Impact of Chronic Crude Oil Pollution on Nitrification in Edaphic Systems

Nitrification plays a key role in regulating soil fertility, concentration of soil inorganic nitrogen and production of the greenhouse gas, nitrous oxide, from soil. This study investigated the effect of long-term crude oil pollution on the activity and abundance of autotrophic nitrifying bacteria in impacted soils from Bomu and Abonema in the Nigerian Niger Delta compared to unpolluted ecosystems. Nitrifier activity was investigated by determining the soil oxidation potentials while the most probable number microtechnique using Winogradsky media was used to ascertain nitrifying bacteria abundance. The results highlighted the dominance of Nitrosomonas and Nitrobacter in both polluted and unpolluted soils. Nitrifier activity was found to be higher in the polluted soils than in the unpolluted soils while quantification of the nitrifying bacteria revealed that polluted samples had higher nitrifier counts. Statistically significant differences existed between nitrifier counts and activity (p≤0.05) between polluted and unpolluted systems with positive correlation between nitrifying bacteria counts and oxidation potential. The ammonia oxidising bacteria proved to be more sensitive to chronic crude oil pollution than the nitrite oxidising bacteria. Following long-term crude oil exposure, approximately twice the number of nitrifying bacteria had 3 – 5 times the level of activity observed in the unpolluted systems.