Ten thousand years of bitumen transport in the lower Athabasca River, Canada
Bibliographic record
Abstract
The lower Athabasca River valley in northeastern Alberta, famous for oil sands mining, was also the site of one of North America largest Ice Age floods. During deglaciation, a large proglacial lake, Lake Agassiz, drained catastrophically through the Athabasca River valley. This catastrophic flood eroded deeply into the bitumen-bearing Clearwater and McMurray Formations, transporting and then depositing bitumen in what is now the Peace-Athabasca Delta. Modern erosion of these flood deposits represents an important source of polycyclic aromatic hydrocarbons (PAHs) to the Athabasca River. This erosion occurs primarily at the Big Bend site, a large, 18 m high and 4,200 m wide cut bank, actively eroded by the Athabasca River. In this thesis, I estimated the contribution of the Big Bend exposure to the sediment and PAH budgets of the lower Athabasca River. The Big Bend is estimated to supply ~410 kt of sediment annually to the lower Athabasca River, which represents ~35 % of the sediment budget between Fort McMurray and the Peace-Athabasca Delta. The erosion of secondary bitumen deposits within the Big Bend exposure is estimated to contribute ~5.3 tons of PAHs to the river each year. PAHs from the Big Bend site are characterized by a unique compositional profile that can be distinguished from other PAH sources. Specifically, the secondary bitumen emplaced within the Big Bend section contains a higher alkylated PA4/PA3 ratio than other PAH sources in the lower Athabasca River region. These other sources of PAHs include primary bitumen from the McMurray Formation, as well as wildfire ash and petroleum coke, which is a by-product of bitumen upgrading. To understand the relative contribution of the various sources of PAHs to the Athabasca River, I compared these results with results from an ambient water quality monitoring program. Water samples were more similar to raw bitumen and Big Bend during months of high-flow, but matched better with forest fire ash and fluid petroleum coke during low-flow periods. These results suggest the natural bank erosion of the Athabasca River during periods of high discharge plays an important role in supplying PAHs to the lower Athabasca River and the downstream Peace-Athabasca Delta. This study has revealed that the erosion of reworked bitumen at Big Bend is a major source of PAH input to the lower Athabasca River region. This (natural) source of PAHs occurs in addition to inputs resulting from the extraction and processing of bitumen. These industrial inputs have led to increasing burdens of PAHs – and especially alkylated PAHs – across the region. Understanding the fate, biological uptake, and indeed prevalence of the various PAH sources within ecosystems and biota therefore requires additional research.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.003 |
| Science and technology studies | 0.002 | 0.000 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.003 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".