The heavy metals and benthic macroinvertebrates diversity and abundance of Oyun River sediments, Ilorin, Kwara State, Nigeria

Abstract

Anthropogenic activities in and around water bodies disrupt their physico-chemical and biological conditions such as sediment qualities and diversity of benthic macroinvertebrates. The purpose of this study was to assess the pH and heavy metal (Mn, Zn, Fe, Cu, Pb, Ni, Cr, Co and Al) contents of the sediments and the occurrence of benthic macroinvertebrates of Oyun river, Ilorin East local government area, Ilorin, Kwara state, Nigeria. Three sampling locations (upstream, midstream and downstream), 500 m apart were selected along the river based on the flow of water current. The kick method (using sweep net) was used to collect sediments and benthos once every two weeks from February to May, 2016. One-way ANOVA was used to assess the variations among the values and the sampling stations, and the macroinvertebrates were identified using standard identification guidelines. The pH of the sediments was alkalinic with mean values 8.39±0.30, 8.14±0.34 and 7.95±0.57 at the upstream, midstream and downstream respectively. All the heavy metals exceeded threshold limits and highest at the downstream. A total of 5 macroinvertebrate species belonging to 2 classes (Insecta 68.97% and Gastropoda 31.03%) were identified. The most abundant species was Chironomus plomusus while the least abundant was Laccophilus congener accounting for 36 (41.38%) and 1 (1.15%) respectively. The low abundance of benthic macroinvertebrate species coupled with the non-occurrence of EPT indexed taxa and the higher abundance of the pollution-tolerant taxa (Chironomus plomusus) could reflect the level of pollution stress of this Oyun River system. Therefore, strict pollution management of this river is recommended.