Soil Microarthropods in a Secondary Rainforest, Rivers State, Nigeria - IV- The Impact of Oil Pollution on Their Vertical Distribution

Studies were undertaken, May, 2007-April, 2009, to document species richness, bioindicator species, abun- dance, density, vertical distribution, etc. of soil microarthropods (mites, collembolans) in unpolluted and polluted habitats in a secondary rainforest, Rivers State, Nigeria. This paper focuses on the effects of oil pollution on the vertical distribution of these mesofauna. Sampling was effected monthly by a bucket-type auger to a depth of 15.0cm in four habitat-types (un- polluted, polluted by oil spills approximately 1yr, 3yrs and 6yrs pre-study). The modified Bukard model of the Ber- lese-Tullgren funnel was used for extraction. Identifications were undertaken using standard keys and unidentified speci- mens were compared to type specimens. In the unpolluted and polluted (3 and 6yrs pre-study) habitats, there was an inverse relationship between mite/ collembolan abundance/density (except in the Prostigmata) and soil depth; however, the correla- tions were not significant. In contrast, there was a significant direct correlation between mite abundance/density and depth in the habitat, polluted 1yr pre-study (F=29.11; df=1.3; p 0.05). In the unpolluted habitat, approximately 90% of all collembolans were found above a depth of 10.0cm; this declined to 30% in the habitat, polluted 1yr pre-study, and rose to 50% and 85% in the habitats, polluted 3 and 6yrs pre-study.