干旱区生态环境知识资源中心

The Nubian Sandstone (NSS) aquifer of northeast Africa is believed to have been recharged in previous wet climatic periods in the Quaternary Period. While this is largely true, we show using the Sinai Peninsula as our test site that the aquifer is locally receiving modern recharge under the current dry climatic conditions. The validity of the advocated model was tested using geophysical (conventional electrical resistivity [ER]) and isotopic (O, H) data, and estimates for modern recharge were obtained using continuous rainfall-runoff modeling over the period 1998-2007. Interpretations of ER profiles are consistent with the presence of unconfined NSS aquifers flooring recharge areas at the foothills of the crystalline basement in Sinai at Baraga (thickness: 20 to >188 m; resistivity: 16-130 Omega m) and Zalaga (thickness: 27 to >115 m; resistivity: 3-202 Omega m). The isotopic composition (delta D: -22.7 to -32.8 parts per thousand; delta O-18: -4.47 to -5.22 parts per thousand) of groundwater samples from wells tapping the NSS aquifer underlying recharge areas is consistent with mixing between two endmembers: (1) fossil groundwater with isotopic compositions similar to those of the Western Desert NSS aquifer (delta D: -72 to -81 parts per thousand; delta O-18: -10.6 to -11.9 parts per thousand), and (2) average modern meteoric precipitation (delta D: -9.84 parts per thousand; delta O-18: -3.48 parts per thousand) in Sinai, with the latter endmember being the dominant component. A first-order estimate for the average annual modern recharge for the NSS aquifer was assessed at similar to 13.0 x 10(6) m(3)/yr using the SWAT (Soil Water Assessment Tool) model. Findings bear on the sustainable exploitation of the NSS aquifer, where the aquifer is being locally recharged, and on the exploitation of similar extensive aquifers that were largely recharged in previous wet climatic periods but are still receiving modest modem meteoric contributions. (C) 2011 Elsevier B.V. All rights reserved.