Hydrological budgets and study of the groundwater recharge of 3 lake-aquifer system within the lake Chad basin using a multi-tracers approach (δ18O, δ2H, 36Cl, 14C)
Description
Surface water and groundwater are threatened all over the Sahel and the Sahara, because of over-exploitation, population growth and climate change that are limiting groundwater sustainable access. Lake Chad Basin, located in the middle of the Sahel zone, cannot avoid these problems. The aim of this work is to understand the hydrological functioning of three lake systems within the basin and the hydrogeological functioning of the associated aquifers with particular emphasis on the modern and past recharge. We have coupled information obtained from the stable isotopes of water, 36Cl and 14C. The three studied lakes are evenly spaced from South to North with an increasingly arid climate toward the North. A rst water budget has been calculated for the lakes Iro by coupling stables isotopes data with satellite imagery. We have calculated the influx and out-flux and shown that these lakes are 'open' i.e. with a surface or an underground out-flux. The aquifer recharge is modern, since we observed thermonuclear 36Cl in the groundwater, although we do not exclude a few hundred years old recharge for some parts of Lake Fitri's aquifer. The Ounianga Lakes are located in the Saharan part of the Lake Chad basin, where they form oasis systems fed by the Nubian Sandstone Aquifer. They are split into two distinct systems: Ounianga Kebir and Ounianga Serir with two different hydrologic functioning. The Serir part is a chain of lakes with an increasing salinity towards the central lake, while the lakes of the Kebir system are independent from each other. By contrast with Iro and Fitri, we did not observe thermonuclear 36Cl in these lakes and groundwaters. On the other hand, these samples do not show any evidence of radioactive decay of 36Cl as observed by previous studies in the Egyptian part of the aquifer. 14C data enabled us to estimate an age of recharge around 10 000 years ago. (author)
Abstract (French)
Les ressources en eau de surface et souterraine du Sahel et du Sahara sont sous pression: surexploitation, augmentation demographique et changement climatique sont autant de facteurs menacant l'acces durable a ces ressources. Le bassin du lac Tchad situe au coeur de la zone sahelienne n'echappe pas a ces problematiques. L'objectif de ce travail est de comprendre le fonctionnement hydrologique de 3 grands systemes lacustres de ce bassin ainsi que le fonctionnement des aquiferes associes et plus particulierement leur processus de recharge. Pour cela une approche geochimique a ete mise en place en couplant l'analyse des isotopes stables de la molecule d'eau, du 36Cl et du 14C. Les trois lacs etudies se repartissent du Sud au Nord du pays sous un climat qui s'aridie vers le nord. L'etude des isotopes stables couplee a de l'imagerie spatiale a permis dans un premier temps d'etablir un premier bilan hydrologique des lacs Iro et Fitri. Nous calculons des flux d'entree et de sortie et montrons leur caractere 'ouvert' avec un exutoire en surface ou souterrain. La recharge de leurs aquiferes respectifs est plutot recente: presence de 36Cl thermonucleaire dans les eaux souterraines, meme si une recharge de plusieurs centaines d'annees n'est pas exclue pour l'aquifere autour du lac Fitri. Les lacs Ounianga situes en milieu saharien forment des oasis alimentes uniquement par le systeme aquifere des gres de Nubie. Divises en deux systemes de lacs: Ounianga Kebir et Ounianga Serir, ils presentent des fonctionnements hydrologiques differents. Le systeme Serir fonctionne en chaine de lacs avec une augmentation progressive de la salinite vers le lac central, alors que les lacs du systeme Kebir, fonctionnent plus ou moins independamment les uns des autres. Les donnees 36Cl n'indiquent pas de 36Cl thermonucleaire, ni de decroissance radioactive comme observe dans la partie egyptienne de l'aquifere des Gres de Nubie. En revanche les donnees 14C ont permis de dater une recharge du systeme aquifere il y a 10 000 ans. (auteur)
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Additional details
Additional titles
- Original title (French)
- Bilans hydrologiques et etude de la recharge de trois systemes lac-aquifere du Bassin du Lac Tchad par une approche geochimique multi traceurs (δ18O, δ2H, 36Cl, 14C)
Publishing Information
- Imprint Pagination
- 164 p.
- Report number
- FRNC-TH--10999
INIS
- Country of Publication
- France
- Country of Input or Organization
- France
- INIS RN
- 51079055
- Subject category
- S58: GEOSCIENCES; S54: ENVIRONMENTAL SCIENCES;
- Resource subtype / Literary indicator
- Thesis
- Descriptors DEI
- AQUIFERS; CARBON 13; CARBON 14; CARBON CYCLE; CHAD; CHLORINE 36; DEUTERIUM; GROUNDWATER RECHARGE; HYDROLOGY; ISOTOPE DATING; ISOTOPE RATIO; LAKES; OXYGEN 18; RESIDENCE HALF-TIME; TRACER TECHNIQUES; WATERSHEDS
- Descriptors DEC
- AFRICA; AGE ESTIMATION; BETA DECAY RADIOISOTOPES; BETA-MINUS DECAY RADIOISOTOPES; BETA-PLUS DECAY RADIOISOTOPES; CARBON ISOTOPES; CHLORINE ISOTOPES; DEVELOPING COUNTRIES; DIMENSIONLESS NUMBERS; ELECTRON CAPTURE RADIOISOTOPES; EVEN-EVEN NUCLEI; EVEN-ODD NUCLEI; HYDROGEN ISOTOPES; ISOTOPE APPLICATIONS; ISOTOPES; LIGHT NUCLEI; NUCLEI; ODD-ODD NUCLEI; OXYGEN ISOTOPES; RADIOISOTOPES; STABLE ISOTOPES; SURFACE WATERS; YEARS LIVING RADIOISOTOPES
Optional Information
- Notes
- 278 refs.; Available from the INIS Liaison Officer for France, see the INIS website for current contact and E-mail addresses