Redox dynamics and metal cycling in the carbonate-buffered sediment–water interface of the ferruginous and sulfatic Lake Medard, Czech Republic
Bibliographic record
Abstract
ABSTRACT Lake Medard (LM), a post-mining lake in the Czech Republic with stratified, sulfate- and iron-rich bottom waters, serves as a natural laboratory to study sediment–water-interface (SWI) dynamics where steep aqueous redox gradients are present. This study investigates the interplay of redox conditions, microbial activity, and sedimentary processes, revealing that short-term Eh fluctuations (80–100 mV) in the bottom water significantly mobilize rare earth elements (REE) and influence the partitioning of other redox-sensitive elements such as vanadium (V) and arsenic (As) from reactive iron (Fe)- and manganese (Mn)-oxyhydroxides during early diagenesis. While carbonate phases like siderite primarily retain their REE signatures, they can incorporate REE released during these redox shifts. Spectroscopic analyses confirms the presence of FeOOH polymorphs (goethite and lepidocrocite) in organo-mineral aggregates in the upper sediments. Sequential extractions shows that under stronger reducing conditions (Eh ≈ –190 mV), As predominantly associates with carbonates, shifting to Fe(III)-oxyhydroxides at higher Eh (≈ –80 mV). Isotope analyses (δ13C) indicate that the bulk sediment carbonate is detrital, sourced from Miocene strata. Authigenic pyrite in LM sediments exhibits δ34Spy values (–35.1 to –23.0‰), reflecting microbial sulfate reduction. However, the accumulation of the byproduct sulfide, and thus pyrite stabilization, is limited by the low availability of labile organic substrates and the reoxidation of sulfide by Fe(III)-oxyhydroxides. These findings highlight the sensitivity of geochemical signals in sediments to subtle redox shifts and improve our interpretation of ancient deposits formed under dynamic water column redox conditions.
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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 | 0.005 | 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 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| 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 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".