Seasonal and Spatial Variability of Nitrate Concentration in Aquifers of Makurdi Metropolis and Its Environs, North Central Nigeria

This study examined seasonal and spatial variation of nitrate concentrations in aquifers of Makurdi metropolis and environs, with implications for drinking water quality. Twenty-five boreholes were purposively selected to represent major settlements and aquifer types, and samples were collected in the wet (September 2024) and dry (April 2025) seasons using the grab method. Coordinates at each sampling point were recorded with GPS, potential pollution sources documented, and samples analysed for nitrate using spectrometric method in line with APHA (2017) and WHO standards. Spatial variability was mapped with ArcGIS 10.8.2 using Inverse Distance Weighted (IDW) interpolation. Results showed seasonal variation, with mean nitrate levels of 24.26 mg/L in the wet season and 22.27 mg/L in the dry season. While most boreholes complied with the Nigerian Standard for Drinking Water Quality (50 mg/L), exceedances were observed in BH5 (54.4 mg/L) and BH11 (52.1 mg/L) constituting 8% during the wet season, and in BH11 (51.1 mg/L) constituting 4% during the dry season. Elevated concentrations clustered in urban and peri-urban zones such as Akpehe, BSU, Logo, and Agan, largely due to agriculture, sanitation lapses, and waste disposal, whereas deeper aquifers (>100 m) generally showed lower levels. The findings highlight localised nitrate risks, underscoring the need for groundwater protection, improved sanitation, controlled fertilizer use, and safe alternative water sources.