Stable Isotope Assessment of Groundwater Recharge and Climatic Sensitivity in the N’Kappa Coastal Aquifer, Cameroon

Abstract

Groundwater in the N’Kappa area of the Douala Basin serves as a vital water source for domestic and agricultural use in a region where centralized water supply systems remain inadequate. With rapid population growth, expanding settlements, and the growing impacts of climate change, there's increasing pressure on this vital resource. Despite the importance of groundwater in this coastal basin, little is known about its recharge dynamics, limiting effective management and policy development. This study addresses this gap by applying stable isotope techniques (δ¹⁸O and δ²H) to characterize the recharge mechanisms and environmental changes of the N’Kappa Coastal Aquifer. Twenty groundwater samples were collected during the rainy season and analyzed using Cavity Ring-Down Spectroscopy. The isotopic composition revealed a narrow range (δ¹⁸O: –3.61 to –2.73‰; δ²H: –12.8 to –4.7‰) and high d-excess values (12.96 to 17.13‰), indicating recharge from Atlantic-derived precipitation under humid conditions with limited evaporative loss. The Local Meteoric Water Line (LMWL: δ²H = 8.161δ¹⁸O + 12.95) closely mirrors the Global Meteoric Water Line, indicating rapid infiltration during high-intensity rainfall events. Isotopic homogeneity across samples suggests a young, well-mixed aquifer with short residence times. These findings indicate the aquifer is influenced by local climate patterns and may be vulnerable to future shifts in rainfall. The study underscores the need for integrated groundwater management strategies that incorporate long-term isotope monitoring, protection of recharge zones, and sustainable land-use planning to mitigate contamination risks and safeguard water resources in the N’Kappa area.