Chemical and isotopic evidence of fragmented recharge areas for the carbonate aquifers of the Niagara Escarpment
Bibliographic record
Abstract
The Early Silurian carbonate bedrock formations of the Michigan basin, southern Ontario, contain significant quantities of high-quality groundwater resources and provide the sole drinking water source to many large municipalities and private residences. This investigation represents the first attempt to characterize these carbonate groundwater resources in their entirety. Although the bedrock formations are relatively flat-lying and regionally extensive, suggesting ease of characterization, the systems are complex due to the influence of glacial sediment cover on recharge and the effect of karst on groundwater residence times. Recharge timing and controls are investigated with several isotopic and geochemical indicators of recent recharge in groundwater, within the context of the sedimentary geology and sediment thickness of the study area. Spatial trends of tritium, and SF6 in groundwater, interpreted as representing recent recharge (< 50 years), corroborate with aerobic redox chemistry in the carbonate groundwater systems underlying areas of thin or permeable sediment cover. Groundwater chemical evolution beyond recharge areas is assessed with general chemistry, the redox profile and an investigation of water-rock interaction. A comparison of strontium isotope ratios (87Sr/86Sr) in bedrock and groundwater shows that long residence times are required for the isotopic signature of the rock to imprint on the groundwater. Increasing Sr to Ca ratios along the groundwater flow path are likely resulting from incongruent dissolution of dolomite and the precipitation of calcite with evolution. Sulphur isotopic composition of sulphate (delta-34SSO4 and delta-18OSO4) in groundwater shows isotopic evidence of pyrite oxidation in recharge areas, and a Silurian sulphur isotopic signature in areas of thick and low permeability sediments, well downgradient of identified recharge areas. For this investigation, isotopic and hydrochemical tools have provided many essential lines of evidence, supporting the development of a conceptual model of recharge and groundwater evolution in this complex setting with many geological controls at play.
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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 | 0.001 |
| Science and technology studies | 0.001 | 0.001 |
| 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".