Effects of abattoir effluent on composition and distribution of insect fauna in Lower Ogun River, South West Nigeria

Abstract

The ecological impacts of abattoir effluents discharge into Lower Ogun River were assessed by studying the composition, distributions and diversity of insect fauna of the river both in lsheri-Olofin(abattoir effluents discharge/downstream) and lshasi (upstream/control) areas for 24months (January 2006 to December 2007). The prevalence of organic pollution was evident in the downstream area with high levels of Biological Oxygen Demand (BOD), Dissolved Carbondioxide (DCO₂) and Ammonia (NH₃) but lower transparency, Dissolved Oxygen (DO) and Electrical Conductivity. Upstream area had a total of 281 insects cutting across 35 taxa of eight orders, while a total of 449 insects of eight taxa cutting across three orders were encountered downstream. Pollution sensitive insect taxa (Odonates, Trichopterans, Plecopterans and Ephemenopterans) were found only in the upstream area, while downstream area had the opportunistic/pollution tolerant ones; Chironomus (52.56%) and Eristalis (41.43%) as the dominant insect taxa. Higher Margalef diversity and Evenness of distribution but lower Simpson dominance indices were recorded upstream than downstream. The ecological significance of the effect of abattoir effluents on the insect fauna of Lower Ogun River was discussed.

Key Words: Organic pollution, Insect fauna, Distribution, Diversity, lower Ogun river