Pages: 1-12

Abstract

The Upper Reaches of Orashi River in Onelga Local Government Area of Rivers State, Nigeria accommodates different human activities such as dredging, fishing, bathing, washing, laundry to mention but a few. The study determined species composition, diversity, abundance and distribution of phytoplankton assemblages of the Upper Reaches of Orashi River. Also, it investigated the spatial and temporal variations of the phytoplankton of the Upper Reaches of Orashi River. Phytoplankton samples were collected monthly between April and June 2016 from three (3) sampling stations established along the River course according to standard method. The samples were identified microscopically. Data analyses were done using Statistical Package for Social Sciences (SPSS) for two-way analysis of variance at 0.05 level of significance and descriptive statistics. A total of 798 cell counts from 3 families (Bacillariophyceae, Chlorophyceae and Cyanophyceae) and 24 species dominated by diatoms (Bacillariophyta) were recorded. The species diversity indices (Margalef and Shannon) were identified. There were no significant spatial variation between Bacilliariophyta, Chlorophyta and Cyanophyta (p<0.05). Dominant species of phytoplankton were Gyrosigma sp (74 cell counts), Meridion circulare (71 cell counts) and Melosira varians (63 cell counts). The presence of dominant Bacillariophyceae indicates that this River is perturbed and organically polluted. Also, the recorded Melosira varians (Bacillariophyceae), Oscillatoria limosa and O. lacustris (Cyanophyceae) denotes nutrient enrichment of this River. Anthropogenic activities within and around this River should be controlled. Also, regular monitoring and evaluation of the study area is advocated.