Getso Balarabe Usman , Maryam Murtala Badamasi, Isah Abubakar

Keywords: River Niger, Phytoplankton, Diversity indices, Kogi state

Abstract

Background: Aim: This study was carried out to evaluate changes in phytoplankton abundance and species composition as a reflection of the ecological status of a catchment on river Niger over a period of 12 years. Method: Water samples were analysed in both dry and wet seasons of the years 1999 and 2011 for phytoplankton. Diversity indices were used to analyse the data. Results: Buldalphia regia accounted for the most number of species (21) in the dry season of the year 1999. While Skeletonema sp. accounted for the most number of species (298) in the wet season. In 2011 Nitzschia acicularis and Dictyosolen fragilissimus both contributed 14 species each accounting for the most species in the dry season and wet season respectively. Species abundance in 1999 was highest (1,852 cells/ml) in the wet season. Bacillariophyta accounted for (1,210 cells/ml) and (50 cells/ml) in wet and dry seasons of the year 1999. Also, in 2011 Bacillariophyta accounted for the most individuals (69 cells/ml) and (63 cells/ml) in the wet and dry seasons respectively. Diversity indices showed that Bacillariophyta had the highest Taxa_S (21) at STA in 1999. Shannon_H and Simpson_1-D indices showed diversity of 2.23 and species evenness of 0.87 at STB in 2011. In Cyanophyta, dominance was highest at STA in the year 2011. The result of this study showed significant changes in the phytoplankton size-class abundance and species composition of the lower Niger River over a period of 12 years. The catchment under study was polluted with Cyanophyta in the year 1999 and Pyrrophyta in 2011.