Effects of urban pollution on stream ecosystem functioning
Bibliographic record
Abstract
During the last century pollution generated in urban areas has become a prevalent impact in most streams and rivers worldwide.Although many waste water treatment plants (WWTP) have been implemented to reduce pollution, they do not eliminate it completely and their effluents still contribute complex mixtures of pollutants.The ecological effects of these effluents depend on their chemical composition and the final concentration in the receiving water body, which varies with the water flow of the receiving river or stream.While the effects of urban effluents on stream water quality are relatively well studied, we still lack a clear picture about their effects on ecosystem processes.This dissertation analysed the effects of urban pollution on stream ecosystem functioning, by combining observational and manipulative experiments.The effects of pollution can be exacerbated when stressors operate in concert.Among these, hydrological alterations are of special concern, either natural or human-induced, as low flows reduce the dilution capacity of the streams.Thus, I first assessed the joint effects of urban pollution and water stress on stream functioning.I studied several ecosystem processes in 13 Mediterranean streams of contrasting dilution capacity, and defined in each stream a control site and an impact site, upstream and downstream from the sewage inputs, respectively.Urban effluents caused complex effects on ecosystem functioning, but most ecosystem rates increased in proportion to pollutant subsidies of labile organic matter, nutrients and pharmaceutically active compounds.The main driver of the variability observed in ecosystem functioning, were variations in water chemistry, especially in the concentration of pharmaceutical drugs.These results show the effects of pollution to depend on the effluent nature and its dilution in the receiving stream, and that even highly concentrated urban effluents tend to subsidize biological activity.The effects of WWTP effluents are difficult to measure in the field by comparing reaches upstream and downstream from the effluent input, as the upstream sites are usually affected by other sources of pollution.This situation calls for a manipulative experiment, which I performed following a Before-After/Control-Impact design.Part of the effluent of a large tertiary urban WWTP was diverted into a small nearly unpolluted stream and the effects were assessed during a whole year.Despite of being highly diluted, the effluent subsidized most of the measured processes, only a few remained unaffected, and biofilm nutrient uptake capacity was the only being reduced.These results show that even highly diluted effluents can exert significant effects on stream ecosystem functioning.Theoretically, we expected WWTP effluents to cause a subsidy-stress response on ecosystem functioning depending on their final dilution, but the two studies so far discussed showed no such a pattern.Therefore, we performed a laboratory experiment in which a series of artificial streams were subjected to a gradient of WWTP effluent concentration, ranging from pure stream water to pure effluent.Biofilm biomass accrual was the only process following the subsidy-stress pattern, whereas WWTP effluent subsidized most processes, although they showed complex responses to their
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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 | 0.000 | 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 | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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".