Spatial and temporal variation in community structure of phytoplankton in chebara reservoir-Kenya

River impoundments create reservoirs for many of varying, sizes which serve one or more functions, and change transform lotic aquatic systems to lentic ones, with changes in physical and chemical properties, biotic assemblage and productivity. Chebara reservoir is located at 36o E and 22o S and situated within Elgeyo-Marakwet County. The reservoir was formed as a result of damming the Moiben River to supply water to Eldoret town. A study was conducted on composition and relative abundance of phytoplankton in the reservoir from December 2007 to April 2008. Sampling was done every month at six stations distributed over the reservoir; one station at inlet of Moiben River, one station at the outlet, three at minor inlets and one within the reservoir. Phytoplankton were collected using a 28nm diameter plankton net immersed vertically below the photic depth. Photic depth was measured using 25cm diameter Secchi disk. Phytoplankton were identified and enumerated using a compound microscope. All statistical analyses were performed with STATIGRAPHIC 2.1 Plus and STATISTICA 6.0 procedures. Six phytoplankton classes were identified which included Cyanophyceae (22 genera) Bacillariophycae (25 genera), Chlorophyceae (55 genera), Euglenophyceae (3 genera), Rhodophyceae (2 genera) Pyraphyceae (6 genera) and Crysophyceae (8 genera) similar to observations made in tropical oligotrophic lakes. The order of abundance was Pyraphyceae> Cyanophyceae> Chlorophyceae> Bacillariophyceae> Crysophyceae>Euglenophyceae>Rhodophyceae. Members of the Class Chlorophyceae showed the highest species diversity and abundance. The results obtained from this study can be used track the effects of catchment land use in the drainage basin investigate the cumulative, long term effects of climate change, and river impoundment on the algal evolution.