Assessment of the Ecological Status of OPA Reservoir, ILE IFE, Nigeria Based on a Comparative Study of its Planktonic Community and Water Quality Parameters

Study to determine the ecological status of Opa reservoir, Ile Ife Nigeria was conducted based on the plankton's diversity and physicochemical characteristics of the reservoir. Water samples for the analyses were collected from three established investigated stations on the reservoir for a period of one year between November 2012 and October 2013. Most of the physicochemical parameters' result were within recommended limits of the NESREA for aquatic life, but some heavy metals (Ni and Cr) were above permissible limits. One hundred and thirty-six (136) plankton species belonging to thirteen taxa were encountered whose total abundance and distribution were influenced greatly by dissolved oxygen, salinity and light obstruction parameters. Notable, recorded species at the riverine (Cryptomonas ovata, Branchionus angularis and Cyclops) revealed the unacceptable quality of the reservoir’s influx. Besides, the observed low species diversity index, at all zones of the reservoir investigated, revealed dominance by few species that characterized eutrophicated waters. Furthermore, the presence of plankton pollution tolerant species (Anabaena sp., Navicula sp. and Peridinium sp.) also suggested a minimal level of organic pollution in the reservoir. The water qualities of Opa reservoir at the Lacustrine zone (76.14) and Transition zone (67.89) were of occasional threatened while Riverine zone (63.57) was frequently impaired according to the CCME Water Quality Index.