Assessing the Impacts of Oil Spills on Soil Macrofauna Diversity in Affected Communities of Rivers State

Oil spill contamination of terrestrial soils in the Niger Delta region has extensive ecological consequences beyond the visible surface vegetation death, including disruption of soil faunal communities that mediate organic matter decomposition and nutrient cycling. This study assesses the impacts of oil spill contamination on soil macrofauna diversity and community composition in three oil-affected communities in Rivers State, compared with three uncontaminated reference sites. Soil macrofauna were sampled using the TSBF (Tropical Soil Biology and Fertility) protocol, with monolith extraction to 30-centimetre depth at twenty plots per site. Total petroleum hydrocarbon concentrations were measured in soil samples from each plot to quantify contamination intensity. Macrofauna were identified to family level, counted, and classified by functional group. Diversity indices and ordination analysis were used to characterise community differences between contaminated and reference sites. Results demonstrate a 74% reduction in total macrofauna abundance and a 61% reduction in family richness at highly contaminated sites compared to clean reference soils. Earthworm abundance showed the sharpest decline, with virtual absence from soils with total petroleum hydrocarbon concentrations above 5,000 mg/kg. Termite diversity was moderately affected, while Diplopoda showed greater contamination tolerance. Ordination clearly separated community composition between contaminated and reference sites, with functional group composition shifting from a decomposer-dominated to a scavenger-tolerant assemblage at contaminated locations. Recovery of macrofauna communities at previously spilled and nominally remediated sites remained poor, suggesting inadequate remediation depth. Recommendations emphasise mandatory deep soil remediation protocols for oil spill response in Rivers State. Keywords: oil spill, soil macrofauna, biodiversity, Rivers State, contamination