Groundwater Systems, Aquifer Characterization, and Sustainability Challenges in Nigeria: A Scoping Review of Hydrogeological and Geophysical Investigations (2000–2026)

ABSTRACT: Groundwater represents one of the most important freshwater resources in Nigeria and serves as a major source of water for domestic, agricultural, and industrial activities. This scoping review synthesizes existing knowledge on groundwater systems, aquifer characterization, hydrogeophysical investigations, groundwater quality, and sustainability challenges across different hydrogeological environments in Nigeria. The review adopted the PRISMA-ScR framework and analyzed peer-reviewed studies published between 2000 and 2026, retrieved from Scopus, Web of Science, Google Scholar, ScienceDirect, and SpringerLink databases. The findings revealed substantial hydrogeological variability associated with the Basement Complex terrains, sedimentary basins, Coastal Plain Sands, and alluvial aquifer systems. Vertical Electrical Sounding (VES), Electrical Resistivity Tomography (ERT), hydrochemical analysis, GIS integration, and remote sensing emerged as the dominant groundwater investigation techniques. The review further identified increasing groundwater quality deterioration resulting from salinity intrusion, industrial pollution, oil spill contamination, excessive groundwater abstraction, and climate variability. Coastal aquifers within the Niger Delta, Lagos, and Akwa Ibom regions were found to be particularly vulnerable to seawater intrusion and hydrocarbon contamination. Despite increasing groundwater studies, major gaps remain in long-term monitoring, integrated hydrogeophysical investigations, and national groundwater database development. The study emphasizes the need for integrated groundwater management, sustainable policy frameworks, climate-resilient groundwater assessment approaches, and interdisciplinary research strategies to support long-term groundwater sustainability and water security in Nigeria.