In order to assess the environmental impact of site activities and ecosystem change brought about by stress, basic baseline data are necessary to characterize the normal environment so that environmental quality control programmes can be developed with a firm ecological base.

The programme and methodology adopted in our field surveys to assess the character, magnitude and extent of pollutant effects on soil, vegetation and water, as a basis for economic assessment of pollutant effects on agriculture, forestry and the aquatic system and for preparing environmental impact statements, are presented.

These techniques were modified and adopted in the environmental impact study of the Isampou Manifold Oil Spill, a study which circumstances made necessary seven years after the oil spill. Reliance on the extent of pollution soon after the incidence was based on the determination of total hydrocarbons at creek bottoms as well as on the determinations of nickel/vanadium ratios.

Hydrocarbon contents of creek banks and creek bottoms were within biogenic levels at the time of field sampling. Ni/V ratios were high in heavy impact areas and decreased in areas of medium and very light impact areas. Use of the Ni/V ratio as evidence of past oil pollution agreed closely with a sketch of the extent of crude oil pollution drawn by the Shell Petroleum Development Company seven years earlier.

There were no abnormal vegetation features. The presence of 10-15 years old Musanga cecropioides at the edge of the manifold slot and creeks indicated that vegetation above water level was not affected by the oil spillage.

The physico-chemical properties of the waters, plankton composition and density of the species found, as well as the presence of endoproct bryozoan in the benthos showed that the aquatic system had by the time of sample collection, completely recovered from the oil spillage.

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