Winter nitrification contributes to excess NO<sub>3</sub><sup>−</sup> in groundwater of an agricultural region: A dual‐isotope study
Bibliographic record
Abstract
Conventional thinking is that bacterial nitrification leading to labile nitrate in fertilized agricultural soils of northern regions greatly diminishes during winter. We have carried out seasonal water sampling over 2 years to understand the fate of nitrate present in a rapidly responding groundwater/surface water system. Nitrate results show no seasonal δ15N trend. Significant δ18O downward shifts were observed between the spring‐summer and autumn‐winter periods of 2003–2004 (10.0‰) and 2004–2005 (1.3‰). Using mass‐balance mixing calculations of soil leachate with groundwater and assuming seasonal nitrification, we reproduce the observed water and nitrate oxygen‐isotope trends. These calculations suggest that nitrification takes place throughout all seasons. We also use a hydroclimatic index to establish a relationship between δ18O values in nitrate and recharge weighted by temperature. Our findings imply that nitrifying activities occur all year long and that winter nitrate production is high. This conclusion has important implications for modeling the nitrogen cycle of regions where seasonal changes in soil water mark the oxygen isotopes of nitrate.
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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 | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 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".