Evidence for the diagenetic formation of fused aromatic ring structures in an organic soil
Bibliographic record
Abstract
Understanding the molecular make-up of recalcitrant organic matter (rSOM) is important to postulate the capability of soil organic matter (SOM) to sequester carbon and mitigate climate change. Humic acid (HA) extracted from the river bed sediment (RS) from the West Holland river was analyzed, aiming to characterize and quantify the fused ring aromatic structures (FRA) portion. FARs can be formed through condensation and polymerization reactions and act as an important skeletal structure of the rSOM which has a mean residence time >1000 years. We conducted a series of nuclear magnetic resonance (NMR) experiments, 13C Direct Polarization Magic Angle Spinning (DP-MAS) NMR spectroscopy, and Dipolar dephased (dd) DPMAS NMR, chemical shift anisotropy (CSA) cross-polarization (CP) total sideband suppression (TOSS) NMR experiment and a dd-CSA filtered CPTOSS to accurately quantify the proportion of FRAs in the sediment HA sample. We compared the proportions of the functional groups of the RS with the surface (0-20 cm, TS) and deep (>90 cm, CS) soil HAs of the nearby Holland Marsh, Muck Crops Research Station to understand the linkages and the transformations of SOM happened while transportation (wind erosion and horizontal seepage) to the muck river sediment. We found that 90% of the aromatic C in the RS is non-protonated, and 32% of the aliphatic region was non-protonated. The DPMAS spectral comparison between RS, TS and CS clearly showed that RS contains characteristic peaks of both TS and CS. Moreover, the proportion of non-protonated aliphatics in RS (32%) is high compared to TS (18%) and CS (29%). Our results indicate that in muck river sediment soil HA, non-protonated aliphatics (CRAM-like structures) contribute to the rSOM more than FRAs, while in TS and CS, FRAs' contribution is higher than the non-protonated aliphatics. Collectively our results show the link between terrestrial organic matter transportation to the river sediment and the transformation that occur in the rSOM fraction in the river sediment SOM. This new knowledge allows us to understand the structural changes that happen in the sequestered carbon in different soil 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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".