Using 222Rn to quantify wetlands interflow volume and quality discharging to headwater streams
Bibliographic record
Abstract
Headwater streams are highly dependent on groundwater discharge to maintain low flows during dry periods and to dilute pollutants. Groundwater discharge to streams can have different flow paths, either from groundwater flowing directly to the river through the hyporheic zone or groundwater that emerges at the contact with a riparian wetland and flows mainly on the wetland surface. Differentiating these flows could be useful to assess the contribution of riparian wetlands in protecting stream water quality. The objective of this research was to expand the use of 222Rn as a groundwater tracer for small streams in headwater catchments to distinguish flows received directly from the aquifer and through riparian wetlands. 222Rn activities, phosphate (PO43-) and nitrate (NO3-) concentrations, along with stream flows were used in a mass balance model to establish the proportions of groundwater flow that discharge to a small stream located southwest of the Paris Basin (France). This watershed is typical of headwater catchments in this region because it receives a wastewater treatment plant (WWTP) effluent at its source and its banks are occupied by many small riparian wetlands. To obtain the best accuracy of groundwater flow assessment, the field work was done during low flow conditions, where the stream flow was only 0.079 m3/s at the outlet. The model gives a good estimation of each flow path with 83 % of the stream baseflow originating from riparian wetlands. The large contrast in 222Rn activity between groundwater inflow from the aquifer (mean of 21200 Bq/m3) and interflows from wetlands (mean of 2310 Bq/m3) renders the mass balance model sensitive to the separation of these two types of groundwater flow paths. At the head of the stream, water is characterized by high concentrations of PO43- and NO3- due to the WWTP effluent into the stream (13 and 21 mg/L respectively). All groundwater flows are PO43- free and contribute to the improvement of stream water quality. The NO3- cycle is more difficult to constrain because of the spatial heterogeneity in groundwater concentrations. Nevertheless, the results of the modeling approach showed that the main part of the evolution of NO3- concentrations along the river can be explained by the dilution of stream flow with interflows. The method developed is considered sufficiently accurate to quantify groundwater inflows for different flow paths in headwater catchments and to estimate the impact of groundwater flow paths on stream water quality.
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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 | 0.000 |
| 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) | 0.000 | 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 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".