The Niger Delta ecosystems of Nigeria, typically consisting of mangrove swamps and riparian forests, have come under threat in the last six decades as a result of environmental pollution from oil exploration, drilling, refining and transportation. This study examines two Niger Delta streams (Ogba Evie and Otor) to ascertain the extent of hydrocarbon and heavy metal pollution and the status of the biotic communities in them. The physicochemical parameters of surface water samples indicate that dissolved oxygen is significantly lower in Ogba Evie stream which had some of its surface covered with oil films compared to Otor stream. Oil and grease levels were, however, well within the National Environmental Standards and Regulation Enforcement Agency (NESREA) safety limits. Both streams had high concentrations of polycyclic aromatic hydrocarbons (PAHs) and several heavy metals. Overall, the diversity indices point to low phytoplankton and zooplankton species diversity and abundance. Phacus curvicauda Swirenko was the most abundant phytoplankton in the Ogba Evie stream, while Synedra ulna (Nitzsch) Ehrenberg was predominant at the Otor stream. The copepod, Cyclops strenuus Fisher was the most abundant zooplankton common to all sections of both streams. Although, no significant relationship was observed between PAH and plankton abundance, the trend observed in both streams may be a reflection of their present-day pollution rates.
Key words: Oil spill, biotic indices, water quality, hydrocarbon pollution, biomonitoring.
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