Cumulative disturbance effects on phosphorus mobility in a gravel-bed river at the catchment scale
Bibliographic record
Abstract
Landscape disturbance pressures in forested headwater regions can modify both the supply and transport of sediment from hillslopes to river networks. The effects of these pressures on phosphorus (P) mobility in rivers vary regionally depending upon the type and severity of the disturbance as well as interactions amongst other watershed scale controls such as climate, geology, hydrology and vegetation. The present study examines P dynamics in a gravel-bed river across multiple disturbances during environmentally sensitive periods of summer low-flow. Six study sites were selected to represent a gradient of sediment pressures from landscape disturbances (e.g., roads, harvesting, wildfire, sewage) in the Crowsnest River, Alberta. Interactions between fine bed sediments and soluble reactive phosphorus (SRP) were examined using equilibrium phosphorus concentrations (EPC0) and diffusive fluxes of SRP from the riverbed sediments. Diffusive fluxes at each site were estimated using gradients of SRP between pore-water in the bed and water column, determined from vertical distributions of SRP in the gravel matrix measured with pore-water peepers. SRP concentrations in pore-water were variable among depths and sites but were elevated downstream of the stream reach receiving primary sewage effluent outflow. Larger SRP concentration gradients were observed at sites that had either smaller substrate or increased biofilm activity. The EPC0 and diffusive pore-water flux data suggest that fine sediment in the riverbed acted as a source of SRP to the water column under low-flow conditions when the risk for eutrophication is higher and such conditions favor the growth of biofilms. EPC0 concentrations showed large inter- and intra-site variability indicating heterogeneous responses to disturbance. Furthermore, overlapping, and varying proportions of historic and contemporary harvesting, roads, road-stream or culvert crossings, and OHV use confounds the apportionment of landscape impacts. This study provides insight into the potential for the regulation of P by sediments in gravel-bed rivers following a range of landscape disturbance effects.
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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 | 0.000 | 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) | 0.001 | 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".