Tailings are the waste produced as a result of the extraction of oil from the tar sands in northern Alberta. Many avenues for the reclamation of tailings are being researched, but one area that has received little attention is phytoremediation. The Alder-Frankia symbiotic relationship in the tailings was investigated for its potential in revegetation and remediation of the tailings. Two species of alders were examined Alnus glutinosa and A. rugosa . The impact of the alders was monitored through the investigation of the differences in the microbial community present in the oil sands tailings and composite tailings (CT) with and without alders. For our investigation we used culture dependent techniques (plate counts and mineralization assays) and culture independent techniques (16S rRNA gene PCR, catabolic PCR and DGGE). The alders lowered the pH of the tailings, increased rates of mineralization, increased the general microbial population in the tailings by one to two orders of magnitude and increased the microbial diversity.

A. rugosa however, had a greater impact on the mineralization of poly aromatic hydrocarbons (PAHs) and, being native to Alberta, was chosen for further experimentation, using only composite tailings. The aim of the experiments was to determine the effect of a Frankia inoculum on the growth of A. rugosa in (CT) and the associated microbial community. The microflora in the bulk soil, rhizosphere and inside the root of inoculated and non-inoculated A. rugosa were compared through microbial enumerations of the community, with general and selective media and mineralization assays. A. rugosa inoculated with Frankia was taller and the roots were more developed and the endophytic community of inoculated A. rugosa had greater rates of naphthalene mineralization.

The results indicate that A. rugosa inoculated with Frankia could be used for the phytoremediation of tailings and for the re-establishment of a forest ecosystem.