Abstract
The success of oil sands reclamation can be impacted by soil salinity depending on the materials used for soil reconstruction and the capping strategies applied. Using both a greenhouse-based column experiment and numerical modeling, we examined the potential pathways of salt migration from saline groundwater into the rooting zone under different capping strategies (the type and the thickness of the barrier layer) and water balance scenarios. The experimental results showed that there would be salinity issues in the cover soil within several growing seasons if there was a shallow saline groundwater table and if the soil was not properly reconstructed. The thickness of the barrier layer was the most significant factor affecting the upward movement of saline groundwater and salt accumulation in the cover soil. The suitable thickness of the barrier layer for preventing the upward movement of saline groundwater and salt accumulation in the cover soil for each material varied. A numerical simulation for a 15-year period further indicates that, when the cover soil was 50 cm of peat-mineral soil mix and when wet, dry, or normal climatic conditions were considered, the minimum barrier thickness to restrain salt intrusion into the cover soil in the long term was about 75 or 200 cm for coarse tailings sand or overburden barrier material, respectively. In view of the above, to minimize salt migration into the rooting zone and ensure normal plant growth, oil sands reclamation should consider salt migration when designing soil capping strategies.
Highlights
In the Athabasca Oil Sands Region (AOSR) of Canada, surface mining for oil sands have completely altered the landscape from boreal forests and wetlands into mine pits, dumps, and tailings ponds.By 2017, the disturbed lands already covered an area of 895 km2, which account for about 0.2% of Alberta’s boreal forest [1]
A better understanding of salt migration under different capping strategies and different hydrologic conditions will help develop better land reclamation practices to deal with soil salinity
This paper examined the potential pathways of salt migration into the rooting zone to affect plants using a greenhouse-based column experiment and numerical simulation, and tried to address three key questions: (1) how does the texture of the barrier material affect salt movement? (2)
Summary
In the Athabasca Oil Sands Region (AOSR) of Canada, surface mining for oil sands have completely altered the landscape from boreal forests and wetlands into mine pits, dumps, and tailings ponds. The major waste materials requiring capping in oil sands reclamation are coarse tailings sand and overburden. Soils are considered “unsuitable” for plants when the electrical conductivity (EC) reaches or exceeds 8 dS/m [6] At these high salinity levels, the physiological functions of most boreal forest species would be restricted, and result in a failure of the reclaimed lands to meet the capability requirements [7]. Fine-textured overburden has strong water holding capacity but weak infiltration ability It preserves moisture and promotes plant growth but creates the risk of salinization due to capillarity. A better understanding of salt migration under different capping strategies and different hydrologic conditions will help develop better land reclamation practices to deal with soil salinity. What thickness of the barrier material will minimize salt intrusion into the rooting zone in reconstructed soils in the presence of a shallow saline groundwater table? What thickness of the barrier material will minimize salt intrusion into the rooting zone in reconstructed soils in the presence of a shallow saline groundwater table? and (3) how does water balance affect salt movement in reconstructed soil profiles?
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