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Communication dans un congrès
Multi-isotopes constraints on the origins and processes of groundwater salinization in coastal aquifers. Example of Recife, Northeast of Brazil
Abstract : The Recife Metropolitan Region (PE, Brazil) is a typical "hot spot" illustrating the problems of southern countries
on water issues inducing high pressures on water resources both on quantity and quality in the context of global social
and environmental changes. This study focuses on the groundwater geochemistry in a costal multilayer aquifer
and aims at investigating the sources and processes of salinization. The RMR basement is constituted by two different
Precambrian blocks separated by a large lineament area. The sedimentary fillings of the two basins present
different origins that can be distinguished by the Sr isotope composition. The northern deep Beberibe aquifer displays
very high strontium isotope ratios with a large range of values (87Sr/86Sr = 0.7102 to 0.7233) illustrating
the main continental origin of sediments whereas the southern deep Cabo aquifer showed lower 87Sr/86Sr values
(87Sr/86Sr = 0.7097 to 0.7141) indicating the contribution of the marine sedimentation dating from the Atlantic
opening. Although sulfate isotopes, Electric Conductivity and Cl contents indicate a clear mixing with seawater
for some samples of the deep Cabo and Beberibe aquifers, all 87Sr/86Sr values are above the present-day seawater
composition. This can be related to the complex local history of transgression/regression phases that induced alternatively
salinisation and freshening with gains and losses of cations and Sr, together with water-rock interactions.
Stable isotopes of the water molecule clearly evidence the local present day recharge especially within the surficial
aquifer, whereas some samples are affected by in situ evaporation processes and/or recharge with evaporated
water originating from dam used for water supply. The two deep aquifers display a high range of B concentrations
(20 to 600 g.L-1) and B isotope composition (11B = 6.7 to 68.5 h, with the highest values known to date
(63-68.5h. This suggests multiple sources and processes affecting B behavior, among which mixing with saline
water, B sorption on clays/organic matter and mixing with wastewater. Indeed, the Tertiary and Quaternary surficial
aquifers are highly contaminated with wastewater and locally salinized; here salinisation is possibly due to present
seawater intrusion.
https://hal-brgm.archives-ouvertes.fr/hal-01103181
Contributeur : Lise Cary <>
Soumis le : mercredi 14 janvier 2015 - 11:05:04
Dernière modification le : jeudi 25 juin 2020 - 11:42:07
Archivage à long terme le : : vendredi 11 septembre 2015 - 06:44:55
Contributeur : Lise Cary <>
Soumis le : mercredi 14 janvier 2015 - 11:05:04
Dernière modification le : jeudi 25 juin 2020 - 11:42:07
Archivage à long terme le : : vendredi 11 septembre 2015 - 06:44:55
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EGU2015-10320 (1).pdf
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