NDLI: Tracing stable isotope values from meteoric water to groundwater in the southwestern part of the Chad basin

Content Provider	Springer Nature Link
Author	Goni, I. B.
Copyright Year	2005
Abstract	The southwestern Chad basin is a semi-arid region with annual rainfall that is generally less than 500 mm and over 2,000 mm of evapotranspiration. Surface water in rivers is seasonal, and therefore groundwater is the perennial source of water supply for domestic and other purposes. Stable isotope has been measured for rainwater, surface water and groundwater samples in this region. The stable isotope data have been used to understand the inter-relationships between the rainwater, surface water, shallow and deep groundwater of this region. This is being used in a qualitative sense to demonstrate present day recharge to the groundwater. Stable isotope in rainwater for the region has an average value of –4‰ δ$^{18}$O and –20‰ δ$^{2}$H. Surface water samples from rivers and Lake Chad fall on the evaporation line of this average value. The Upper Zone aquifer water samples show stable isotope signal with a wide range of values indicating the complex character of the aquifer Zone with three distinguishable units. The wide range of values is attributable to waters from individual unit and/or mixture of waters of different units. The Middle and Lower aquifers Zones’ waters show similar stable isotopes values, probably indicating similarity in timing and/or mechanism of recharge. These are palaeowaters probably recharged under a climate that is different from today. The Upper Zone aquifer is presently being recharged as some of its waters show stable isotope compositions similar to those of average rainfall waters of the region.Le Sud-Ouest du bassin du Tchad est une région semi-aride, caractérisée par une pluviométrie annuelle généralement inférieure à 500 mm et une évapotranspiration supérieure à 2000 mm. Les eaux de surface, dans les rivières, sont saisonnières, et dés lors l’eau souterraine est par excellence la ressource d’eau pérenne, pour, entre autres, l’usage domestique. Les isotopes stables ont été mesurés dans des échantillons d’eau de pluie, d’eaux de surfaces et d’eaux souterraines de la région. Les mesures d’isotopes stables ont été utilisées pour comprendre la relation entre les eaux de pluie, les eaux de surface, les eaux souterraines de surface et profondes. Ceci a été utilisé d’une manière qualitative, pour évaluer la recharge actuelle de l’eau souterraine. Les isotopes stables de l’eau de pluie sur la région ont une valeur moyenne de −4‰ δ$^{18}$0 et −20‰ δ$^{2}$H. Les eaux de surface des rivières et du Lac Tchad se trouvent sur la ligne d’évaporation résultant de cette valeur moyenne. La partie supérieure de l’aquifère présente un signal hétérogène en isotope stable, ce qui évoque le caractère complexe de la zone aquifère, avec trois unités distinguables. La plus part des valeurs sont attribuées à des eaux provenant des unités individuelles, et/ou à un mélange de ces différentes unités. Les zones aquifères intermédiaires et plus profondes montrent des valeurs en isotopes stables similaires, indiquant des similitudes probables sur la durée et le mécanisme de recharge. Ce sont probablement des paléo-eaux souterraines marquées par la recharge à l’époque où les climats étaient différents de maintenant. La zone supérieure de l’aquifère est présentement rechargée, comme le montre le signal isotopique de certains échantillons, similaire au signal des eaux de pluies régionales.La cuenca suroeste de Chad es una región semiárida con lluvia anual generalmente menos de 500 mm y por encima de 2,000 mm de evapotranspiración. El agua superficial en los ríos es estacional y por lo tanto el agua subterránea es la fuente perenne de abastecimiento de agua para uso doméstico y otros propósitos. Se han medido isótopos estables en agua de lluvia, agua superficial y muestras de agua subterránea en esta región. Los datos de isótopos estables se han utilizado para entender las interrelaciones entre el agua de lluvia, agua superficial, y agua subterránea somera y profunda de esta región. Esto se ha utilizado en un sentido cualitativo para demostrar la recarga actual a el agua subterránea. Los isótopos estables en agua de lluvia para la región tienen un valor promedio de –4‰ δ$^{18}$0 y –20‰ δ$^{2}$. Las muestras de agua superficial de los ríos y el Lago Chad caen sobre la línea de evaporación de este valor promedio. Las muestras de agua del acuífero de la Zona Superior muestran señales de isótopos estables con un amplio rango de valores indicando el carácter complejo de la zona acuífera que tiene tres unidades distinguibles. El amplio rango de valores se atribuye a aguas provenientes de unidades individuales y/o mezcla de agua de diferentes unidades. Las aguas de la zona Media e Inferior de los acuíferos muestran valores similares de isótopos estables, indicando probablemente similitud en tiempo y/o mecanismo de recarga. Estas son paleoaguas probablemente recargadas bajo un clima que es diferente al actual. El acuífero de la Zona Superior está siendo recargado actualmente ya que algunas de sus aguas muestran composiciones de isótopos estables similares a las de agua de lluvia promedio de la región.
Starting Page	742
Ending Page	752
Page Count	11
File Format	PDF
ISSN	14312174
Journal	Hydrogeology Journal
Volume Number	14
Issue Number	5
e-ISSN	14350157
Language	English
Publisher	Springer-Verlag
Publisher Date	2005-11-18
Publisher Institution	International Association of Hydrogeologists
Publisher Place	Berlin, Heidelberg
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Stable isotope Rainwater Groundwater recharge Chad basin Waste Water Technology Water Pollution Control Water Management Aquatic Pollution Hydrogeology Geology
Content Type	Text
Resource Type	Article
Subject	Earth and Planetary Sciences Water Science and Technology

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