TY - JOUR
T1 - Using stable water isotopes to identify spatial-temporal controls on groundwater recharge in two contrasting East African aquifer systems
AU - Oiro, Samson
AU - Comte, Jean-Christophe
AU - Soulsby, Chris
AU - Walraevens, Kristine
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.
PY - 2018/6/6
Y1 - 2018/6/6
N2 - 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.
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.
KW - Groundwater recharge
KW - Stable isotopes
KW - Aquifer systems
KW - Meteoric water line
KW - Evaporation effect
U2 - 10.1080/02626667.2018.1459625
DO - 10.1080/02626667.2018.1459625
M3 - Article
VL - 63
SP - 862
EP - 877
JO - Hydrological Sciences Journal
JF - Hydrological Sciences Journal
SN - 0262-6667
IS - 6
ER -