The Athabasca oil sands of northern Alberta produce approximately 25% of Canada's annual oil production. However, it also produces approximately lo5 m3/dayof tailings containing naphthenic acids, unrecovered oil, and salts. These tailings are toxic to fish and amphibians. The toxicity is believed to be the result of the naphthenic acids, a diverse group of saturated, cyclic carboxylic acids. Microbial communities found in wetland sediments receiving processwater are known to degrade naphthenic acids and this study aimed to examine the degrading ability of these communities and simultaneously examine their relatedness using physiological and genetic measures. Twelve wetlands were sampled a total of six times over two years, including three controls located off the mine sites, and 9 others located on a mine site and affected by processwater to varying degrees. The ability to degrade naphthenic acids was examined by monitoring the evolution of I4c02from microcosms to which I4c-labelled surrogates cyclohexane carboxylic acid (CCA) or decahydronaphthenic acid (DHNA) were added. Sole-carbon-source utilization was examined using
BIOLOG Eco-Plates. Denaturing gradient gel electrophoresis (DGGE) was performed on DNA extracted directly from the sediment and amplified using 16s rDNA primers. The CCA and BIOLOG results were similarily affected by seasonal trends and did not correlate with the concentrations of naphthenic acids and oil. The degradation of DHNA and the DGGE results both correlated with naphthenic acid and oil concentrations found in the wetlands. The control wetlands exhibited little ability to degrade DHNA, and clustered together when analyzed by DGGE. All the on-site wetlands could degrade DHNA and had similar DGGE profiles, even those with only low concentrations of naphthenic acids. The DGGE profiles from replicates within a wetland at a particular time were almost always identical for processwater affected wetlands, suggesting that the communities found there were strongly influenced by environmental factors, especially naphthenic acids. This study found that microbial communities are strongly affected by even low levels of naphthenic acids and that a community's status was best examined using degradation of DHNA and DGGE.