Shallow urban aquifers under hyper-recharge equatorial conditions and strong anthropogenic constrains. Implications in terms of groundwater resources potential and integrated water resources management strategies

B Nlend; H Celle-Jeanton; F Huneau; E Garel; S Ngo Boum-Nkot; J Etame

doi:10.1016/j.scitotenv.2020.143887

Shallow urban aquifers under hyper-recharge equatorial conditions and strong anthropogenic constrains. Implications in terms of groundwater resources potential and integrated water resources management strategies

Sci Total Environ. 2021 Feb 25:757:143887. doi: 10.1016/j.scitotenv.2020.143887. Epub 2020 Dec 2.

Authors

B Nlend¹, H Celle-Jeanton², F Huneau³, E Garel³, S Ngo Boum-Nkot⁴, J Etame⁴

Affiliations

¹ Université de Bourgogne Franche-Comté, CNRS, UMR 6249 Chrono-Environnement, 16 route de Gray, F-25030 Besançon cedex, France; University of Douala, Faculty of Sciences, P.O Box 24157, Douala, Cameroon; Cameroonian Institute for Geological and Mining Research, Hydrological Research Center, P.O Box 4110, Yaoundé, Cameroon. Electronic address: bertil.nlend@univ-fcomte.fr.
² Université de Bourgogne Franche-Comté, CNRS, UMR 6249 Chrono-Environnement, 16 route de Gray, F-25030 Besançon cedex, France.
³ Université de Corse Pascal Paoli, Département d'Hydrogéologie, Campus Grimaldi. BP 52, F-20250 Corte, France; CNRS, UMR 6134 SPE, BP 52, F-20250 Corte, France.
⁴ University of Douala, Faculty of Sciences, P.O Box 24157, Douala, Cameroon.

PMID: 33310570
DOI: 10.1016/j.scitotenv.2020.143887

Abstract

Humid equatorial regions are recognized as the least documented in term of hydrogeological functioning of aquifers despite the fact that they house a lot of developing countries and that groundwater is often the main water resource. Regarding this aspect, a study was conducted in sub-Saharan Africa, focusing on the Mio-Pliocene aquifer in Douala megacity (Cameroon) which is the rainiest city in West-Africa (about 4000 mm/year) with one of the greatest demographic growth rate of the African continent. Firstly, groundwater recharge rate has been calculated through water balance and Water Table Fluctuation methods. Results show that the aquifer is characterized by a high recharge of 600-760 mm/year. Then infiltration process and groundwater flow conditions have been examined by combining hydrogeological and isotopic methods. Rainwater infiltrated is recycled in the vadose zone through plants roots transpiration and groundwater flows with a Darcy velocity of 5 m/day. From the recharge area to the estuary, the mineralization increases controlled by anthropogenic activities and water-rocks interactions which are amplified by the residence time and accelerated by the hot and humid climate of Douala. The paper ends with the determination of natural background levels (NBLs) and threshold values (TV) of chemical components in groundwater to assess the contamination for different flow paths. This multi-proxy study and the establishment of NBLs and TV can be beneficial to improve groundwater resources management. Moreover, the conceptual model provided in this study could be used as a reference for porous aquifers submitted to high rainfall amount.

Keywords: Geochemistry; Groundwater recharge; Integrated Water Resources Management; Stable isotopes; Threshold values; Urban hydrogeology.