The role of smelter emissions and element remobilization in the sediment chemistry of 99 lakes around the Horne smelter, Quebec
Bibliographic record
Abstract
Ninety-nine lakes were sampled at varying distances up to 75 km from the Horne smelter at Rouyn-Noranda, Quebec, to study the influence of the smelter versus other factors on metal concentrations in lake sediments. Most of these lakes lie within the Abitibi Greenstone Belt, a zone of extensive base metal and gold mineralization and the focus of a mining and smelting economy for almost a century. Lake sediment cores, c . 25 cm long, were collected and sampled at the top (0–2 cm) and the bottom (18–20 cm) to capture sediment that was deposited after the smelter was in operation (‘post-industrial’) and well before the mining and smelting activity was started (‘pre-industrial’). Additionally, nine cores were sampled in 1 cm increments to depths of up to 50 cm to study temporal patterns and potential element remobilization in detail. The cores were analysed for an extensive suite of elements. This paper focuses on those elements that are emitted by the smelter for which there are records of emissions through time, namely As, Cd, Cu, Pb and Zn. A spatial statistical approach – a logistic model of metal content versus distance from the smelter – was used investigate the relationship of sediment chemistry with smelter emissions and other possible influences. Using Cu as a representative proxy for the other emitted metals, this analysis demonstrates that elements are enriched in lake sediments by a factor of about three times around the smelter, that the impact of the smelter is detectable in lakes to a distance of at least 50 km, and that there is no obvious association between sediment Cu concentration and bedrock geology, land-use, lake pH, or lake morphometry (lake area/lake catchment area). The nine lakes studied in detail show enrichment towards the sediment–water interface (SWI) and relatively steady concentrations below depths of c . 10 cm. However, depth profiles do not match changes in the magnitude of smelter emissions through time, nor do they match changes in emission chemistry (element ratios) through time. Element ratios do generally move towards the chemistry of the emissions, suggesting smelter influence, but do not do so predictably. For example, (i) trends in the Cu/Pb ratio continue to the very bottom of cores into material deposited hundreds of years before industrialization, and (ii) proximity to the smelter does not lead to greater similarity between sediment and emission chemistry. These results suggest that significant element remobilization is occurring and that it differs from lake to lake and from element to element. We conclude that lakes within 50 km of the smelter have elevated metal concentrations in their near-surface sediments due to stack emissions but, due to element cycling and mobility, it is difficult to quantitatively determine the magnitude of metal increase attributable to the smelter. We also suggest that due to upward remobilization, the duration of industrial metal enrichments in surface sediments (the residence time) may be increased, thereby making surface enrichments more persistent than would be predicted by the sedimentation rate.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".