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.
