Longitudinal Assessment of Ecosystem Resilience Following Oil Spill Remediation in the Niger Delta, South South Nigeria: A 15-Year Perspective

Ecosystem resilience following large-scale oil contamination and subsequent remediation in the Niger Delta remains deeply contested, with disagreements between industry claims of successful recovery and community and scientific reports of persistent ecological impairment. This study provides the first long-term longitudinal assessment of ecosystem resilience across a 15-year period at three major oil spill and remediation sites in the Niger Delta, using a standardised multi-trophic monitoring protocol applied at two-year intervals. Ecological indicators assessed included mangrove canopy recovery, benthic macroinvertebrate community reestablishment, estuarine fish diversity, sediment total petroleum hydrocarbon depletion, and soil microbial functional diversity. Resilience was quantified using dynamic stability metrics including resistance, recovery rate, and engineering resilience derived from time-series data. Results reveal highly heterogeneous recovery trajectories among sites and ecological indicators. Sediment petroleum hydrocarbon concentrations declined steadily at all sites but remained above pre-spill background levels after 15 years at one site. Mangrove canopy recovered to 62 percent of reference cover on average but with persistent compositional differences. Benthic macroinvertebrate richness recovered to 78 percent of reference values while functional diversity lagged behind, suggesting incomplete functional recovery despite apparent taxonomic recovery. Fish community composition remained detectably altered from reference assemblages at all sites. The study challenges the adequacy of current remediation standards and provides a 15-year ecological data archive that establishes scientifically defensible recovery benchmarks for future Niger Delta spill assessments. Keywords: ecosystem resilience, oil spill remediation, Niger Delta, long-term monitoring, recovery trajectory.