Mercury Methylation and Methylmercury Demethylation in Boreal Soils and Sediment – Anthropogenic Impacts
Bibliographic record
Abstract
Methylmercury (MeHg), the most toxic form of mercury (Hg), bioaccumulates in aquatic biota, such as fish, and can ultimately cause permanent damage in the central nervous system. Forest soils store large amounts of Hg, in which MeHg constitutes relatively small fractions. Forest harvesting, a globally increasing anthropogenic activity that causes landscape disturbance, can enhance MeHg production and exports. However, harvesting impacts on MeHg production and concentrations, including measures that can alleviate and factors that can regulate these impacts, in soils and stream sediment are not fully understood. This thesis measures and compares concentrations, production and degradation of MeHg across different habitats (upland, riparian and wetland soils and stream sediment) from numerous small boreal forested watersheds before and after forest harvesting. Results revealed that stream sediment plays an important, but vastly overlooked, role in MeHg production in boreal ecosystems. Stream sediment has the strongest MeHg production among all studied habitats and is also the most sensitive habitat to forest harvesting. This thesis also provides evidence to the effectiveness of best forest management practices for preventing enhanced MeHg production and concentrations in stream sediment within harvested forests. More studies, including investigations on relationships between sediment dissolved organic matter quantity and composition and MeHg production, reveal that inputs of bioavailable Hg(II), over organic matter, play an important role controlling net MeHg production in stream sediment in harvested watersheds. Long-term effects of historical sulphate pollution, a common environmental perturbation caused by human activity, on MeHg production in lake sediment were also examined. Compared to wetland systems, high MeHg production and concentrations in lake sediment due to legacy sulphate pollution can persist for at least decades after sulphate inputs are managed. Overall, this thesis characterizes Hg distributions among boreal soils and sediment, identifies the underappreciated, important role of stream sediment in MeHg production, and advances our understanding of the cycling processes of Hg regulating MeHg production and concentrations within anthropogenically disturbed environments.
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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 | 0.000 |
| 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".