Indigenous Sediment Microbial Activity in Response to Nutrient Enrichment and Plant Growth Following a Controlled Oil Spill on a Freshwater Wetland
Bibliographic record
Abstract
The population density and activity of a microbial community associated with the sediment and rhizosphere of an intertidal freshwater wetland dominated by Scirpus pungens was monitored before and following the application of weathered Mesa light crude oil and fertilizers. The influence of nutrient enrichment (fertilizers) and plant growth on oil degradation rates was determined from the resulting data. The study plots (four blocks of replicates) were subjected to five treatments: oil only (natural attenuation); oil plus ammonium nitrate and phosphate, with regular cropping of the plants; oil plus ammonium nitrate and phosphate; oil plus sodium nitrate and phosphate; no oil, ammonium nitrate and phosphate. The plots were regularly monitored in the field for gas production (carbon dioxide and nitrous oxide), and samples were collected for laboratory analysis of denitrification activity, aliphatic and aromatic hydrocarbon degradation activity, and total heteroptrophic bacteria. The viable bacterial population density increased during the first 4 weeks in oiled and unoiled experimental plots that were fertilized. In contrast, population densities in untreated areas remained relatively unchanged throughout the monitoring period. The microbial population demonstrated a rapid and sustained increase in naphthalene mineralization activity in plots that were both fertilized and oiled. Hexadecane mineralization activity increased in response to fertilizer application, with ammonium nitrate causing a larger increase than sodium nitrate. A very significant difference observed in the mineralization of hexadecane was that the surface sediments were much more active than the subsurface sediments. This difference became even more pronounced in the second year of monitoring, even though the treatment regime had been discontinued. This compartmentalization of mineralization activity was not observed for naphthalene. Following fertilizer application, field and laboratory evaluation of nitrogen metabolism in the sediments indicated significant denitrification activity that was not adversely affected by oiling. The results demonstrated that the application of fertilizers stimulated the activities of indigenous hydrocarbon-degrading and denitrifying bacteria, and the presence of oil either enhanced or had no detrimental effect on these activities. As a remediation strategy, the application of fertilizers to a wetland shoreline following an oil spill would promote the growth of indigenous plants and their associated microbial flora, resulting in increased metabolic activity and the potential for increased oil degradation activity.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.002 | 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 teacher head, 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".