title: Origins and processes of groundwater salinization in the urban coastal aquifers of Recife (Pernambuco, Brazil): A multi-isotope approach.
abstract: In the coastal multilayer aquifer system of a highly urbanized southern city (Recife, Brazil), where groundwaters are affected by salinization, a multi-isotope approach (Sr, B, O, H) was used to investigate the sources and processes of salinization. The high diversity of the geological bodies, built since the Atlantic opening during the Cretaceous, highly constrains the heterogeneity of the groundwater chemistry, e.g. Sr isotope ratios, and needs to be integrated to explain the salinization processes and groundwater pathways. A paleoseawater intrusion, most probably the 120 kyB.P. Pleistocene marine transgression, and cationic exchange are clearly evidenced in the most salinized parts of the Cabo and Beberibe aquifers. All (87)Sr/(86)Sr values are above the past and present-day seawater signatures, meaning that the Sr isotopic signature is altered due to additional Sr inputs from dilution with different freshwaters, and water-rock interactions. Only the Cabo aquifer presents a well-delimitated area of Na-HCO3 water typical of a freshening process. The two deep aquifers also display a broad range of B concentrations and B isotope ratios with values among the highest known to date (63-68.5‰). This suggests multiple sources and processes affecting B behavior, among which mixing with saline water, B sorption on clays and mixing with wastewater. The highly fractionated B isotopic values were explained by infiltration of relatively salty water with B interacting with clays, pointing out the major role played by (palaeo)-channels for the deep Beberibe aquifer recharge. Based on an increase of salinity at the end of the dry season, a present-day seawater intrusion is identified in the surficial Boa Viagem aquifer. Our conceptual model presents a comprehensive understanding of the major groundwater salinization pathways and processes, and should be of benefit for other southern Atlantic coastal aquifers to better address groundwater management issues.
authors.affiliation: BRGM French Geological Survey, 3 Avenue Claude Guillemin, 45060 Orléans Cedex 2, France. Electronic address: l.cary@brgm.fr.
authors.forename: Lise
authors.initials: L
authors.lastname: Cary
authors.affiliation: BRGM French Geological Survey, 3 Avenue Claude Guillemin, 45060 Orléans Cedex 2, France.
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Petelet-Giraud
authors.affiliation: Institute of Geosciences, University of São Paulo, Rua do Lago, 562 Butantã, 05508-080 Sao Paulo, Brazil.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Bertrand
authors.affiliation: BRGM French Geological Survey, 3 Avenue Claude Guillemin, 45060 Orléans Cedex 2, France.
authors.forename: Wolfram
authors.initials: W
authors.lastname: Kloppmann
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Luc
authors.initials: L
authors.lastname: Aquilina
authors.affiliation: Institute of Geosciences, University of São Paulo, Rua do Lago, 562 Butantã, 05508-080 Sao Paulo, Brazil.
authors.forename: Veridiana
authors.initials: V
authors.lastname: Martins
authors.affiliation: Institute of Geosciences, University of São Paulo, Rua do Lago, 562 Butantã, 05508-080 Sao Paulo, Brazil.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Hirata
authors.affiliation: Civil Engineering Department, Federal University of Pernambuco, 50740 Recife, PE Brazil.
authors.forename: Suzana
authors.initials: S
authors.lastname: Montenegro
authors.affiliation: BRGM French Geological Survey, 3 Avenue Claude Guillemin, 45060 Orléans Cedex 2, France.
authors.forename: Hélène
authors.initials: H
authors.lastname: Pauwels
authors.affiliation: OSUR-Géosciences Rennes, Université Rennes 1 - CNRS, 35000 Rennes, France.
authors.forename: Eliot
authors.initials: E
authors.lastname: Chatton
authors.affiliation: CPRM, Brazilian Geologic Survey, Avenida Sul 2291, Recife PE, Brazil.
authors.forename: Melissa
authors.initials: M
authors.lastname: Franzen
authors.affiliation: Géo-Hyd, 101 rue Jacques Charles, 45160 Olivet, France.
authors.forename: Axel
authors.initials: A
authors.lastname: Aurouet
keywords: Boron isotopes; Brazil; Coastal aquifer; Groundwater; Recife; Salinization origins; Salinization processes; Strontium isotopes