Shifts in organic matter character and microbial community dynamics from glacier headwaters to downstream rivers in the Canadian Rocky Mountains
Bibliographic record
Abstract
Climate change is causing mountain glacial systems to warm rapidly, leading to increased water fluxes from these catchments and concomitant export of glacially-derived sediment and organic matter (OM). Glacial OM represents an aged, but potentially bioavailable carbon pool that is compositionally distinct from OM found in non-glacially sourced waters. Despite this, the composition of riverine OM from glacial headwaters to downstream reaches and its role in structuring microbial communities has yet to be characterized in the Canadian Rockies. Over three summers (2019-2021) samples were collected from four glacially-fed rivers within Banff and Jasper National Parks. Samples were collected before, during and after glacial icemelt along a transect ranging 0 – 100 km downstream of glacial termini. Organic carbon (OC) isotopes (Δ14C-OC, δ13C-OC) were used to assess OM age and source, dissolved OM absorbance and fluorescence were used to assess OM character. Microbial community composition was assessed utilizing 16S rRNA gene sequencing. From headwater to rivers OM transitioned from being aged and protein-like with an apparent microbial source to being relatively younger, humic-like and sourced from plants and benthic algae. This transition was likely driven by changing catchment characteristics with movement downstream, and the presence of more developed soils. Total nitrogen, deuterium excess (correlated with glacial ice contribution), water temperature and protein-like DOM were significant in explaining microbial community structure, although only to a small extent (14%). This finding paired with the identification of a core community that made up large fraction of relative abundance at each site, indicating mass effects as driving a fraction of microbial community composition within these streams. Research into key taxa at sites near glaciers identified taxa that likely harbour adaptations to cold temperatures, nutrient poor conditions and chemolithoautotrophic metabolisms. This could indicate that glacially exported microbes can seed proglacial stream communities. Together these findings suggest that both OC cycling and microbial community structure in glacier-fed streams in the Rockies will be impacted by glacial retreat, with unknown ecosystem impacts.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.002 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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".