BIO-INDICATOR POTENTIAL OF ODONATA IN ASSESSMENT OF WATER QUALITY IN BENIN-OWENA RIVER BASIN CATCHMENT, IGBARA-OKE, ONDO STATE, NIGERIA.

Abstract

Odonates are abundant and important members of aquatic fauna of a variety of freshwater ecosystems. Ecologically, dragonflies and damselflies are good indicator of the condition of terrestrial as well as aquatic ecosystems. Heavy metal concentration of aquatic habitats has increased due to dense anthropogenic activity in recent years. Because of this condition, aquatic organisms are exposed to elevated levels of metals which threatens the health of aquatic organisms as well as human. The research was carried out between June 2017 to July 2018, comprising of 4 months of dry season and 8 months of wet season. All Samples were collected once in a month, between the hours of 9am -2pm. Penultimate and Ultimate Odonata nymphs were collected for rearing using kick net, adult were also collected with sweep net. Some parameters were measured at the sites, they include: dissolved oxygen (mg/L), water temperature (°C), Conductivity(μS/cm), pH, Total dissolved solid(mg/L) and Turbidity(NTU) were determined with the aid of HANNA multipara meters Water samples collected were acidified with 2ml HNO 3 and analyzed for heavy metals using AAS 210 VGP Buck Scientific. Analysis of a mixture of metal standards (As, Cr, Cu, Pb, Zn, and Ba). Chromium and Arsenic were the priority metal that exceeded set limits by WHO, but their high values was limited to seasonal variations. The Shannon-wiener diversity index values obtained at the three sites are: (Owena dam H` = 3.057, Elemo stream H`= 2.876, and River Aro H`= 2.276). This study has provided data on the diversity of Odonata inhabiting the three water bodies in Benin- Owena River Basin catchment Igbara-Oke. The DO in Elemo stream was significantly impacted by the palm oil mill activity around the water body, however, this did not impact on the rich species diversity of the water. This result reveal that assumption cannot be make on the quality of water using only the diversity index of Odonata but with the combination of other parameter.