TITLE:
Ammonium Oxidizing Bacteria Activity and Nitrification Rate in Oil Contaminated Wetland Soil under Remediation with Nutrient Supplements and Leguminous Plants
AUTHORS:
Richard C. John, Emem S. Ntino, Joseph P. Essien
KEYWORDS:
Wetland Soil, AOB, Contamination, Nitrification, Crude Oil, Ammonium
JOURNAL NAME:
Journal of Environmental Protection,
Vol.7 No.4,
March
30,
2016
ABSTRACT: Previous investigation on the impact of
crude oil on the growth of tropical legumes and its effect on nitrogen dynamics
in wetland ultisol showed that oil contamination reduced N uptake by plants but
increased N accumulation in soil microbial biomass. Moreover, the presence of
hydrocarbons widened the C/N ratio in soil and led to more available N being
immobilized by soil microorganisms. The present study was carried out to
evaluate the activity of ammonium oxidizing bacteria (AOB) and their
nitrification potential rate (NPR) in wetland soil under a remediation course.
Mineralization studies showed that ammonium-N levels decreased while nitrate-N
increased progressively in the uncontaminated soil (control) cultivated with
leguminous plants (cover crops) during the 12 weeks remediation period.
However, the remediated soils were affected in different ways. The experimented
soil cultivated with Centrosema pubescens had higher mineral
nitrogen (NH4-N, NO3-N,
NO2-N, Total N and P) than soil cultivated with
Calopogonium mucunoides and Pueraria
phaseoloides. AOB counts recorded were in the ranged, 2.25 ×
102 - 2.66 × 105, 2.31 × 102
- 2.11 × 104 and 4.25 × 102 -
2.98 × 104 respectively. The highest NPR was found in uncontaminated soil
(11.68 - 60.92 nmol N/g dry weight soil (DWS)) followed by soil treated with poultry
manure (9.65 - 24.86 nmol N/g DWS/h), NPK (7.88 - 39.45 nmol N/g DWS/h) and in
the oil-contaminated soil (0.11 - 1.87 nmol N/g DWS/h). The relations between
NH4-N concentration and NPR in soil cultivated with
Centrosema (r = 0.852), Calopogonium (r =
0.745) and Pueraria (r = 0.722) were positively significant
at 95% confidence limit. Similarly the relations between AOB density and NPR
for Centrosema (r = 0.654; P = 0.05),
Calopogonium (r = 0.588; P = 0.05) and Pueraria
(r = 0.518; P = 0.05) were significant. The findings imply that nitrification
potential of crude oil- contaminated soil differs significantly with the
nutrient amendment/treatment technique adopted for remediation. Our research
has shown that treatment of uncontaminated soil with cover crops increased AOB
and nitrification rate. More so, contaminated soil treated with poultry manure
and NPK-fertilizer, cultivated with covers crops resulted in remarkable
reduction in hydrocarbons content and increased population of nitrifiers and nitrification
potential rates of wetland soil over time. However, contaminated soil treated
with poultry manure and cultivated with Centrosema pubescens
is more effective in bioremediation of crude oil-contaminated soil.