To better elucidate the ecological effects of naphthenic acids and major ions liberated in oil sands development, the summer-time composition of phytoplankton communities in ten water bodies near Fort McMurray (northeastern Alberta) was studied in 1997. The water bodies varied in degree of process water influence, and in age, size and ancillary chemical characteristics. Community biomass of phytoplankton was not systematically related to naphthenic acid or major ion concentrations, even though the higher naphthenate concentrations exceeded published EC50’s for acute effects on several different aquatic species. Chlorophyta were frequently dominant, particularly where naphthenate and major ion concentrations were highest. Canonical Correspondence Analysis (CCA) revealed gradients in taxonomic composition at a finer (genus and species) taxonomic level. Despite the simultaneous and uncontrolled variation of other environmental factors, naphthenate and major ion concentrations (as indexed by conductivity) explained a highly-significant 40% of the variation in taxonomic composition. Systems with naphthenates < 6.5 mg 1-1 and conductivity < 800 ΦS cm-1 were clustered together near the origin of the CCA plots, suggesting little ecological effect at such concentrations. Taxa associated with elevated naphthenate and/or major ion concentrations were derived from six different algal divisions and included many that were identified as tolerant in previous bioassay experiments. Over the range of concentrations encountered (1.5–45 and 100–3000 mg 1-1 for naphthenates and ions, respectively), CCA indicated that the ecological effect of major ions appeared to be at least as great as that of naphthenates.

Introduction

Production of crude oil from the Athasbaca oil sands formation is a large and growing industry centered in northeastern Alberta, Canada. At present, crude oil production from oil sands account for more than 25% of Canada’s annual oil production, and within 5 years this is expected to rise to over 50%. Currently, most of this production is based on a caustic hot-water extraction method, which results in the production of large volumes of fluid tailings (FTFC, 1995; Mikula et al., 1996). The fines fractions of these tailings are stored as an aqueous suspension (clays and silts, residual bitumen and water, with elevated dissolved organic and inorganic components) in large settling basins, where they undergo a de-watering process and slowly densify. The released water from this process is recycled back to the operation. With time, the fine tails will densify to more than 1.25 t/m³, at which point it is referred to as mature fine tails (MFT). Even at this stage, the MFT consist of more than 80% water byvolume Fine Tailings Fundamentals Consortium (FTFC, 1995). As a result of leaching from the ore, addition of process chemicals, and the recycling of waters, there has been and will continue to be an increase in the levels of salts and dissolved organics in the process-affected waters (Mikula et al., 1996). The impacts on water quality will be further influenced by the application of new tailings management technologies, such as composite or consolidated tails (CT). In the CT process, inorganic coagulant aids (i.e. gypsum) are added to tailings mixtures at dosages sufficient to initiate the coagulation of clays, which remain with the coarser sand fractions during deposition (Matthews et al., 2000). However, the increase in salinity of the resulting released waters will be elevated (MacKinnon et al., 2000).