Physical, chemical and periphyton/phytoplankton study of Onah Lake, Asaba, Nigeria

The physico-chemical parameters and periphyton composition of Onah Lake was monitored. The data obtained revealed that the concentration of all the nutrients were higher during the dry season than the rainy season. The observation connotes a discernible seasonal pattern in the concentration of the various nutrients in the lake. With the exception of transparency, total alkalinity and conductivity, that were significantly different (P parameters were not significantly different (p>0.05) in the stations. Transparency was significantly lower in the upstream station as opposed to the down stream station that recorded a higher value. The condition favoring the abundance of nutrients was discussed. The principal component analyzer generated a sequence of variates known as components in a correlation matrics. Three components were selected which account for 100% of variance in the physico-chemical parameter, viz: ionic conductivity factor contributed 26.07%, nutrient factor contributed 40.61% while dissolved oxygen factor contributed 33.32%. Three divisions, eight families and ten species of periphyton were encountered. The most abundant periphyton species recorded are Closterium spp. (26.37%) Cosmarium spp. (18.63%) and Ulothrix spp. (16.56%). The least encountered species was Anabaena spp. (2.88%). This was not implicated in any toxic bloom.