Using stable water isotopes to identify spatial-temporal controls on groundwater recharge in two contrasting East African aquifer systems

Samson Oiro; Jean-Christophe Comte; Chris Soulsby; Kristine Walraevens

doi:10.1080/02626667.2018.1459625

Using stable water isotopes to identify spatial-temporal controls on groundwater recharge in two contrasting East African aquifer systems

Samson Oiro^* (Corresponding Author), Jean-Christophe Comte, Chris Soulsby, Kristine Walraevens

^*Corresponding author for this work

Ghent University

Research output: Contribution to journal › Article › peer-review

39 Citations (Scopus)

64 Downloads (Pure)

Abstract

Understanding the spatial-temporal variability in groundwater recharge is an essential prerequisite to sustainable management of aquifers. Spatial analysis of groundwater stable isotopes uncovered predominant controls on groundwater recharge in Nairobi Aquifer System (NAS) and South Coast aquifer (SC), two exemplar East-African aquifers relied upon by 7M people. 368 samples were analysed for stable isotopes and basic physico-chemical parameters. The NAS groundwater isotopes are controlled by precipitation orographic effects and enriched recharge from impounded lakes/wetlands. SC isotopes are correlated with water-table depth influencing evapotranspiration. Global Network of Isotopes in Precipitation-GNIP data revealed groundwater recharge during months of heavy rains in NAS, whilst SC experiences spatiotemporally diffuse recharge. Inferred ‘isoscapes’ show; in NAS, (1) direct, rapid recharge favoured by faults, well-drained soils and ample rainfall in uplands, (2) delayed recharge from impounded-lakes and wetlands in midlands, (3) focussed, event-based recharge in floodplains; in SC, diffuse recharge complicated by significant water-table evapotranspiration processes.

Original language	English
Pages (from-to)	862-877
Number of pages	16
Journal	Hydrological Sciences Journal
Volume	63
Issue number	6
Early online date	18 Apr 2018
DOIs	https://doi.org/10.1080/02626667.2018.1459625
Publication status	Published - 6 Jun 2018

Bibliographical note

We appreciate the financial support granted by the Royal Geography Society (with IBG), the Kenya Water Resources Management Authority (WRMA) and the University of Aberdeen. WRMA staff who assisted during groundwater sampling and J. Dick’s assistance in running isotope laboratory tests are greatly acknowledged. We are grateful to two anonymous reviewers for their relevant comments and suggestions which have contributed to improve the manuscript.

Keywords

Groundwater recharge
Stable isotopes
Aquifer systems
Meteoric water line
Evaporation effect

Access to Document

10.1080/02626667.2018.1459625Licence: Unspecified

Accepted Manuscript
This is an Accepted Manuscript of an article published by Taylor & Francis in Hydrological Sciences Journal on 18th April 2018, available online: http://www.tandfonline.com/10.1080/02626667.2018.1459625
Accepted author manuscript, 2.81 MBLicence: Unspecified

Building capacity for informed groundwater policy and practice in Eastern Africa
Jean-Christophe Comte (Coordinator)
Impact: Societal

Cite this

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title = "Using stable water isotopes to identify spatial-temporal controls on groundwater recharge in two contrasting East African aquifer systems",

abstract = "Understanding the spatial-temporal variability in groundwater recharge is an essential prerequisite to sustainable management of aquifers. Spatial analysis of groundwater stable isotopes uncovered predominant controls on groundwater recharge in Nairobi Aquifer System (NAS) and South Coast aquifer (SC), two exemplar East-African aquifers relied upon by 7M people. 368 samples were analysed for stable isotopes and basic physico-chemical parameters. The NAS groundwater isotopes are controlled by precipitation orographic effects and enriched recharge from impounded lakes/wetlands. SC isotopes are correlated with water-table depth influencing evapotranspiration. Global Network of Isotopes in Precipitation-GNIP data revealed groundwater recharge during months of heavy rains in NAS, whilst SC experiences spatiotemporally diffuse recharge. Inferred {\textquoteleft}isoscapes{\textquoteright} show; in NAS, (1) direct, rapid recharge favoured by faults, well-drained soils and ample rainfall in uplands, (2) delayed recharge from impounded-lakes and wetlands in midlands, (3) focussed, event-based recharge in floodplains; in SC, diffuse recharge complicated by significant water-table evapotranspiration processes. ",

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N1 - We appreciate the financial support granted by the Royal Geography Society (with IBG), the Kenya Water Resources Management Authority (WRMA) and the University of Aberdeen. WRMA staff who assisted during groundwater sampling and J. Dick’s assistance in running isotope laboratory tests are greatly acknowledged. We are grateful to two anonymous reviewers for their relevant comments and suggestions which have contributed to improve the manuscript.

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AB - Understanding the spatial-temporal variability in groundwater recharge is an essential prerequisite to sustainable management of aquifers. Spatial analysis of groundwater stable isotopes uncovered predominant controls on groundwater recharge in Nairobi Aquifer System (NAS) and South Coast aquifer (SC), two exemplar East-African aquifers relied upon by 7M people. 368 samples were analysed for stable isotopes and basic physico-chemical parameters. The NAS groundwater isotopes are controlled by precipitation orographic effects and enriched recharge from impounded lakes/wetlands. SC isotopes are correlated with water-table depth influencing evapotranspiration. Global Network of Isotopes in Precipitation-GNIP data revealed groundwater recharge during months of heavy rains in NAS, whilst SC experiences spatiotemporally diffuse recharge. Inferred ‘isoscapes’ show; in NAS, (1) direct, rapid recharge favoured by faults, well-drained soils and ample rainfall in uplands, (2) delayed recharge from impounded-lakes and wetlands in midlands, (3) focussed, event-based recharge in floodplains; in SC, diffuse recharge complicated by significant water-table evapotranspiration processes.

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Using stable water isotopes to identify spatial-temporal controls on groundwater recharge in two contrasting East African aquifer systems

Abstract

Bibliographical note

Keywords

Access to Document

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Impacts

Building capacity for informed groundwater policy and practice in Eastern Africa

Cite this