The Optical, Chemical, and Molecular Dissolved Organic Matter Succession Along a Boreal Soil‐Stream‐River Continuum
Bibliographic record
Abstract
Abstract Soils export large amounts of organic matter to rivers, and there are still major uncertainties concerning the composition and reactivity of this material and its fate within the fluvial network. Here we reconstructed the pattern of movement and processing of dissolved organic matter (DOM) along a soil‐stream‐river continuum under summer baseflow conditions in a boreal region of Québec (Canada), using a combination of fluorescence spectra, size exclusion chromatography and ultrahigh resolution mass spectrometry. Our results show that there is a clear sequence of selective DOM degradation along the soil‐stream‐river continuum, which results in pronounced compositional shifts downstream. The soil‐stream interface was a hot spot of DOM degradation, where biopolymers and low molecular weight (LMW) compounds were selectively removed. In contrast, processing in the stream channel was dominated by the degradation of humic‐like aromatic DOM, likely driven by photolysis, with little further degradation of either biopolymers or LMW compounds. Overall, there was a high degree of coherence between the patterns observed in DOM chemical composition, optical properties, and molecular profiles, and none of these approaches pointed to measurable production of new DOM components, suggesting that the DOM pools removed during transit were likely mineralized to CO2. Our first order estimates suggest that rates of soil‐derived DOM mineralization could potentially sustain over half of the measured CO2 emissions from this stream network, with mineralization of biopolymers and humic substances contributing roughly equally to these fluvial emissions.
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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 | 0.001 | 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".