing moss layer transfer material (MLT), seeds, and seedlings under wood-strand mulch and with a Typha latifolia weeding treatment. Four years after planting, the MLT and Juncus balticus seedling treatment supported the highest fen bryophyte and vascular plant cover and species richness. Weeding did reduce T. latifolia cover but was not necessary in areas where seedlings or MLT was introduced. The most successful fen species to establish was C. aquatilis, which rapidly colonized but also reduced cover and richness of bryophytes and other vascular plants. To provide a broader context, I examined vegetation establishment across the two reclaimed fens that had different water level gradients and species introduction approaches. Despite differences, peat-accumulating bryophyte and vascular plant communities developed in both fens. Community convergence occurred due to dominance of C. aquatilis, and community divergence occurred in response to water level gradients. Dominant species adapted to site conditions can be introduce by basic approaches such as seeding. Intensive approaches such as planting seedlings or spreading MLT should be prioritized in areas of overlap along water level gradients between desirable and undesirable communities to deter establishment of non-peat forming species. Bryophyte cover and desirable species richness was highest following intensive approaches and where the summer water level was -10 cm to -40 cm from the soil surface. My research shows that it is possible to reclaim peat-accumulating bryophyte and vascular plant communities in the post-mining landscape of Alberta and that a range of successful outcomes are achievable. Previous assertions that fens cannot be reclaimed after mining activities are antiquated as large-scale construction designs and species introduction approaches are actively underway and the results are proven.
Description
Rights Access
Subject
boreal
oil sands
Alberta
reclamation
moss