Characterizing the Organic Composition of Snow and Surface Water in the Athabasca Region

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  • This pilot study was conducted by Alberta Innovates – Technology Futures (AITF) to characterize the composition of organics present in snow and surface waters in the Athabasca Oil Sands Region (AOSR) with the goal of identifying whether atmospherically-derived organics present in snow are a significant contributor to the organics detected in rivers and lakes in the region. This study is divided into two parts, each describing a different approach to characterizing the organics present in snow and surface waters. In Part 1, we interpret existing polycyclic aromatic hydrocarbon (PAH) concentration data, collected from various monitoring programs in 2011, to compare the composition of PAHs in snow and surface waters across the AOSR. In Part 2, we interpret new ultra-high resolution mass spectrometry analyses of snow and surface water samples collected in 2012 to compare the dissolved polar organics present in snow and surface waters in the Athabasca Oil Sands region (AOSR). The first approach applied in this study uses existing data from snow, river and lake monitoring programs conducted during 2011 which measured total (dissolved + particulate) PAH concentrations in snow and surface waters in the region. The 2011 dataset includes total (dissolved + particulate) concentrations for 34 parent and alkylated PAH species for 105 snow, 272 Athabasca River and tributary, and 3 lake samples. These data were compiled so that the composition of PAHs in the Athabasca River, its tributaries and a small number of lakes could be compared with that of snowmelt. The snow data show compositional differences between the PAHs present in snow sampled from areas closest to oil sands activities (i.e., near-field sites) and from more distant (i.e., far-field) snow sampling locations. Despite large concentration variations in snow along geographic gradients, the composition of PAHs are found to be similar among near-field sites, but change significantly at far-field sites. Both the near- and far-field snow samples have PAH compositions that are different from the PAHs present in the Athabasca River, its tributaries and lakes. Compositional differences in PAH assemblages are also evident between tributaries and the Athabasca River. PAH concentrations in rivers are found to vary seasonally, with peak concentrations observed in July 2011 when Athabasca River levels were at their highest. However, the composition of PAHs present in July 2011 do not resemble the composition of PAHs identified in snow, suggesting that direct transfer of PAHs accumulated on snow from atmospheric deposition to Athabasca River and its tributaries in the area is not a major source of PAHs present in surface waters. The timing of peak PAH concentrations in rivers, which coincides with a high flow period during freshet, does suggest that snowmelt may contribute indirectly to increases in PAH concentrations due to processes such as increased catchment runoff, erosion of stream channels, and snowmelt-induced groundwater inputs during this dynamic hydrologic period. The second approach applied in this study uses Electrospray Ionization Fourier Transform Mass Spectrometry (ESI-FTICR MS) to characterize the dissolved polar organic composition of snow and surface water samples provided by various Alberta Environment and Sustainable Resource Development (AESRD) programs conducted in 2012. The 2012 samples analyzed by ESI-FTICR MS include 7 snow samples, 73 Athabasca River and tributary samples, and 6 lake samples. This profiling method identified thousands of dissolved polar compounds including the acidic organic components in negatively charged ESI(-) mode, and basic components in positively-charged ESI(+) mode. Although based on a limited number of samples, the organic profiles obtained for the snow samples in ESI(-) mode show compositional differences in the dissolved organics present in snow sampled from sites closest to oil sands activities (<5 km) and those sampled from more distant locations. There are also very significant compositional differences between the dissolved polar organics present in snow and surface waters in the AOSR. The composition of dissolved organics present in the Athabasca River upstream of the AOSR (i.e., Athabasca River at Athabasca) are found to be different from samples obtained from downstream sites in the vicinity of AOSR (i.e., Athabasca River at Fort McMurray and Athabasca River at Firebag confluence). The upstream Athabasca River sites tend to share some compositional similarities with far-field snow deposition, while the downstream Athabasca River sites are more similar to local tributaries. This contrast likely indicates shifts in the relative importance of regional snowmelt versus local inputs from small tributaries. The results of these two separate approaches, which characterized different components of the organics present in snow and surface waters in the AOSR, leads to some similar conclusions. Both show compositional differences between the organics present in the snowpack near the centre of oil sands activities compared with more far-field locations and between the Athabasca River and its tributaries. The compositional differences between organics present in snow and those sampled in surface waters in the region suggest that even though the spring freshet is a period when elevated PAHs have been found in the Athabasca River the organics released directly from snow are not the dominant inputs during this peak discharge. These compositional differences may be useful tools for differentiating air-borne vs. water-borne organics away from the AOSR. The two methods used show the usefulness of PAH composition (i.e., relative concentrations of PAHs) and polar organic profiling in differentiating sources of organics in the region. The role of potential transformations of PAH and ESI-FTICR MS composition profiles during spring melt and during interactions along typical surface and subsurface flowpaths within wetland-dominated catchment areas typical of the region remains to be better understood.

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    Attribution 3.0 International