Plankton Communities of Ikpa River, South East Nigeria Exposed to Sand-Dredging Activities

The plankton communities of Ikpa River downstream from a sand-dredging area were studied for a period of 12 months (March 2010 to February 2011), covering dry and wet seasons. Most physico-chemical parameters (pH, turbidity, silicates, transparency and conductivity) exhibited highly significant spatial variation, whereas seasonal variation of these variables was not statistically significant. Significant seasonal variation was, however, observed in temperature, Dissolved Oxygen, Biochemical Oxygen Demand, Total Dissolved Solids, Phosphorus, Nitrates and Conductivity. A total of 51 taxa of phytoplankton, belonging to 43 genera and 5 families, were identified during the period of study. Bacillariophyceae recorded the highest relative abundance with 52.41% followed by Chlorophyceae with 32.05%, Cyanobacteria with 13.35% while Euglenophyceae and Dinophyceae contributed 1.26% and 0.83%, respectively. Among the diatoms, Melosira granulata was the most dominant species with Shanon-Weiner's diversity index of 0.23 and Simpson's dominance index of 0.017.