Modern sediment records of hydroclimatic extremes and associated potential contaminant mobilization in semi-arid environments: lessons learnt from recent flood-drought cycles in southern Botswana
Why this work is in the frame
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Bibliographic record
Abstract
Abstract Purpose The aim of this work was to identify and analyze the records of flood-drought cycles as preserved in the sediments of the Notwane reservoir, southern Botswana, in order to better understand how extreme events affect water and sediment quality. This work represents the first attempt to study the reservoir sediments in arid to semi-arid environments and suggests that they could be used as proxies for the characterization of the effects of flood-drought cycles. Materials and methods For the first time in an arid context like Botswana, sediments from artificial reservoirs were explored through correlating sediment records with the presence and quantity of pollutants in the reservoir’s wider arid and semi-arid catchment after the latest extreme flood event of 2017. Sediments from the Notwane reservoir were collected with a push corer to a maximum depth of 80 cm. Sediments were then analyzed for grain size distribution, organic matter content, and concentrations of heavy metals (Fe, Zn, Cu, Cr, and Pb). Concentrations of heavy metals from surface water and groundwater were compared with the metal profiles from the sediment cores and with rainfall series from the CHIRPS (Climate Hazards Group InfraRed Precipitation with Stations) database. Results and discussion The sediments from Notwane reservoir clearly showed two flood couplets characterized by fining upward beds. Water quality data from Notwane reservoir and the surrounding aquifer showed peaks of contaminants following rainfall. Although the couplets found in the sediment record were not always clearly coupled with peaks of metals, some correlation was found between the vertical distribution of metals within the sediments and the most recent sequence and the seasonal metal variation in water. Overall, trace metal contents were very low: < 1 mg L −1 for Cu and Zn and < 2 mg L −1 for Cr and Pb, well below the sediment quality assessment guidelines (SQGs), indicating that the above-average precipitations of the last 10 years did not noticeably contribute to the input of heavy metal contaminants in the reservoir sediments. Conclusions The 2016/17 Dineo cyclone flood was triggered by above-average rainfall, preceded by a 4-year period of severe drought. The deterioration of the basin during the drought has enhanced the effects of the flood, worsening the damages on structures and livelihoods. The lessons learnt from the Dineo cyclone in Botswana highlight the importance of integrated studies that combine hydrological data, rainfall series, and sediments. It is recommended to extend the research for longer time periods.
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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 | 0.000 | 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 it