A regional assessment of occurrences, sources and fate of nitrate in groundwater of Alberta
Bibliographic record
Abstract
Nitrate contamination in groundwater is a widespread problem in Europe, Northern America, Asia, and elsewhere due to adverse health effects if the water is used for drinking purposes. The objectives of this study were to a) assess the occurrence of nitrate in groundwater throughout the province of Alberta (Canada), b) to use isotope techniques to assess the predominant sources of nitrate in groundwater, and c) to use a combination of chemical and multi-isotopic techniques to assess the fate of groundwater nitrate. The study utilized >60,000 NO3-N concentration data points from domestic water wells supplemented by 986 chemical and isotopic data points collected from groundwater monitoring water wells in Alberta. In Alberta, nitrate has been detected in 34% (22,943 out of 66,421 samples) of the groundwater samples collected from domestic wells and NO3-N concentrations range from <0.005 to 421 mg NO3-N/L. Nitrate was detected in 18% (180 out of 986 samples) of the groundwater samples collected from monitoring wells with nitrate concentrations ranging from <0.004 to 300 mg NO3-N/L. Nitrate levels in 3.4% (2279 of 66,421 samples) of groundwater samples from domestic wells and <1% (8 out of 986 samples) of groundwater samples from monitoring wells were above the maximum allowable concentration (MAC) in drinking water of 10 mg/L NO3-N. To determine the sources of nitrate in groundwater, we used a multi-isotope approach on a subset of groundwater samples (n < 70) from monitoring wells. Three different potential sources of nitrate in groundwater were identified: 1) nitrate from microbial nitrification of soil organic matter and/or synthetic fertilizers represented by samples with δ15N <+6‰ and δ18O <+5‰; 2) manure-derived nitrate characterized by δ18O values <+5‰ and elevated δ15N values of >+10‰ combined with elevated nitrate concentrations; and 3) in a few cases geogenic nitrate in weathered glacial tills where clay-derived ammonium was oxidized to nitrate resulting in the highest nitrate concentrations and unique isotopic compositions of nitrate with δ15NNO3values near 26 ‰ and δ18ONO3 values of +5 ‰. We also found that the occurrence and concentration of groundwater nitrate was critically dependent on the redox conditions in the aquifers. Geochemical analyses revealed that 66% of all groundwater samples were moderately to highly reducing suggesting that denitrification is a widespread NO3 removal process in groundwater in Alberta. Compiling geochemical and multi-isotopic data enabled us to assess the occurrence and the origins of nitrate in groundwater in Alberta and identify denitrification as an important natural attenuation process that has the potential to remove nitrate from the investigated aquifers.
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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 | 0.002 |
| Science and technology studies | 0.001 | 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".