Degradation of groundwater quality in expanding cities in West Africa. A case study of the unregulated shallow aquifer in Cotonou
2020
Houéménou, Honoré | Tweed, Sarah | Dobigny, Gauthier | Mama, Daouda | Alassane, Abdoukarim | Silmer, Roland | Babic, Milanka | Ruy, Stephane | Chaigneau, Alexis | Gauthier, Philippe | Socohou, Akilou | Dossou, Henri-Joël | Badou, Sylvestre | Leblanc, Marc | Environnement Méditerranéen et Modélisation des Agro-Hydrosystèmes (EMMAH) ; Avignon Université (AU)-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE) | Université d’Abomey-Calavi = University of Abomey Calavi (UAC) | Gestion de l'Eau, Acteurs, Usages (UMR G-EAU) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Institut de Recherche pour le Développement (IRD)-AgroParisTech-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro ; Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro) | Centre de Biologie pour la Gestion des Populations (UMR CBGP) ; Centre de Coopération Internationale en Recherche Agronomique pour le Développement (Cirad)-Université de Montpellier (UM)-Institut de Recherche pour le Développement (IRD [Occitanie])-Institut National de Recherche pour l’Agriculture, l’Alimentation et l’Environnement (INRAE)-Institut Agro - Montpellier SupAgro ; Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro)-Institut national d'enseignement supérieur pour l'agriculture, l'alimentation et l'environnement (Institut Agro) | Laboratoire d'études en Géophysique et océanographie spatiales (LEGOS) ; Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3) ; Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Observatoire Midi-Pyrénées (OMP) ; Institut de Recherche pour le Développement (IRD)-Université Toulouse III - Paul Sabatier (UT3) ; Université de Toulouse (UT)-Université de Toulouse (UT)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Institut de Recherche pour le Développement (IRD)-Institut national des sciences de l'Univers (INSU - CNRS)-Centre National d'Études Spatiales [Toulouse] (CNES)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS) | Institut de Recherches Halieutiques et Océanologiques du Bénin (IRHOB) ; Centre de Recherches Halieutiques et Océanologiques du Bénin [Cotonou] (CRHOB) | International Chair in Mathematical Physics and Applications (ICMPA-UNESCO Chair) ; Université d’Abomey-Calavi = University of Abomey Calavi (UAC) | The authors owe much gratitude to hydrogeology laboratory of Avignon University, EPAC/LARBA and IRD/CBGP for the full financial and logistical support of this work.
International audience
اظهر المزيد [+] اقل [-]إنجليزي. Highlights• Predominant drivers of the unregulated shallow aquifer degradation in Cotonou were analysed using major ions, Cl/Br molar ratios and stables isotopes as environmental tracers. Vulnerability of this unofficial groundwater resource is due to either salinization or sewage leakage, which is temporally and spatially variable.• Increasing risks from sewage and septic tank leakage during the wet season in neighbourhoods located in discharge areas compared with increasing risk during the dry season in the recharge area.• Mixing with pond water and saline Lake Nokoué water highlight increased risks of shallow groundwater salinization during the dry and small wet seasons in discharge areas.AbstractIn Cotonou, as in many expanding West African cities, major population growth and infrastructural development has not kept up with informal settlement development onto floodable plains and marshes. The population of the slum, which makes up about 60% of the city's inhabitants, is highly disadvantaged and vulnerable to rising sea levels, flooding, sanitation and waste management issues. However, the risks associated with the use of contaminated shallow groundwater for domestic purposes are less recognised. Our study demonstrates that, in many instances, the cheaper option of the use of shallow groundwater from the coastal Quaternary aquifer for domestic purposes represents a significant risk for the poorer residents of Cotonou through the voluntary (drinking) or non-volontary (dish washing, cooking) consumption of this unmonitored and untreated water resource. In the 3 neighbourhoods surveyed, environmental tracers (major ions, Cl/Br molar ratios and stables isotopes) showed that this shallow aquifer is degraded by seawater intrusion as well as septic and sewerage contamination. In particular, the higher NOx concentrations correspond to ranges associated with sewerage and septic tank effluent pollution and the major ion concentrations and delta H-2-delta O-18 signatures showed that high salinity values are where groundwater mixes with saline Lake Nokoue water. The population using this resource from local wells should be made aware of seasonal changes in groundwater contamination and potential health risks associated with sewerage and septic tank contamination.
اظهر المزيد [+] اقل [-]الكلمات المفتاحية الخاصة بالمكنز الزراعي (أجروفوك)
المعلومات البيبليوغرافية
تم تزويد هذا السجل من قبل Institut national de la recherche agronomique