Composition of polycyclic aromatic compounds in river flood sediment and lake sediment cores.

<p>Bar graphs showing average composition of polycyclic aromatic compounds (PACs), expressed as relative concentration (proportion; error bars ±1 SEM) in <b>a)</b> the 2007 Athabasca Delta flood deposit and three intervals of differing flood regime at PAD 31, <b>b)</b> the 2007 Athabasca Delta flood deposit and three intervals of differing flood regime at PAD 23, and <b>c)</b> the 2007 Athabasca Delta flood deposit and two intervals that distinguish pre- and post-1967 onset of major commercial oil sands development at not flood-prone PAD 18 (note different scale of vertical axis). Names of the PAC compounds and the corresponding codes are presented along the lower expanded horizontal axis. Blue vertical bars are PACs identified by SIMPER analysis as river-transported bitumen-associated indicator compounds common in sediments deposited during flood-prone intervals (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone-0046089-t001" target="_blank">Table 1</a>). Red vertical bars are PACs identified as indicator compounds in sediments deposited during not flood-prone periods.</p

Maps of study area.

<p>Panel a): map showing locations of near-surface Athabasca oil sands exposures of the McMurray Formation (light grey), the 2009 mining footprint (dark grey) and the downstream Peace-Athabasca Delta (top center box) in northern Alberta, Canada. Top-center box in <b>a)</b> outlines area shown in Panel <b>b)</b>: Map identifying locations of the study lakes (solid circles) PAD 18 (N 58° 53.7′, W 111° 21.7′), PAD 23 (N 58° 23.5′, W 111° 26.6′) and PAD 31 (N 58° 29.6′, W 111° 31.0′) within the Peace-Athabasca Delta. Also shown are locations of the Athabasca River Cutoff (ARC) and the Embarras Breakthrough (EB). The ARC, an engineered channel excavation in 1972, straightened and deepened the Athabasca River at the location of a large meander bend where ice-jam floods occurred, and reduced flood frequency at PAD 23. The EB, a natural avulsion that occurred in 1982, has increased flood frequency at PAD 31 because it directs substantial and increasing Athabasca River flow towards PAD 31 via Mamawi Creek. Further details on these geomorphic changes are provided in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Wolfe6" target="_blank">[27]</a>.</p

Alignment of duplicate cores.

<p>Graphs showing stratigraphic profiles of organic matter content in duplicate cores taken from each of the three study lakes in the Peace-Athabasca Delta, northern Alberta. One of the cores from each lake was analyzed for ²¹⁰Pb dating and the other provided material for analysis of PACs. Upper panel <b>a)</b> shows the raw data, whereas the lower panel <b>b)</b> shows the data after minor vertical adjustment of the organic matter content profile for the core that was not dated. ²¹⁰Pb-derived dates from the dated core were transferred to the corresponding undated cores used for PAC analyses. No depth adjustments were required for cores from PAD 18.</p

Time trends of river-transported bitumen-associated indicator PACs.

<p>Stratigraphic records from sediment cores of the three study lakes (PAD 31, 23, 18) showing <b>a)</b> the sum of the concentrations of the seven river-transported bitumen-associated indicator PACs (C2-through C4-dibenzothiophenes, C2- through C4-fluoranthenes/pyrenes, C2-sub’d B(a)A/chrysene), and <b>b)</b> the sum of the proportions of the seven river-transported bitumen-associated indicator PACs. Grey shading identifies periods when the lakes were flood-prone. Absence of shading identifies periods when the lakes were not flood-prone. The dotted vertical line in plots for PAD 18 identifies 1967, the year when major commercial operations began <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Schindler1" target="_blank">[1]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Gosselin1" target="_blank">[4]</a>. Dashed horizontal lines in panels <b>a)</b> and <b>b)</b> correspond to the average value for the sum of the seven river-transported bitumen-associated indicator PACs in the 2007 Athabasca Delta flood deposit, where <b>a)</b> shows the concentration ( = 0.638 mg/kg) and <b>b)</b> shows the proportion ( = 0.254).</p

Relations between polycyclic aromatic compound concentration and organic matter content in river versus lake sediment.

<p>Scatterplot showing the relations between organic matter (as a percentage of dry sediment mass) and concentration of river-transported bitumen-associated indicator PACs in sediments of lakes PAD 23 (red circles) and PAD 31 (yellow circles) in the Athabasca Delta (data from this study), in bottom sediments of the Athabasca River and its distributaries at four stations within the Athabasca Delta (open symbols; data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Regional1" target="_blank">[56]</a>), and in sediments deposited on land between Mamawi Creek and PAD 31 by an ice-jam flood in spring of 2007 (blue circles; data from this study). Data include the sum of the concentration of six of the seven river-transported bitumen-associated indicator PACs that were common to both the lake sediment data set (this study) and the river bottom sediment from RAMP <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Regional1" target="_blank">[56]</a> (note: FLPY-4 was not reported by <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Regional1" target="_blank">[56]</a>). The lines of best fit (solid black line) and 95% prediction intervals (dashed red lines) are presented for linear regressions of sediment organic matter content and river-transported bitumen-associated indicator PAC concentrations for both the river bottom sediments and the lake sediments.</p

Composition of polycyclic aromatic compounds in oil sands and river sediment downstream of McMurray Formation.

<p>Bar graphs showing average composition of polycyclic aromatic compounds (PACs), expressed as relative concentration (proportion; error bars = ±1 SEM) in <b>a)</b> oil sands samples from Syncrude, Steepbank River mouth, and east and west banks of the Athabasca River (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Kelly1" target="_blank">[10]</a>), <b>b)</b> natural oil sands region river sediment (from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Colavecchia2" target="_blank">[44]</a>) and <b>c)</b> the 2007 Athabasca Delta flood deposit. Names of the PAC compounds and the corresponding codes are presented along the lower expanded horizontal axis. Blue vertical bars are PACs identified by SIMPER analysis as river-transported bitumen-associated indicator PACs deposited during flood-prone intervals (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone-0046089-t001" target="_blank">Table 1</a>). Red vertical bars are PACs identified as common in sediments deposited during not flood-prone periods. <b>*</b> identifies PACs that were not measured in one sample but were measured and reported in another sample presented in the figure.</p

Time trends of total PAC concentration.

<p>Stratigraphic records showing the total PAC concentration (solid line) and the concentration of the seven PACs indicative of a bitumen origin and transport by the Athabasca River (dotted line) in the sediment cores from lakes PAD 31, PAD 23 and PAD 18. Grey shading identifies periods when the lakes were flood-prone. Absence of shading identifies periods when the lakes were not flood-prone. The vertical dashed-dotted line in the plot for PAD 18 identifies 1967, the year when major commercial oil sands operations began <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Schindler1" target="_blank">[1]</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0046089#pone.0046089-Gosselin1" target="_blank">[4]</a>. The dashed horizontal line in all three panels corresponds to the average value for the total PAC concentration in the 2007 Athabasca Delta flood deposits (2.518 mg/kg).</p

Indicator PACs for flood-prone and not flood-prone sediments.

<p>Results of similarity percentages (SIMPER) analysis of PAC composition in sediment core samples from the three study lakes of the Peace-Athabasca Delta, northern Alberta, with samples categorized as flood-prone or not-flood prone, to identify PACs most indicative of river transport versus other vectors and processes.</p