Assessment of Land Degradation Using Electrical Resistivity in Oil-Affected Agricultural Soils in Ogoniland, South South Nigeria

Ogoniland in Rivers State remains one of the most extensively documented zones of oil-related environmental damage in Nigeria, yet quantitative geophysical assessment of subsurface soil degradation in actively farmed areas is limited. This study assesses the depth and lateral extent of hydrocarbon contamination in oil-affected agricultural soils in Gokana Local Government Area using electrical resistivity tomography. The Wenner array was deployed along six 300-metre profiles crossing both confirmed spill sites and reference unpolluted farmland areas to enable comparative analysis. Two-dimensional resistivity models were interpreted using a contamination threshold derived from resistivity measurements in known clean soils of identical lithological composition sampled across the same profiles. Low-resistivity anomalies at shallow depths (0 to 6 metres) in affected areas contrast with the resistivity signature of clean sandy loam soils at reference sites, attributable to increased conductivity from ionic degradation products. Total petroleum hydrocarbon measurements from soil samples taken at ERT-guided locations confirm spatial correlation between geophysical anomalies and hydrocarbon presence. The extent of hydrocarbon penetration is mapped down to depths of 4 to 8 metres below surface at confirmed spill locations. The study provides geophysical evidence to support remediation planning and post-remediation monitoring as part of UNEP implementation frameworks in Ogoniland. Keywords: electrical resistivity, hydrocarbon contamination, Ogoniland, soil degradation, remediation