Evaluation of the Capability of Aggregated Oil Sands Mine Tailings: Biological Indicators
Authors: Li X. , Slaski J.J. , Feng Y. , Fung M. 
Published: March 2010

Abstract
An experiment was initiated in 1997 in northeast Alberta at the Syncrude Canada Ltd. Mildred Lake site to field test an innovative technique for reclamation of oil sand mine tailings. This technique was used to create an aggregated soil material from oil sand tailings. A plant community was successfully established on the soil material created by this technique. However, whether the site would be capable of supporting a self-sustainable ecosystem for the long-term remained a challenging issue. We evaluated the capability of these aggregated oil sand tailings by using biological indicators of the abundance and diversity of soil microbial biomass. Soil respiration rates and soil microbial biomass measurements were used to assess the abundance and activities of soil microbial communities. The ability of soil microbial biomass to utilize a diverse range of carbon substrates was used to assess the diversity of soil microbial communities. Soil biological activity increased with increasing growth of plant biomass and over time. Increasing the amount of peat moss or muskeg incorporated into the soil during reclamation resulted in higher organic carbon and nitrogen content and caused an increase in abundance and diversity of soil microbial biomass. These results indicate that measurements of soil respiration and substrate utilization by soil microbial communities may be used as biological indicators for assessing the capability of reclaimed soils.

Introduction
A critical component in the reclamation of oil sand tailings is to create soil materials conducive to the growth of soil microorganisms and, as a result, to stimulate the soil microbial biomass mediated nutrient cycling process following initial reclamation. Soil organic carbon dynamics is at the centre of these processes. Soil microbial biomass is largely responsible for the decomposition of soil organic matter and litters that contribute to soil nutrient pools through mineralization. Additionally, certain soil microorganisms form symbiotic associations (mycorrhizae, nodules) with plants and contribute to the overall success of plant growth. Thus the success of planting for reclamation purposes is affected by, and may be contingent upon, the quality and quantity of soil microbial communities and their activities.
This paper presents the use of a few measurements of soil microbial activities as biological indicators for evaluating the capability of reclaimed soil.

Materials and Methods
Field Site
The site, located at Syncrude Canada Ltd. Mildred Lake in northeastern Alberta, was established in 1997. Composite tailings (CT) were used as a sub-material. Five treatments were used for the top 20 cm layer. The composite tailings, amended with various amounts of peat moss, were aggregated using an aggregation technology(1). The control consisted of standard reclamation material (RM) placed over the CT base. The properties of the materials used on this site, and the treatments used, are described in Table 1.
Each of the five treatments was replicated four times. A total of 20 (10 m by 10 m) plots arranged in four blocks were set up as a randomized complete block design. After the site was established, the following tree/shrub seedlings were transplanted: