Nutritional richness of sediments from crude oil impacted Iko River Estuary, Eastern Obolo L.G.A, Nigeria

Abstract

This was a longitudinal study that lasted twelve calendar months;and conducted in three selected stations along the course of a crude oil impacted Iko river estuary, Eastern Obolo LGA, Akwa Ibom State, Nigeria.Standard protocols were followed in collection and analysis of sediment samples. There were spatio-temporal variations in total hydrocarbon content (THC): lowest value (101.40 mgkg^-1) recorded at Station 2 in October while the highest value (219.60 mgkg^-1) was obtained atStation 1 in April; dry season mean value of 162.31 ± 22.67 mgkg^-1 was significantly (p<0.05) higher than that of wet season (137.19 ± 34.59 mgkg^-1). The levels of Total Nitrogen (TN) in the study area were quite low, with values that ranged from 0.19 - 0.50 %, 0.20 - 0.44 % and 0.15 - 0.046 % in Station 1, 2 and 3 respectively with no significant differences observedirrespective of seasons. Levels of Ammonium ions (NH4+) recorded in the sediments were 2.28 - 5.11 mgkg^-1, 2.96 - 6.01 mgkg^-1and 2.41 - 5.72 mgkg^-1 in Station 1, 2 and 3 respectively. Nitrate (NO₃-) lowest value of 11.60 mgkg^-1 was recorded in Station 2 while the highest value of 36.00 mgkg^-1 was recorded in Station 3. Wet season NO₃- mean value was higher (27.51 ± 4.62 mgkg^-1) than that of the dry season (18.38 ± 4.06 mgkg^-1). Phosphate levels in sediments were not significantly different among stations and seasons. The mean concentrations of Sulphate in sampling stations were 48.53 ± 4.62 mgkg^-1, 36.96 ± 6.93 mgkg^-1 and 42.25 ± 5.98 mgkg^-1 for Stations 1, 2 and 3 respectively. There was no remarkable spatial variation in the Chloride levels of the sediments. Nevertheless, influence of season was significant (p< 0.05) as dry season mean value of 173.16 ± 12.53 mgkg^-1 exceeded that of wet season (131.78 ± 20.76 mgkg^-1). Both negative and positive associations  between pollutants and nutritive salt levels in the sediments were recorded across sampling stations irrespective of the season. From the results, it can be concluded that higher level of nutritive salts were in the sediments at seasons where hydrocarbon contamination of the sediment was lowest.