History of atmospheric trace metal deposition along the St.Lawrence Valley (Quebec) using peat bog records
Bibliographic record
Abstract
Human activities, especially since the Industrial Revolution, have left a legacy of trace metal contamination that is potentially harmful for natural ecosystems and human health (e.g. As, Cd, Pb) and affected their geochemical cycles. Atmospheric metal pollution is recorded in different environmental archives such as lake and marine sediments, snow and ice and peat bogs. Among these archives, peat bogs have proven to be effective in reconstructing the history of atmospheric metal deposition throughout Europe, but few studies have been carried out in North America or in Quebec. Being an important natural wind corridor, oriented from south-west to north-east, the St. Lawrence Valley is affected by long-range transport of contaminants. The present study focuses on the reconstruction of the history of atmospheric As, Cd, Ni, Pb and Zn deposition in surface cores (<100 cm) from three peat bogs along the St. Lawrence Valley. Core chronologies were established using 210Pb for the upper horizons and 14C dating for the deeper sections. Metal accumulation rates were computed from measured concentrations and core chronologies. Stable lead isotopes (204, 206, 207 and 208) were also analysed to distinguish natural and anthropogenic sources of Pb. Results show that the three cores recorded the onset of industrial activities around 1810-1850AD. As, Cd, Pb and, to a certain extent Ni deposition increased to reach a maxima in the 1940s and mid-1960s to early 1970s. Trace metals likely originated from coal-burning and ore smelting during the 19th and the first half of the 20th centuries. Thereafter, the dominant source of Pb became leaded gasolines additives until their phasing-out in the 1970s. Trace metal contents were greater in the two cores recovered in the southwestern part of the St. Lawrence Valley than in the one located 600 km to the northeast. This can likely be explained by their proximity to urban and industrial centers of St. Lawrence and Ottawa Valleys and U.S. Mid-West. The Pb isotope signatures suggest a long-range transport of contaminants from a common regional source (U.S. Mid-West, Great Lakes Region). A rapid decrease in metal accumulation rates since the 1970s suggest that the implementation of mitigation policies was effective in reducing atmospheric emissions of trace metal. Nevertheless, metal accumulation rates and stable Pb isotopes have not yet returned to pre-industrial values.
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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 | 0.002 |
| Science and technology studies | 0.001 | 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) | 0.001 | 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".