First record of bloom-forming cyanobacteria, Microcystis aeruginosa Kütz. and M. wesenbergii. Komárek (cyanophyta) incidence in Oyan Dam, Ogun State, South-West Nigeria
This investigation revealed the incidence of floating scum mint green colouration of bloom-forming bluegreen algae, Microcystis aeruginosa Kütz. and M. wesenbergii Komárek in November 2015 at Oyan dam. Water bodies were observed to have mint green appearance. During this observation, all gates and valves were reported to have been closed for a whole month (October-November 2015) and water level at the forebay area was 58.98 m depth. Higher dissolved oxygen (>5.10mg/L), biological oxygen demand (>10mg/L) and chloride ions (>12.0 mg/L) values were recorded while low transparency (≤1.26 m) value was observed. Depth of the water ranged between 10.80 m and16.70 m. This probably explains why Microcystis spp. take the advantage of water residence time to proliferate couple with the alkaline status of the water pH 9.3 probably from the seepage from the sand mining activities around the area. For effective alternatives to prevent further occurrence, water residence time should be reduced, flushing should be enhanced by opening of the valves and artificial mixing should be encouraged. The results of this study show the existence of toxic cyanobacteria in Oyan dam and the need for continued study to prevent water borne diseases.
Keywords: Cyanophyta, Microcystis, dam, water chemistry, algal bloom