Effects of Heavy Metals on Benthic Invertebrate Abundance in Owena River

Abstract

Heavy metals are pollutants of ecological concern in the aquatic ecosystem. Macrofauna plays significant roles as bio-indicators in the aquatic ecosystems as well as in food sources for fish. This study examined the presence of heavy metal contaminants in Owena river and if the presence affects the abundance and diversity of benthic invertebrates from the river. The results showed two classes of phylum Mollusca, class Gastropoda (three) and Bivalvia (five) which are dominating class of macrozoobenthos. The Shannon diversity index of Owena River (H) was 1.38 while the Evenness (E) showed 0.66. The concentrations of heavy metals investigated in the river were within World Health Organization’s (WHO) limits. However, in the sediments the concentrations of Fe (19.37±0.355-26.00±0.006 mg/l), Cd (0.13±0.000-0.20±0.00 mg/l), Zn (1.13±0.006-1.35±0.006 mg/l and Cr (0.26±0.017- 0.35±0.003 mg/l) were seen to be higher than the permissible limits of WHO. The order of pollution in the surface water was as follows Fe > As > Cd > Zn>Pb > Cr while that of the sediments was Fe>Zn> Cr > Cd > As>Pb. Positive correlation was found between Margaritifera magaritigera and Pb, while Lymnaea stagnalis showed significantly positive correlation with Zn, Cd and As. The occurrence and absence of some benthic macroinvertebrates in Owena River suggests the effect of pollution from anthropogenic activities. Therefore, a good management program is necessary so as to conserve the significant biota present in the river and prevent pollution for domestic purposes.