Post‐Impact Assessment of Oil Pollution in Agbada West Plain of Niger Delta, Nigeria: Field Reconnaissance and Total Extractable Hydrocarbon Content

Abstract

Typical post-impact assessment of an oil-spill-impacted site in Agbada west plain of the Niger Delta basin of Nigeria was carried out 13 months after recorded incidence of spillage, using empirical indices of reconnaissance and extractable hydrocarbon content. Field-reconnaissance surveys revealed lower species' numbers and diversity of surface and subterranean flora and fauna. The presence and absence of such plant species as Elaeis guineensis, Musanga cecropiodes, and Andropogon gayanus, as well as animal species like earthworms and nematodes in sampled plots, corroborated the evidence provided by the total extractable hydrocarbon content (of (2.53+/-0.43)x10(2) mg/kg and (2.00+/-0.76)x10(2) mg/kg at surface and subsurface depths, resp.) on the level of degradation and/or regeneration at the polluted site. The most important evidence that oiling must have been responsible, at least in part, for the reduction in species' number and diversity was provided by the plant cover, Andropogan gayanus, which occurred at a lower density of 0.9 plants/m2 in the oil-impacted plots and 14.00 plants/m2 in the unimpacted reference plots of an adjacent, geographically similar area. The presence of this species on site thus presented a significant difference (P<0.05) of over 85%, and indicated exhaustion or impoverishment of impacted soils. Elaeis guineensis, with a population density of 0.1 stands/m2, provided evidence of past cultivation on site, while species like Musanga cecropioides, with a density of 0.5 stands/m2, at the unimpacted site, confirmed the abandonment of the farmstead over a long period of time. For the fauna, the most sensitive indicator of hydrocarbon toxicity was provided by nematode Xiphinema sp. that were completely absent in the oil-impacted site.

Hydrocarbon contamination of a typical mangrove floor in Niger Delta, Nigeria

“…The presence of oil on the mangrove floor, for instance, will encumber the decay process of the litters from mangroves, which ordinarily enhance the accumulation of organic matter. Osuji et al, (2004) and many past studies on the Niger Delta have reported such higher than normal hydrocarbon concentrations in soils many months after oil spillage and have noted similar deteriorations of the mangrove system as a result of such spillages. Aside from the said fertility problems that are usually associated with contamination of the mangrove floor by spilled-oil, oiling of the mangrove system may also be accompanied with many other features such as leaf loss or complete defoliation of the flora from either root or leaf exposure to the oil especially in severely impacted areas; this includes the defoliation of the characteristic Rhizophora mangrove seedlings in affected areas (Ekweozor, 1998).…”

“…This perhaps explains the defoliated state of some mangroves found at the study site (cf: Figs 2 and 3), especially those that were within the immediate vicinity of the right-of-way. High hydrocarbon content of soils has been known to affect soil physico-chemical properties, which in turn affect the agricultural potentials of such soils (Amadi and Dickson, 1993;Ezebuiro, 2004 andOsuji et al, 2004). Although soils of the mangrove floor under consideration may well be of limited cultivation value on account of the people's dual occupation in fishing and farming, the presence of such levels or range of hydrocarbons at the study site might severe agricultural productivity.…”

“…Shriveling, cuppingup of leaves, arrested expansion of buds and some degree of foliar necrosis have also been identified as marked stress signs of a mangrove system plagued with petroleum hydrocarbons (Odu et al, 1985). In a recent field reconnaissance survey, an abysmal decimation of juvenile red mangrove by oil spillage was observed along the Nembe axis of Niger Delta, resulting from either short or long time exposure of the flora to toxic effects of the petroleum hydrocarbons (Obute, 2004). Other species of the mangrove system in the study area that could be adversely affected in the same vein include Paullina pinnata, Antidesma spp, and Ouratea spp, known to have over 50% frequency of occurrence in this area (cf: Table 1).…”

“…Studies have shown that just as the nature of the hydrocarbon fluid produced is peculiar to its environment of recovery, so also is its impact specific on any affected site (Indonesia No. 41, 1999;Osuji et al, 2004 andOsuji andOnojake, 2004). For instance, in an environment that is completely terrestrial, the penetration and spread of oil in the soil will depend on the nature and topography of the soil environment.…”

The nexus of oil, conflict, and climate change vulnerability of pastoral communities in northwest Kenya

“…Particularly in Nigeria, the detrimental effects of oil exploitation on the environment and the communities are well studied (for example, Aghalino, 2009;Anifowose et al, 2012;Ikelegbe, 2001;Obioha, 2009;Osuji et al, 2004). Given the significant revenues earned with oil and the persistent high levels of insecurity and urban poverty, oil has mostly become a "resource curse" for communities in rural Nigeria (Sala-i-Martin and Subramanian, 2013;Obi, 2012;Idemudia, 2012).…”