Evaluating radium as a time tracer for infiltrated surface water in unsteady surface -groundwater interaction areas
Bibliographic record
Abstract
In the critical zone, infiltrated surface water within porous media drives many biogeochemical processes that lead to a natural attenuation of contaminants. In the case of induced bank filtration (IBF), quantifying residence time is required to anticipate water quality issues. Due to combined hydroclimatic regimes and variable pumping sequences, groundwater flow is unsteady and classical residence time quantification approaches often fail to account for such dynamics. Radium is a geogenic element with four isotopes offering ideal half-life ranges for estimating groundwater residence time. Its potential to characterize water mixing processes or date seawater has been widely proven. These advances were supported by the development of affordable analysis devices such as delayed coincidence counters (RaDeCC). In freshwater, the radium adsorption ability on the porous matrix affects its mobility and reduces its availability in dissolved form. These direct consequences of adsorption i) restrict the representativity of water samples, ii) impact the ability to measure dissolved radium by RaDeCC and iii) drastically reduce the temporal range for using radium as a chronometer of surface water residence time in an aquifer. Without a paradigm change, radium as a temporal tracer in freshwater won’t reveal its full potential. However, the third point may be appropriate for tracing dynamics of unsteady flow such as those prevailing for infiltrated surface water in IBF site. A two-years study led in an IBF site equipped with eight wells and 10 piezometers allowed 200 samples to be analysed with a RaDeCC for 223, 224, 228 and 226 radium isotopes. Preliminary results suggest that dissolved radium is more controlled by flow than by a differential adsorption, as no clear correlation was found between dissolved radium and geochemistry (ORP, pH, EC). The spatial distribution pattern of short-lived isotopes at the site was related to the pumping regimes. Annual amplitudes of dissolved radium isotopes presented a periodicity for all the wells. These first results show a satisfactory tracer response to spatial and temporal hydrodynamic flow changes, either from natural or anthropogenic origin in critical zone.
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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 | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| 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".