6. Benthic Macro-Invertebrates as Indicators of Water Quality in Ogunpa River, South-Western Nigeria

Abstract

This study assessed the water quality of Ogunpa River using benthic macro-invertebrates. Three sampling stations were purposively selected and replicated trice. Benthic samples were collected fortnightly using Van Veen 0.5 m bottom grab for a period of twelve months (January – December, 2018). Water samples were collected from the stations and determined using standard methods. The mean water parameters recorded were; Temperature (26 ^oC ± 0.12), Dissolved Oxygen (5.05 mg/L ± 0.47), Chemical Oxygen Demand (29.53 mg/L ± 0.51), Nitrate (4.40 mg/L ± 0.20) and pH (7.82 ± 0.18). Temperature and pH were not significantly different (P>0.05), COD and nitrate were significantly different (P<0.05) while DO for stations A and B were significantly different (P<0.05) from station C. Seven (7) benthic macro-invertebrates namely Lymnaea truncatula, Lymnaea glabra, Chironomus sp., Gyrius sp., Anisoptera, Hirudo sp. and Tubifex sp. belonging to five (5) families were recorded. Overall, a total of 9,989 macro-invertebrates were recorded from all the stations with the highest relative abundance in station C (35.3%). Family Lymnaeidae had the highest abundance (53.1%) while the lowest was Odonata (6.9 %). The abundance of pollution tolerant benthic macro-invertebrate L. truncatula (36.5%) indicated that the river is under pollution stress. There is an urgent need for proper management measures to be put in place in order to maintain good water quality for the sustenance of aquatic life and meeting the United Nations Sustainable Development Goal 6 (clean water and sanitation).