Relation between phytoplankton composition and abundance and physicochemical characteristics of Chepkanga Dam, Eldoret, Kenya

Abstract

Physicochemical characteristics and phytoplankton species composition and abundance (chlorophyll-a concentration) were measured in Chepkanga Dam during the months of November and December (2007) and February (2008); all sampling months being within the dry season. Three sampling sites (A, B and C) were selected to correspond to different anthropogenic impacts. Triplicate water samples were collected twice per month and analysed in the laboratory (chlorophyll- a; phytoplankton species and dissolved oxygen and reactive phosphorus concentrations). In situ measurements of water temperature and pH also were taken at the same sampling sites. A total of 39 phytoplankton species were identified, including 15 Bacillriophyceae species, 12 Chlorophyceae species, 7 Desmidiaceae species and 5 Cyanophyceae species. A two-way ANOVA statistical analysis indicated significant differences between months (among stations) for physicochemical parameters (P < 0.05), although insignificant changes were observed between stations (among months) (P > 0.05). Phytoplankton species (e.g., Ankistrodesmus falcatus, Staurastrum sp. and Pediastrum sp.) appeared and disappeared between the study months of November to February (Table 1), implying that monthly variations among physicochemical characteristics influenced the phytoplankton abundance, as the different phytoplankton species exhibit different environmental selectivity.