Composition of Cyanobacteria in Relation to Physico-Chemical Characteristics of Four Rivers in the Niger Delta

Abstract

The composition of Cyanobacteria and physico-chemical charactaristics of Sombreiro, Orashi, New Calabar, and Bonny Rivers in the Niger Delta was studied for one year (September, 2012 - August 2013). Cyanobacteria were enumerated using the Lugol’s solution method. The samples were centrifuged at 360 rpm for 15 minutes, the supernatant was carefully removed and the pellets re-suspended in 0.5 ml distilled water. The concentrated sample was placed in a haemocytometer and examined under the microscope at a magnification of 400×. The Cyanobacteria were identified and total number of species recorded using keys and checklists. Twelve species of cyanobacteria recorded in the study include Anabaena sp (42.34%), Microcystis sp (25.26%), Cylindrospermopsis sp (22.60%), Nostoc sp (2.08%), Synechococcus sp (1.44%), Aphanizomenon sp (1.44%), Lyngbya sp (1.17%), Oscillatoria sp (1.08%), Nodularia sp (1.08%), Chroococcus sp (0.81%), Trichodesmium sp (0.36%) and Schizothrix sp (0.36%).  The most predominant species in this study was Anabaena sp (42.34%) in both the fresh and brackish water systems. The Shannon – Wiener diversity index in the four rivers ranged from 0.67 – 1.26. The population of cyanobacteria enumerated ranged from 2.0 × 10³ to 1.1 × 10⁵. The maximum value for cyanobacteria population falls within caution level and Alert 2 level of WHO (2003) which is a safe level. New Calabar River had the highest relative abundance of Microcystis sp, Anabaena sp, Cylindrspermopsis sp, Lyngbya sp, Chroococcus sp and Synechococcus sp. Correlation coefficients of cyanobacterial population and physico-chemical parameters were positive with Biochemical Oxygen demand (BOD), Chemical Oxygen Demand (COD) in Sombreiro River. Cyanobacterial counts also correlated positively with alkalinity in Orashi River and New Calabar River. The results indicate that higher organic load and more alkaline pH encourage cyanobacterial diversity.

Keywords: Cyanobacteria, Composition, Rivers, Nigeria