Phytoplankton as Bioindicators of Water Quality in Saminaka Reservoir, Northern-Nigeria

A small reservoir constructed in 1975 for domestic and agricultural water supply was studied for 12 months which covered six months of wet season (May to October 2008) and dry season November 2008 to April 2009). Phytoplankton and water samples were collected and analysed using standard methods at three sampling stations. Number of Phytoplankton species and class abundance showed the order Bacillariophyceae > Cholorophyceae > Cyanophyceae > Euglenophyceae. The physico-chemical characteristics (Nitrate-Nitrogen, Phosphate-phosphorus, Total Hardness, Total Alkalinity, Electrical Conductivity, Dissolved Oxygen, biochemical Oxygen Demand and Seechi disc Transparency) of the water in the reservoirs showed significant relationship with phytoplankton abundance. Shannon-Weiner diversity index showed that species diversity was higher in the dry season than the wet season, the number of individuals was also higher in the dry season. The presence of organic pollution indicators Euglena gracillis and Oscillatoria sp and a bloom of cyanotoxin producing Microcystis aeruginosa is a warning sign of the deteriorating condition of the water quality in the reservoir. The concentrations of NO3-N and PO4-P were high enough to stimulate phytoplankton growth. Conservatory measures need to be enforced to reduce the rate of siltation and further pollution of the reservoir arising from the human activities in the catchment of the Saminaka reservoir.