Interplay of S and As in Mekong Delta sediments during redox oscillations
Bibliographic record
Abstract
The cumulative effects of periodic redox cycling on the mobility of As, Fe, and S from alluvial sediment to groundwater were investigated in bioreactor experiments. Two particular sediments from the alluvial floodplain of the Mekong Delta River were investigated: Matrix A (14 m deep) had a higher pyrite concentration than matrix B (7 m deep) sediments. Gypsum was present in matrix B but absent in matrix A. In the reactors, the sediment suspensions were supplemented with As(III) and SO42−, and were subjected to three full-redox cycles entailing phases of nitrogen/CO2, compressed air sparging, and cellobiose addition. Major differences in As concentration and speciation were observed upon redox cycling. Evidences support the fact that initial sediment composition is the main factor controlling arsenic release and its speciation during the redox cycles. Indeed, a high pyrite content associated with a low SO42− content resulted in an increase in dissolved As concentrations, mainly in the form of As(III), after anoxic half-cycles; whereas a decrease in As concentrations mainly in the form of As(V), was instead observed after oxic half-cycles. In addition, oxic conditions were found to be responsible for pyrite and arsenian pyrite oxidation, increasing the As pool available for mobilization. The same processes seem to occur in sediment with the presence of gypsum, but, in this case, dissolved As were sequestered by biotic or abiotic redox reactions occurring in the Fe–S system, and by specific physico-chemical condition (e.g. pH). The contrasting results obtained for two sediments sampled from the same core show that many complexes and entangled factors are at work, and further refinement is needed to explain the spatial and temporal variability of As release to groundwater of the Mekong River Delta (Vietnam).
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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 | 0.000 | 0.000 |
| 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) | 0.000 | 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".