Chemical and Isotopic Characterization of Water Resources in the Fractured Crystalline Aquifers of the Bafia area, Centre Region -Cameroon: Implications for Water Management

The sustainable management of groundwater resources in the Bafia crystalline aquifers is challenging owing to their complex hydrogeological characteristics, limited understanding of the aquifer system, increasing demand for potable water and vulnerability to nitrate contamination. This study focuses on the chemical and isotopic characterization of water resources in the crystalline aquifers of Bafia, aiming to understand the hydrogeochemical processes controlling water composition. A total of 117 water samples from boreholes, shallow hand-dug wells, rivers, and springs (57 for wet and 60 for dry season) were analyzed for major ions by IC system; trace elements by ICP-MS; stable isotopes (δ¹⁸O, δ²H) by CRDS; tritium by liquid scintillation and dual nitrogen isotopes (δ15N-NO3 and δ¹⁸O-NO3) by Laser isotope spectrometry using TiCl3 extraction. Hydrochemical data were processed using multivariate statistical methods and graphical tools such as Piper and Gibbs diagrams, stable isotopic results were compared with the Global Meteoric Water Line (GMWL) and the Yaounde Local Meteoric Water Line (YLMWL), while nitrate contamination was assessed using the Kendall diagram. Results reveal mainly Ca-Mg-HCO3 water type, generally acidic to neutral (3.2 < pH < 7.4) and moderately mineralized (30 < EC < 2220 µS/cm), indicating active and rapid recharge, with minimal changes prior to infiltration. Two main factors influence water quality, namely: natural factors (rock/mineral weathering and dissolution, ion exchange, soil leaching, topography) and anthropogenic activities (manure/fertilizer, untreated wastes disposal, leaky/poorly constructed pit latrines, well chlorination). Groundwater and especially surface water, is excellent for drinking (WQI < 25 and HPI < 100) and irrigation. Isotopic signatures reveal recharge from recent meteoric water, with minor evidence of evaporation and localized mixing processes. More than 70% samples demonstrate a mixture of sub-modern and recently recharged water, with some protected areas identified. High NO3/Cl ratios and δ15N-NO3 (>10%) insinuate a mixture of urban and agricultural nitrate contamination sources. These findings provide critical insights into the dynamics of the crystalline aquifer system and emphasize the need for integrated water management strategies that account for both natural hydrogeological conditions and increasing anthropogenic pressures in the Bafia area.