EFFECTS OF PHYSICO-CHEMICAL FACTORS ON SEASONAL DYNAMICS OF THE PHYTOPLANKTON IN NGURU LAKE, NORTHEASTERN NIGERIA.

Studies were conducted in Nguru Lake between May 2006 and April 2008 to map temporal changes in phytoplankton composition and attempt to relate these changes to physico-chemical parameters in the ecosystem. Temperature, conductivity and alkalinity showed significant spatial variation. Nutrients showed significant seasonal variation. Twenty five phytoplankton genera were recorded. Green algae (Chlorophyta) were the most dominant contributing 46% of the total biomass followed by blue green algae-Cyanophyta(29%), Bacillariophyta(22%) and Dinophyta(2%). Seasonal changes were observed for the three major plant nutrients total phosphorus (PO­4-P) ranged from 5.2 -9.6mg/l. Total nitrogen (NO3-N) ranged from 2.4-12.8mg/l and sulphates ranged from 1.0-10.1mg/l. wide variations in environmental variables were observed in the lake. Results obtained in this study showed that the lake was undergoing gradual eutrophication resulting in deterioration of water quality, decreased fish yield and subsequent reduced income to the local communities. The eutrophication was further aggravated by increasing human and livestock population. Key Words: Biomass, Nguru Lake, Nutrients, Phytoplankton, Water quality