Seasonal Influence on the Microbiology and Physicochemistry of Crude Oil Polluted Wetlands

Abstract

Pollutants such as crude oil spills in an environment, affect the physical, chemical and biological properties of that environment. This study was conducted to determine the effect of seasonal variations on the microbiological and physicochemical characteristics of three crude oil-polluted wetlands in Rivers State, Nigeria. Soil samples were collected at 3 depths (0-15cm, 15-30cm and 30-45cm) with the aid of a hand auger, sampling was done for a period of twelve months covering the rainy (March to August) and dry seasons (September to February). Samples were analyzed for physicochemical characteristics, using standard analytical and microbiological methods. The data obtained was analyzed using the statistical package for social science (SPSS) version 22 and Duncan’s multiple range test was used to separate means where differences occurred. Microbiological analyses showed that significantly higher microbial counts were observed in the dry season than in the rainy season in the wetland samples which could be due to favourable environmental conditions during the period of study. Wetland soil total heterotrophic bacterial (THB) count in the wet season ranged from 1.09x107cfu/g to 10.45x107cfu/g and from 2.43x107cfu/g to 18.56x107cfu/g in the dry season. Total heterotrophic bacteria had the highest population in all soil depths (0-15cm, 15-30cm and 30-45cm) in both seasons. Hydrocarbon-utilizing bacteria such as Bacillus subtilllis, B. rigui, B. flexus, Lysinibacillus macrolides, Staphylococcus aureus, Proteus penneri and fungi such as Aspergillus species, Fusarium species, Mucor species and Rhizopus species were genetically identified in this study. Temperature and other physicochemical parameters in the wetlands were altered due to the variation in season. Higher temperature ranges were observed in the dry season than in the rainy season as seen in Iwofe, temperature ranged from 26.500C (0-15cm) to 28.500C (30-45cm) in the rainy season while in the dry season it ranged from 31.500C (0-15cm) to 33.500C (30-45cm) which was above FEPA permissible limit of 300C for soil temperature. The study showed that season of study as well as crude oil spillage have significant effects on the microbiology and physicochemical characteristics of wetlands and therefore, contribute to microbiological degradation in wetlands.