Chronology of Atmospheric Deposition of Arsenic Inferred from Reconstructed Sedimentary Records
Bibliographic record
Abstract
Vertical distributions of As, Fe, and organic C were determined in dated (210Pb and 137Cs) sediment cores obtained from two adjacent basins (one perennially oxic and the other seasonally anoxic) of an oligotrophic headwater lake where atmospheric deposition is the only input of anthropogenic As. Despite similar sources in the two basins, the As profiles in the sediments differed markedly. Differences include the following: (i) As concentrations increased sharply upward close to the sediment surface in the perennially oxic basin due to scavenging of upward diffusing As by Fe oxyhydroxides, whereas they decreased in the seasonally anoxic basin where As scavenging by Fe oxyhydroxides did not occur, and (ii) the magnitude and position of major subsurface As maxima differed between the two basins. We applied a one-dimensional transport-reaction equation to porewater As concentration profiles obtained at the two sites to estimate sedimentary As concentrations at the time of deposition as well as subsequent addition or removal of As at various sediment depths. By multiplying As concentrations at the time of deposition by sediment mass accumulation rates, we were able to estimate variations in As fluxes at the sediment surface over the last two centuries. These fluxes were then transformed into atmospheric As deposition fluxes by applying a correction for basin-specific processes using the ratio of expected from atmospheric deposition to measured unsupported 210Pb inventories at the sampling sites. The resulting chronological profiles of atmospheric fluxes of As deposition are similar in both basins, and are consistent with both the history of specific markers for coal combustion and direct historical measurements of As in dry and wet atmospheric deposition in rural areas of North America. We conclude that the history of As inputs can be reconstructed from As sedimentary records using appropriate corrections for diagenesis and basin-specific processes.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.001 |
| Science and technology studies | 0.000 | 0.005 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.004 | 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 teacher head, 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".