BENTHIC MACROINVERTEBRATE IN RELATION TO POLLUTION TOLERANCE INDEX OF A CREEK FLOWING THROUGH AN URBAN AREA IN SOUTHERN NIGERIA
Assessment of the pollution tolerance index (PTI) of Ekpan creek Delta state, Southern Nigeria was studied fortnightly from January to June, 2007. Macrobenthic invertebrates were collected from floating macrophytes (Eichhornia crassipes) using the quadrant sampling method and dusted in formalin solution. Physico-chemical parameters were analyzed using test methods according to APHA, 1998 while heavy metals were analyzed with an atomic absorption spectrometer (PYE unicam SP2900) after digestion. Eleven (11) major groups were recorded comprising of 45 species that were sorted, identified and counted. Station one had a relative abundance of 41.1%, station two had 30.7% and station three had 28.2 % respectively of the total population. The dominant groups were Gastropoda (69.9%) and Crustacea (22.0%) while others were rare groups. Polychaete, Crustacea, Coleoptera, Odonata, Gastropoda, Arachnida, occurred both in the rainy and dry season with the exceptions of Collembola and Ephemeroptera which occurred only in the rainy season. Diversity of the benthos showed no significant variation between the stations. There also existed a significant correlation (p>0.05) between most of the groups. The PTI values ranged between 11-14 in the study stations and were less than 10 in most months indicating a compromised water quality.