Isotope characteristics of meteoric water and groundwater in the Sahelo‐Sudanese zone

Abstract

The stable isotopic concentration (18O and 2H) of water in phreatic aquifers in the Sahelo‐Sudanese zone of Africa is representative of the original mean rainfall contributing to ground water recharge. The isotopic decrease of 18O in the rainwater and groundwater (−0.084 ‰ 100 km−1) showed an east‐west gradient. This suggests a supply of water vapor transported by the zonal flows East African Jet, Tropical Easterly Jet, and Easterly Waves, thus increasing the contribution from the evaporating surfaces of the Indian Ocean in relation to that of the Guinean monsoon. The gradient also indicates the importance of atmospheric recycling of continental water through evapotranspiration. A model of conservation of the isotopic masses is presented which takes into account the return of continental vapor toward the rain‐giving clouds. The remaining fraction of water vapor during the east‐west transit between Djibouti and Dakar is thus determined by evapotranspiration.

Variation in stable isotope ratios of monthly rainfall in the Douala and Yaounde cities, Cameroon: local meteoric lines and relationship to regional precipitation cycle

“…The observed lack of continental effect is probably due to the added inland moisture from vegetation and numerous water bodies in the region to precipitation. This finding confirms the lack of continental effect that has previously been observed in Sub-Saharan Africa (Joseph et al 1992;Taupin et al 2000). Isotopically enriched and depleted rains were mainly associated with precipitation during the dry seasons (pre-and post-monsoons) and rainy seasons (monsoon), respectively.…”

The use of isotopes and environmental tracers in subsurface hydrology

“…Examples include the Midwestern studies by Siegel (1990 and The utility of isotopic tracers in applied research on water quality problems is beginning to be widely appreciated. Joseph et al (1992) have applied stable isotopes to infer the relationship between atmospheric sources of water vapor and the resultant groundwater recharge (or lack of it) in the Sahel. Simpson and Herczeg (1991) have used stable isotope enrichment as a method of investigating the sources of the salinization that is afflicting the Murray River Basin in Australia.…”

Groundwater flow dynamics in the complex aquifer system of Gidabo River Basin (Ethiopian Rift): a multi-proxy approach

“…The description of the hydrochemical evolution given in the preceding suggests that the deeply circulating groundwater is recharged in the upper catchment (highland and escarpment) and chemically altered along its flow path into the rift floor. (Sonntag et al 1979;Joseph et al 1992;Rozanski et al 1996;Darling and Gizaw 2002). Kebede (2004) and Levin et al (2009) confirmed that the dexcess is attributed to the mixing of recycled moisture from continental source and direct moisture from the Indian Ocean.…”