Direct Evaluation of in Situ Biodegradation in Athabasca Oil Sands Tailings Ponds Using Natural Abundance Radiocarbon

Abstract

Compound-specific stable (δ(13)C) and radiocarbon (Δ(14)C) isotopes of phospholipid fatty acids (PLFAs) were used to evaluate carbon sources utilized by the active microbial populations in surface sediments from Athabasca oil sands tailings ponds. Algal-specific PLFAs were absent at three of the four sites investigated, and δ(13)CPLFA values were generally within ~3‰ of that reported for oil sands bitumen (~-30‰), suggesting that the microbial communities growing on petroleum constituents were dominated by aerobic heterotrophs. Δ(14)CPLFA values ranged from -906 to -586‰ and pointed to significant uptake of fossil carbon, particularly in PLFAs (e.g., cy17:0 and cy19:0) often associated with petroleum hydrocarbon degrading bacteria. The comparatively heavier Δ(14)C values found in other, less specific PLFAs (e.g., 16:0) indicated the preferential uptake of younger organic matter by the general microbial population. Since the main carbon pools in tailings sediment were essentially "radiocarbon dead" (i.e., Δ(14)C ~ -1000‰), the principal source for this relatively modern carbon is considered to be the Athabasca River, which provides the bulk of the water used in the bitumen extraction process. The preferential utilization of the minor amount of younger and presumably more labile material present in systems otherwise dominated by petroleum carbon has important implications for remediation strategies, since it implies that organic contaminants may persist long after reclamation has begun. Alternatively, this young organic matter could play a vital and necessary role in supporting the microbial utilization of fossil carbon via cometabolism or priming processes.

Sequential bioavailability of sedimentary organic matter to heterotrophic bacteria

“…Thus, it is difficult to distinguish between organic matter pools that support the growth of heterotrophic bacteria and those that do not. Natural abundance stable ( 13 C) and radiocarbon ( 14 C) analyses have become powerful tools for probing the sources and ages of natural organic matter consumed by microbes (Petsch et al, 2001;Wakeham et al, 2006;Pearson et al, 2008;Ahad and Pakdel, 2013;Mailloux et al, 2013;Mahmoudi et al, 2013a,b). Heterotrophic microorganisms carry the same 14 C signatures and nearly the same 13 C signatures as their carbon sources; therefore, the 13 C and 14 C signatures of both microbial cellular components (e.g.…”

Stimulation of Microbially Mediated Arsenic Release in Bangladesh Aquifers by Young Carbon Indicated by Radiocarbon Analysis of Sedimentary Bacterial Lipids

“…58 This approach has been used to identify microbial carbon sources in a number of environments 40,46–57 including contaminated soils, 52 coastal environments, 48,51,56 and ground-water systems. 55,59 …”

Nutritional support of inland aquatic food webs by aged carbon and organic matter

“…It is well-documented that heterotrophic bacteria play an important role in the degradation and utilization of fossil aged petroleum hydrocarbons in many aquatic systems (Atlas 1981;Heitkamp and Johnson 1984;Ahad and Pakdel 2013). Bacteria, through their enzymatic and hydrolytic activities, are also known to mediate the mobilization of C and OM to inland waters (Guillemette et al 2016).…”