Vulnerability mapping as a tool to foster groundwater protection in areas subject to rapid population expansion: The case study of Abuja Federal Capital Territory (Nigeria)

Abuja Federal Capital Territory (FCT; Nigeria). Rapid population growth has led to significant land use changes, with potential negative impacts on groundwater quality. However, the lack of understanding of hydrogeological settings, often due to limited data availability, is one of the main obstacles to sound planning in rapidly changing environments. To assess the specific groundwater vulnerability to nitrate, a DRASTIC-LU model was applied, combining the land use data from the last 20 years with the intrinsic aquifer vulnerability. This study represents the first attempt to assess aquifer vulnerability in the region. Results show that the Abuja FCT has been affected by a dramatic change in land use with an increase in urbanized and agricultural areas and may induce nitrate contamination in groundwater. Currently, several wells in the region are showing nitrate concentrations that exceed the statutory limit for drinking purposes. The comparison of DRASTIC-LU results with nitrate concentrations shows that the highest concentrations are found in urban/peri-urban areas. Although fertilizers are generally considered to be the main source of nitrate contamination, these results suggest a possible mixed (urban and agricultural) pollution origin. This investigation therefore represents a starting point for future nitrate monitoring assessments and for supporting decision makers with adequate information for urban planning in view of the expected population growth in the area.