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

摘要

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 (0.01), whereas seasonal variation of these variables was not statistically significant (p>0.05). Significant seasonal variation (0.05) was, however, observed in temperature, Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD), Total Dissolved Solids (TDS), 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-Weiners diversity index (H1) of 0.23 and Simpsons dominance index (D) of 0.017. A highly significant variation (0.01) was observed in spatial distribution and seasonal abundance of most of the algal groups, whereas taxa occurrence showed no significant difference (p>0.05) among the stations and the seasons. A total of 8 taxa of zooplankton belonging to 4 genera were identified. Rotifera were the most prevalent group with 4 taxa followed by Cladocera with 2 taxa while, protozoa and copepoda recorded 1 species each. A highly significant spatial and seasonal variation (0.01) was observed in zooplankton abundance among the stations. The zooplankton dominance profile also showed rotifers ranking the highest with Shanon-Weiners Diversity index (H1) of 0.21 and Simpsons Dominance Index (D) of 0.014. Correlation coefficient also showed a highly significant relationship (r = 0.881; 0.01) between zooplankton and phytoplankton abundance. Also, a highly significant relationship (r = 0.961; 0.05) existed between overall plankton distribution and abundance and water quality parameters. Alternative sources of building materials such as Fly Ash and Industrial Hemp have been recommended in order to reduce or eliminate the need for sand for building purposes.