Reclaiming to Brackish Wetlands in the Alberta Oil Sands: Comparison of Responses to Sodium Concentrations by Carex atherodes and Carex aquatilis

The variation in sodium concentrations in waters of natural fens and marshes on the western Canadian landscape provides a background for choosing the appropriate plants for wetland reclamation. Broad tolerances to salinity are especially important for reclamation trials on saline-rich ‘in-pits’ that were left from open-pit oil sands mining. One such species, Carex aquatilis, has been identified as a key species in early reclamation attempts; however, at the Sandhill Wetland on the Syncrude Canada oil sands lease, this species has aggressively colonized, dominating parts of the wetland and limiting species diversity. A second species, also widespread on natural lake shores and marshes, is Carex atherodes, with field observations suggesting a broad tolerance to salinity. Here, we examine the responses of this species to a series of sodium concentrations and compare these to those of C. aquatilis. In particular, we addressed three questions: (1) How do structural attributes of C. atherodes respond to a series of Na+ concentration treatments? (2) Are different structural responses related to the functional attributes of photosynthesis, stomatal conductance, and/or transpiration rate? (3) How do these responses compare to those of C. aquatilis? We implemented a phytotron experiment to test the responses of these two species to either five or six concentrations of sodium, ranging from 20 to 3000 mg Na+ L−1. In general, structural responses of C. atherodes did not differ between 50 and 789 mg Na+ L−1, while performances of all attributes were reduced at 1407 mg L−1. Physiological attributes had high variation, but also had reduced performances at similar treatment levels. In comparison, a clear threshold was present for structural attributes in Carex aquatilis between 1650 and 2148 mg Na+ L−1, while physiological attributes were reduced between 1035 to 1650 mg Na+ L−1. These responses from C. aquatilis were similar to those previously reported. Na+ concentrations in porewater at the Sandhill Wetland in 2019 reached as high as 1200 mg Na+ L−1, with natural subsaline and sodic sites ranging much higher. Although all of the plants in the treatments remained viable at the end of the experiment, these results indicate that Na+ concentrations above 1500–2000 mg Na+ L−1 may inhibit the growth of these two species and decrease their competitive abilities.

Effects of seasonal weathering on dewatering and strength of an oil sands tailings deposit

Considerable research has been conducted over the past decade by oil sands mining companies to improve the dewatering and strength properties of fluid fine tailings deposits in an effort to meet the regulatory and closure requirements. Commercially employed dewatering treatment technologies (inline flocculation, thickening, and centrifugation) may not be sufficient to develop the strength for the creation of trafficable landscape without the use of soft soil capping technologies. These treated tailings are continuously deposited creating soft and saturated deep deposits. Seasonal weathering may be an additional promising technology to further dewater the treated tailings and promote the development of shear strength at the surface. The effects of seasonal weathering on dewatering and strength were investigated in this paper by performing multiple cycles of freeze-thaw and alternate drying-wetting cycles on two types of treated tailings deposit. The results indicate that multiple cycles of seasonal weathering significantly increased the dewatering and strength properties. However, different parameters such as freezing gradient, number of seasonal cycles, and pore water chemistry play an influential role in changing the magnitude of the strength. The results also suggest that a minimum threshold strength value is required where the effects of rainfall rewetting had a minimal impact on strength reduction (the strength corresponding to the moisture content approaching the plastic limit).

The Appropriateness of Using Aquatic Snails as Bioindicators of Toxicity for Oil Sands Process-Affected Water

Canada’s oil sands mining activity produces large volumes of oil sands process-affected water (OSPW), and there have been increasing concerns regarding the potential environmental impacts associated with this material. Developing an understanding of the toxicity of OSPW is critical to anticipating and mitigating the potential risks and effects of the oil sands industry on surrounding ecosystems. The composition of OSPW is highly variable and is influenced by a range of factors. While numerous research projects have been conducted on the toxicity of OSPW, much remains unknown about its impact on various biota. Freshwater gastropods (snails and slugs) are an ecologically crucial aquatic group, and members of this taxa have been used as bioindicators in a range of ecological settings. The literature suggests freshwater snails could be used as an indicator of toxicity in monitoring programs associated with oil sands development. This mini-review explores the use of snails as bioindicators in aquatic systems affected by oil sands development, focusing on how snails may respond to potential constituents of concern in systems exposed to OSPW.

Seed germination in tailings cake and cake-reclamation substrate mixtures with oil sands process water

We investigated the germination of 13 species commonly used in oil sands mining reclamation of boreal forest as influenced by substrate type (potting soil, tailings cake and mixtures of cake-sand, cake-peat and cake-forest floor mineral mix (FFMM)) and water quality (0, 50 and 100% oil sands process water). Germination responses clustered into three groups with trees and graminoids exhibiting the highest germination (84-99%), followed by shrubs and forbs with intermediate germination (46-69%), and the native forb species, Chamerion angustifolium, Achillea millefolium and Galium boreale, with the lowest germination (7-18%). Among substrates, potting soil supported the highest germination (69%), followed by cake mixed with peat (64%) or FFMM (63%), cake-sand (60%) and cake (57%). Concentrations of ions, e.g. sodium and chloride, were higher in cake and cake-sand than in cake-peat or cake-FFMM suggesting that mixing cake with FFMM or peat can alleviate salt stress and encourage germination. Process water had little or no effect on germination especially on cake and cake amendments possibly due to the high ionic content of these substrates. There were major differences in germination response among species. Trees and graminoids may be well suited for reclaiming oil sands tailings whereas native forbs may perform poorly when used for revegetating tailings.

Growth Response of Aspen and Alder to Fresh and Stockpiled Reclamation Soils

Soil stockpiling is a common reclamation practice used in oil sands mining in the boreal forest region of Canada to conserve soil resources; but stockpiling may have detrimental effects on soil quality and plant growth. We examined growth response of trembling aspen (Populus tremuloides Michx.), a fast-growing early successional tree, and green alder (Alnus viridis (Chaix) DC. ssp crispa (Ait.) Turrill), a nitrogen-fixing shrub, to stockpiling and fertilization treatments on two reclamation soils (forest floor mineral mix (FFMM) and peat mineral mix (PMM)). Aspen and alder seeds were planted and their growth monitored for four months in the greenhouse. We found that unfertilized stockpiled FFMM supported significantly higher aspen and alder aboveground biomass than the other fresh and stockpiled soils. Phosphorus and potassium supply rates were highest in stockpiled FFMM and were positively correlated with aboveground plant biomass. There was no significant difference in aspen and alder aboveground biomasses between unfertilized fresh FFMM and PMM soils. Aspen grown in combination with nitrogen-fixing alder did not experience competition or facilitation except on fresh PMM, where aspen height declined. Fertilization increased both aspen and alder growth and eliminated differences in growth between soil types and stockpiling treatments. Our study showed that individual soil properties are more important for revegetation purposes than type of soil or stockpiling treatment.