Bacteriological, Chemical and Soil Enzyme Activity Profile of Coastal Wetland Soils Exposed to Crude Oil Exploration in Akwa Ibom State, Nigeria

Abstract

Coastal wetland soils exposed to crude oil exploration activities were assessed using microbiological and chemical procedures in the wet and dry seasons. The bacteria isolated from the impacted wetland soils included species of the genera Acinetobacter, Alcaligenes, Citrobacter, Azotobacter, Bacillus, Cellulomonas, Flavobacterium, Micrococcus, Proteus, Pseudomonas, Sarcina, Serratia and Staphylococcus. In addition, species of the genera Nitrobacter, Nitrosomonas and Rhizobium were isolated from the non-impacted soils. Total heterotrophic bacterial counts (THBC) in the wet and dry seasons ranged from 7.1 ± 0.4 to 8.6 ± 0.2 Log₁₀CFU g‾¹ and 3.7± 0.04 to 5.4 ± 0.1 Log₁₀CFU g‾¹ for the control and impacted soils respectively. The counts in control was 1.6 to 1.9 times higher than the impacted soil and the difference was significant at p = 0.05. The nitrifying bacteria (NB) associated with the impacted soil were the most adversely affected. There was 2.11 to 139 times higher concentration of the different heavy metals in the impacted soil than the control and 1.13 to 1.26 x 104 times higher Total petroleum hydrocarbon in the impacted soils in both seasons and these differences were significant (p = 0.05). Dehydrogenase activity was 2.8 to 3.1 times higher in the control soils compared to the impacted soil whereas Phenol oxidase was 15.14 to 15.75 times higher in the impacted soils in both seasons. This study indicates that Exploration and Production activitiesi in the coastal wetlands if not carried out according to specified guidelines by the environmental control agencies can result in the reduction of beneficial soil bacterial population and diversity, high concentrations of heavy metals, petroleum hydrocarbon and decreased dehydrogenase activity at impacted explored wetland site. It also revealed non-impacted regions of this explored wetlands not within oil pipe-line routes are fit for agricultural use.