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Journal of Environmental Hydrology
ISSN 1058-3912 |
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Electronic Journal of the International Association for
Environmental Hydrology
JEH Volume 16 (2008), Paper 6 Posted January 31, 2008 ISOTOPIC PROPERTIES OF RAINFALL AND GROUNDWATER RESOURCES IN THE IULLEMEDEN BASIN, WEST AFRICA
Y. Sokona ABSTRACT The isotopic composition of rainfall sampled at Niamey, Niger, between 1992 and 1999 reveals a close correlation with the climatic variables of relative humidity and mean monthly air temperature. The isotopic signature of rainfall indicates the impact of climatic variability in the Iullemeden basin. The isotopic variation of precipitation over that basin confirms the rainfall quantity effect as well as the continental effect. Lighter precipitation over the Iullemeden basin displays a more enriched isotopic composition whereas more depleted isotope values are observed in heavier precipitation. The variation can be related to evaporation at the time of rainfall. The variation of the annual weighted mean of d18O in 1992 and 1999 rainfall points out the unusual role of both altitude and quantity effects. The continental effect which normally leads to a depletion of heavy isotopes in rainfall owing to lower temperatures of condensation is also observed. The isotopic characteristic of groundwater of the Sokoto basin, a subbasin of the Iullemeden basin, shows a good relation between d18O and d2H. This relation suggests the same origin of vapor and the same processes of condensation. The low slope and the position of data points below the GMWL shows the influence of evaporation. The rather depleted values of d18O and d2H for the groundwater taken from Goronyo, Taloka, and Amahali boreholes tapping the Wurno Formation of Cretaceous age reflects paleogroundwater recharged during the cooler climate of the Pleistocene era. Reference: Sokona, Y., S. Al-Gamal, and A. Dodo. 2008. Isotopic properties of rainfall and groundwater resources in the Iullemeden basin, West Africa. Journal of Environmental Hydrology, Vol. 16, Paper 6. CONTACT: S. Al-Gamal Sahara and Sahel Observatory Tunis Tunisia E-mail: samoreg@yahoo.co.uk |
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