Impacts of Effluents on the Limnology of a Tropical River, Southwestern Nigeria

The physico-chemical parameters, composition and abundance of macrobenthic invertebrates were studied in River Ogbere, from November 2009 to May 2010. Water samples and macrobenthic invertebrates were collected from three selected sampling sites and analysed using standard methods. The mean biochemical oxygen demand (106.9 ± 58.25 mg/l), Nitrate (40 ± 30.8 mg/l), dissolved oxygen (4.2 ± 2.16 mg/l) and total suspended solids (124.02 ± 16.09 mg/l) were not within permissible standard limits suitable for aquatic life and domestic purposes. Higher concentration of metals was recorded in sediments than surface water. A total number of 563 individuals of macrobenthic invertebrates belonging to 27 genera and four phyla were recorded. The dominant invertebrate in River Ogbere during sampling period was Chironomus sp (65.01%). Other pollution tolerant species encountered were leeches (Pisciola, 0.36%) and earthworm (Eiseniella, 1.95%). The River Ogbere could be regarded as polluted since the adverse water quality has led to presence of mainly pollution tolerant taxa of macrobenthic invertebrates in the waterbed.