Abstract

Illegal crude oil bunkering and artisanal refining are becoming the leading cause of oil spill in the Niger Delta. In this study, we used standard physicochemical and microbiological methods to study a freshwater wetland in Apoi Creek, Bayelsa State that was affected by oil spill and an adjacent unpolluted site. The results show that both study areas are slightly acidic with low salinity and macronutrients particularly nitrate, phosphate and potassium. Heavy metals (zinc, lead and nickel) occurred in traces in unpolluted soil, which were generally below 0.1 mg/kg in both strata, but significantly higher levels (P<0.05) of zinc and lead occurred in the polluted soil. In the topsoil strata, TOC, TOM and ETPH were 0.60±0.01%, 1.03±0.64% and 85±7.07 mg/kg in the unpolluted soil but 5.12±0.02%, 8.80±0.03% and 1,404±1.41 mg/kg respectively in the polluted soil (P<0.05). In the subsoil strata, the trend was similar, but with higher concentrations. In the topsoil, THB was 1.21±2.12×108 cfu/g in the unpolluted site and 9.40±4.95×108 cfu/g in the polluted site (P<0.05). In the subsoil, they were also in the order of 108 (P>0.05). In the topsoil strata, HUB density was 5.65±9.19×107 cfu/g in the unpolluted site and 8.95±0.71×108 cfu/g in the polluted soil (P>0.05). In the subsoil, the population density of HUB in the unpolluted site was 4.25±0.71×107 cfu/g, which was significantly lower (P<0.05) than the 8.20±5.66×108 recorded in the polluted site. The dominant bacteria identified using molecular method based on 16S rDNA gene sequencing include Bacillus altitudinis, Fictibacillus macauensis, Micrococcus luteus and Enterobacter chengduensis. We conclude that the oil spill impacted the wetland via increased hydrocarbons and heavy metal content.

Key words: Heterotrophic bacteria, Hydrocarbon utilizers, Illegal bunkering, Niger Delta, Oil exploration, Oil spill