Introduction
The Athabaska region in northern Alberta, Canada is home to one the largest oil sands deposits on earth (Larter & Head, 2014). The process of removing the bitumen from the sand produces a form of waste known as fluid fine tailings, which is composed primarily of small mineral particles and water. The tailings contain inorganic salts as well as toxic organic compounds such as naphthenic acids (Foght et al., 2017). Tailings material can have high salinity which can result in inhibited water uptake and reduction in plant growth (Apostol et al., 2004). Although there is still a lack of understanding on how naphthenic acids impact plants, some studies suggest they can be toxic to plants and also to a vast array of other flora and fauna (Brown & Ulrich, 2015). It is estimated that the Athabaska oil sands region of Alberta has produced roughly 1 billion m3 of mine tailings to date (Burkus, Wheler and Pletcher 2014). For this reason oil companies have been attempting to find a way to re-use the tailings in the reclamation process, as subsoils for constructed wetlands and end pit lakes (Brown & Ulrich, 2015).
The problem is that we do not have a good understanding of what happens to tree growth when tailing is used as a subsoil material. To better understand the impacts of using fine tailings material as a subsoil substrate, a greenhouse study was conducted to evaluate how Beaked willow (Salix bebbiana) would grow in such a substrate. The fine tailings material was used as the subsoil in long pots, and various soil types (forest floor mineral mix, peat mineral mix, 50/50 mix of peat and forest floor) were used as the top soil, at varying capping depths. The research questions being asked are: 1- what impact does a capping depth have on plant growth, when placed above fine tailings material; 2- which soil works best for plant growth on fine tailings; 3-does adding biochar to the capping material improve growth? My first hypothesis is that capping depths will have a positive correlation with plant growth, as the negative impacts of the tailings (such as naphthenic acids) will be further from the root zone in early development. My second hypothesis is that the 50/50 mix will combine the positive soil properties from both soils (water retention from peat and mineral richness from forest floor) to produce the best medium for plant growth. My third hypothesis is that biochar will reduce some of the negative effects of the tailings, by absorbing/adsorbing the toxic components in the tailings, such as the naphthenic acids and salts, thus producing better plant growth. However, due to the short nature of the experiment, there is a chance that no effect will be seen as a result of the biochar amendment.
These findings could impact land reclamation management decisions in the oil-sand industry. If tailings are going to be used for reclamation purposes, it’s important to understand the impact they may have on plant growth, the soil and the environment.
The problem is that we do not have a good understanding of what happens to tree growth when tailing is used as a subsoil material. To better understand the impacts of using fine tailings material as a subsoil substrate, a greenhouse study was conducted to evaluate how Beaked willow (Salix bebbiana) would grow in such a substrate. The fine tailings material was used as the subsoil in long pots, and various soil types (forest floor mineral mix, peat mineral mix, 50/50 mix of peat and forest floor) were used as the top soil, at varying capping depths. The research questions being asked are: 1- what impact does a capping depth have on plant growth, when placed above fine tailings material; 2- which soil works best for plant growth on fine tailings; 3-does adding biochar to the capping material improve growth? My first hypothesis is that capping depths will have a positive correlation with plant growth, as the negative impacts of the tailings (such as naphthenic acids) will be further from the root zone in early development. My second hypothesis is that the 50/50 mix will combine the positive soil properties from both soils (water retention from peat and mineral richness from forest floor) to produce the best medium for plant growth. My third hypothesis is that biochar will reduce some of the negative effects of the tailings, by absorbing/adsorbing the toxic components in the tailings, such as the naphthenic acids and salts, thus producing better plant growth. However, due to the short nature of the experiment, there is a chance that no effect will be seen as a result of the biochar amendment.
These findings could impact land reclamation management decisions in the oil-sand industry. If tailings are going to be used for reclamation purposes, it’s important to understand the impact they may have on plant growth, the soil and the environment.
Figure 4. Oil-sand production process. Source: https://www.oilsandsmagazine.com/technical/mining/water-management