Understanding Sources and Cycling of Mercury in Terrestrial and Aquatic Ecosystems Using Mercury Stable Isotopes
Bibliographic record
Abstract
Mercury (Hg) is a trace metal pollutant that is a neurotoxin, found in both inorganic (IHg: Hg0, Hg2+) and the more toxic organo-metallic (e.g., monomethylmercury, MMHg) forms. Both historically and currently, IHg was/is released into aquatic ecosystems through industrial and mining activities, where it can be transformed into MMHg, that bioaccumulates in food webs and poses risks to both humans and wildlife. Legacy Hg pollution can still pose a threat to modern ecosystems if it becomes methylated. Hence, it is crucial to locate legacy IHg sources, understand the processes and environments that convert IHg to MMHg, and determine whether this MMHg is still entering food webs. In chapter 2, Hg isotopic compositions are used to link Hg discharges from a former chlor-alkali plant to Hg in contaminated sediments and lower trophic biota in the St. Clair River. This project is a good example of a setting where Hg isotopes successfully delineated Hg sources and demonstrated that a legacy Hg source (decades old) is still entering the food web. Chapter 3 presents a more complex system where multiple Hg sources converge and mix. Because the isotopic compositions of Hg-contaminated sediments from the historically industrialized St. Lawrence River fell within the range of documented industrial Hg isotopic signatures, they were not able to distinguish between various industrial sources, such as chlor-alkali and paper and pulp industries, due to the mixing and similarity of the isotopic compositions of the sources. However, Hg isotopes support how pervasive industrial Hg contamination is in the region. Chapter 5 delves into the atmosphere-terrestrial cycling of Hg, particularly the isotopic fractionation as plants uptake and adsorb Hg from the atmosphere. Because Hg isotopes are now an important tool to delineate and quantify sources and deposition pathways to forest soils, which are one of the largest sinks of Hg, I investigated the consistency of the atmosphere-vegetation Hg isotopic offsets between and within different plant species, as this is a crucial variable in isotopic modelling. In a Canadian boreal-deciduous mixed forest (Limberlost Forest and Wildlife Reserve), offsets were reasonably consistent between and within species. This dissertation demonstrates the utility of Hg isotopes in source characterization and quantification, but also highlights some of the limitations of using Hg isotopes.
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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 | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| 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".