NDLI: Groundwater recharge/discharge in semi-arid regions interpreted from isotope and chloride concentrations in north White Nile Rift, Sudan

Content Provider	Springer Nature Link
Author	Abdalla, Osman A. E.
Copyright Year	2008
Abstract	Deuterium, oxygen-18 and chloride were analyzed for 84 samples from deep and shallow wells, precipitation and the river White Nile to investigate groundwater recharge/discharge relations in the semi-arid central Sudan. Spatial and vertical variation in isotopic signature and chloride concentration in the groundwater show similar patterns and indicate local recharge and evaporative discharge. Progressive decrease in isotopic composition along the regional groundwater flow path demonstrates aquifer continuity down the NW–SE recharge-discharge path. Isotope-heavy recharged water progressively mixes with lighter older groundwater formed during cooler and humid conditions in the late Pleistocene. However, evaporative fractionation in the flow path’s final reach in the southeast re-enriches the isotopic composition and suggests evaporative loss of groundwater as the plausible discharge mechanism. Chloride concentration increases down the gradient from the recharge area and reaches its peak in the discharge zones indicating: lack of recharge from direct infiltration down the gradient, evaporation and prolonged rock/water interaction. Head differences and increased isotopic concentration in the vicinity of the White Nile suggest recharge from the river from subsurface flow. Reduced chloride content and relatively heavier isotopic composition in the deep groundwater beneath the wadi of Khor Abu Habil indicate recharge from the streambed into the deep aquifer.Deutérium, oxygène-18 et chlorures ont été analysés pour 84 échantillons prélevés dans des puits, forages, pluies et le Nil Blanc afin de connaitre la recharge et décharge des eaux souterraines de la zone semi-aride de la région centrale du Soudan. Les variations spatiales et verticales de la signature isotopique et des concentrations en chlorures dans les eaux souterraines montrent un schéma similaire qui indique une recharge locale et une décharge par évaporation. La diminution progressive de la composition isotopique le long des lignes de flux régionales démontre une continuité des processus de recharge et décharge selon un axe NW-SE. Les eaux enrichies isotopiquement se mêlent progressivement aux eaux plus appauvries car rechargées sous les conditions plus humides et froides du Pléistocène supérieur. Toutefois, le fractionnement isotopique dû à l’évaporation des eaux le long des lignes de flux entraîne à l’aval, au sud-est, un ré-enrichissement de la composition isotopique des eaux qui suggère que la perte par évaporation est une composante importante de la décharge. Les concentrations en chlorures augmentent en allant vers l’aval et atteignent un maximum dans la zone de décharge indiquant par là: une absence de recharge par infiltration directe le long des lignes de flux, une évaporation et interaction eau-roche importante. Les changements des niveaux piézométriques et l’augmentation des teneurs isotopiques au voisinage du Nil Blanc suggèrent une recharge par la rivière des horizons superficiels. Une diminution des concentrations en chlorures et une composition isotopique relativement plus enrichie dans les niveaux profonds de l’aquifère sous le wadi Khor Abu Habil indiquent une recharge depuis le lit de la rivière vers l’aquifère profond.Para investigar las relaciones recarga/descarga en la región semi-árida central del Sudán fueron analizados deuterio, oxígeno-18 y cloruro, a partir de 84 muestras de pozos profundos y someros, de las precipitaciones y del río Nilo Blanco. La variación espacial y vertical de la señal isotópica y la concentración de cloruros en las aguas subterráneas muestran patrones similares e indican la recarga local y la descarga por evaporación. La disminución progresiva de la composición isotópica a lo largo del flujo regional del agua subterránea demuestra la continuidad del acuífero en la trayectoria de la recarga - descarga hacia el NW-SE. Los isótopos pesados del agua recargada se mezclan progresivamente con los más livianos de aguas subterráneas más antiguas formadas en condiciones más frías y húmedas en el Pleistoceno tardío. Sin embargo, el fraccionamiento por evaporación en el trayecto final del flujo en el sudeste produce un re-enriquecimiento de la composición isotópica y sugiere que la pérdida por evaporación es un mecanismo aceptable de la descarga de las aguas subterráneas..La concentración de cloruro aumenta en coincidencia con el gradiente de flujo desde la zona de recarga y alcanza su pico en las zonas de descarga. Ello indica: la falta de recarga a partir de infiltración directa en el sentido del gradiente de flujo subterráneo, evaporación y prolongada interacción roca/agua. Las diferencias de carga e incremento en la concentración isotópica en las inmediaciones del Nilo Blanco sugieren la recarga desde el río hacia el flujo subterráneo. Los contenidos reducidos de cloruro y composición isotópica relativamente más pesada en las aguas subterráneas profundas debajo del uadi de Khor Abu Habil indican una recarga desde el cauce hacia el acuífero profundo.Analisou-se o deutério, o oxigénio 18 e o cloreto em 84 amostras provenientes de poços profundos e pouco profundos, da precipitação e do rio Nilo Branco para investigar as relações de recarga/descarga na região semi-árida do Sudão central. A variação espacial e vertical da assinatura isotópica e a concentração de cloreto na água subterrânea mostram padrões similares e apontam para recarga local e descarga evaporativa. A diminuição progressiva da composição isotópica ao longo do percurso de escoamento subterrâneo regional demonstra a continuidade dos aquíferos ao longo do curso de recarga/descarga de orientação NW-SE. A água recarregada com isótopos pesados mistura-se progressivamente com a água subterrânea mais leve e mais antiga que se formou em condições mais frescas e húmidas no final do Plistocénico. No entanto, a fraccionação evaporativa no percurso final de fluxo, a sudeste, re-enriquece a composição isotópica, sugerindo como mecanismo de descarga plausível a perda evaporativa de água subterrânea. A concentração de cloreto aumenta para jusante a partir da área de recarga e atinge o máximo nas zonas de descarga, indicando, no mesmo sentido, défice de recarga por infiltração directa, evaporação e interacção água-rocha prolongada. As diferenças de potencial hidráulico e o aumento da concentração isotópica nas proximidades do rio Nilo Branco sugerem que haja recarga a partir do rio e do seu escoamento sub-superficial. Os teores reduzidos de cloreto e a composição isotópica relativamente mais pesada na água subterrânea profunda sob o wadi Khor Abu Habil indicam recarga a partir do leito para o aquífero profundo.
Starting Page	679
Ending Page	692
Page Count	14
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	17
Issue Number	3
e-ISSN	14350157
Language	Portuguese
Publisher	Springer-Verlag
Publisher Date	2008-11-15
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Groundwater recharge/water budget Stable isotopes Chloride Evapotranspiration Sudan Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Geology Hydrogeology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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