Abstract

Thecamoebian (testate amoebae) assemblages in samples collected in August 2007 and June 2008 from Suncor Energy Inc. Constructed Wetlands Test Facility, Fort McMurray, Alberta were found to respond to varying levels of oil sands process-affected water/materials (OSPW/OSPM). Oil sands process affected material is characterized by elevated conductivity and naphthenic acid concentrations, and a strong relationship was found between thecamoebian assemblages and both of these impact-indicator constituents (r2 = 0.707 and r2 = 0.743, respectively). Wetlands highly impacted by OSPM contained low-diversity assemblages dominated by centropyxid thecamoebians (Centropyxis aculeata and C. constricta) and Arcella vulgaris. Less-impacted sites, in contrast, had higher relative abundance and more-diverse assemblages dominated by difflugiid thecamoebians, primarily Difflugia oblonga, D. urceolata, and Cucurbitella tricuspis. Thecamoebian assemblages responded quickly to a deliberate reduction in the rate of OSPW input to some sample sites between 2007 and 2008, with increases in species diversity and relative abundance of difflugiids. At sites with little annual change in water quality, the thecamoebian assemblages were comparable, indicating reproducibility of thecamoebians as a contamination proxy.

Canonical Correspondence Analysis (CCA) revealed the strong controls of Na/(Ca+Mg), Na/SO4, naphthenic acids, Na, alkalinity, and conductivity on the thecamoebian communities, although many of these are intercorrelated. R-mode cluster analysis emphasized the interannual similarity of the thecamoebian faunas at the same sites and the community changes at sites where the OSPW character changed. Q-mode cluster analysis showed that four main thecamoebian strains and species (Centropyxis constricta “aerophila”, Centropyxis aculeata “discoides”, Cucurbitella tricuspis, Difflugia oblonga “glans”) significantly influence assemblage composition.

The study suggests that thecamoebians are useful environmental proxies capable of gauging the impact of oil sands materials in reclaimed areas and have the potential to monitor the progression of aquatic reclamation initiatives. They also appear to be useful in gauging the success of various reclamation mitigation options, such as fertilization. The addition of nutrients resulted in higher species diversity and greater relative abundance of difflugiid thecamoebians than at a parallel site that had not been fertilized, suggesting a faster improvement in aquatic ecosystem health with nutrient loading. The rapid generation time of these protists, together with their apparent sensitivity to OSPM, make thecamoebians useful biomonitors of the progression of aquatic reclamation in oil sands operations.

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