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

Fulvio Franchi* (Corresponding Author), Jason M.E Ahad, Josie Geris, Gaone Jhowa, Alfred K Petros, Jean-Christophe Comte

*Corresponding author for this work

Research output: Contribution to journalArticle

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.
Original languageEnglish
Number of pages19
JournalJournal of Soils and Sediments
Early online date18 Nov 2019
DOIs
Publication statusE-pub ahead of print - 18 Nov 2019

Fingerprint

arid environment
mobilization
drought
pollutant
sediment
rainfall
metal
heavy metal
cyclone
extreme event
trace metal
sediment core
vertical distribution
grain size
hazard
aquifer

Keywords

  • Botswana
  • Dineo cyclone
  • Flood
  • Limpopo catchment
  • Sediments contamination

Cite this

@article{8e23e1dc01be444d8f517749d9bde85f,
title = "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",
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.",
keywords = "Botswana, Dineo cyclone, Flood, Limpopo catchment, Sediments contamination",
author = "Fulvio Franchi and Ahad, {Jason M.E} and Josie Geris and Gaone Jhowa and Petros, {Alfred K} and Jean-Christophe Comte",
note = "Open access via the Springer Compact Agreement This research was funded by the UK Natural Environment Research Council NERC Urgency grant NE/R002568/1 (PULA Project). Acknowledgments The authors would like to thank the Editor and two anonymous reviewers for their comments and suggestions which have contributed to improve the quality of this paper. The authors would like to thank all the BIUST students that took part in one or more field campaigns in the Notwane river catchment; their work and interests were remarkable. Thanks are due to Trust Manyiwa (BIUST) for the assistance with grain size and OM analyses and to Serwalo M. Mokgosi (BIUST) for assistance with the MP-AES measurements of sediment materials. We would like to thank the staff at the University of Aberdeen laboratory (Michael McGibbon) for assistance with the water quality analyses.",
year = "2019",
month = "11",
day = "18",
doi = "10.1007/s11368-019-02454-9",
language = "English",
journal = "Journal of Soils and Sediments",
issn = "1614-7480",
publisher = "Springer",

}

TY - JOUR

T1 - Modern sediment records of hydroclimatic extremes and associated potential contaminant mobilization in semi-arid environments

T2 - lessons learnt from recent flood-drought cycles in southern Botswana

AU - Franchi, Fulvio

AU - Ahad, Jason M.E

AU - Geris, Josie

AU - Jhowa, Gaone

AU - Petros, Alfred K

AU - Comte, Jean-Christophe

N1 - Open access via the Springer Compact Agreement This research was funded by the UK Natural Environment Research Council NERC Urgency grant NE/R002568/1 (PULA Project). Acknowledgments The authors would like to thank the Editor and two anonymous reviewers for their comments and suggestions which have contributed to improve the quality of this paper. The authors would like to thank all the BIUST students that took part in one or more field campaigns in the Notwane river catchment; their work and interests were remarkable. Thanks are due to Trust Manyiwa (BIUST) for the assistance with grain size and OM analyses and to Serwalo M. Mokgosi (BIUST) for assistance with the MP-AES measurements of sediment materials. We would like to thank the staff at the University of Aberdeen laboratory (Michael McGibbon) for assistance with the water quality analyses.

PY - 2019/11/18

Y1 - 2019/11/18

N2 - 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.

AB - 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.

KW - Botswana

KW - Dineo cyclone

KW - Flood

KW - Limpopo catchment

KW - Sediments contamination

U2 - 10.1007/s11368-019-02454-9

DO - 10.1007/s11368-019-02454-9

M3 - Article

JO - Journal of Soils and Sediments

JF - Journal of Soils and Sediments

SN - 1614-7480

ER -