Temporal Dynamics of the species composition and Size fractionated Biomass of Phytoplankton in Lake Kuriftu, Ethiopia

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The temporal dynamics of phytoplankton and physic-chemical variables were studied at a central station of Lake Kuriftu from December, 2008 to November, 2009. The lake is shallow and as a result undergone complete mixing throughout the study period. Secchi depth ranged from 0.21 m to 0.6 m. The Lake’s transparency (ZSD) was always less than 0.6 m with smaller values coincident with high phytoplankton biomass even though there is weak correlation b/n phytoplankton biomass and ZSD. The chemistry of the lake was basically similar to the dilute East African lake waters, with maximum pH and total alkalinity values of 9.09 and 4.1 meq/l respectively. Nitrate concentration (μg L-1) ranged from a minimum of 9.33 in November, 2009 to 65.45 in April, 2009. Soluble reactive phosphate- phosphorus (SRP, in μg L-1) varied from a minimum value of 14.65 in January, 2009 and May, 2009 to a maximum of 402.57 in August, 2009. Dissolved silica (Molybdate-reactive silica, SRSi in mg L-1) ranged from 3.051 in December, 2008 to 97.92 in September, 2009. The phytoplankton community which was dominated by Cyanobacteria is 2nd in diversity to chlorophycea which covers 25 species of the 50 species. Cylinderospermopsis Africana was the most dominant species throughout the study period.The diversity index was narrow ranging from 1.24 -6.42 bits/individual. Among the three size-group of phytoplankton, the nanoplankton (2-20 μm) was the most important contributor to the total phytoplankton biomass with its biomass and percentage contributions to the total phytoplankton biomass ranging from 15.44 μg L-1and 51.93 % to 19.74μg L-1 and 73.84 % respectively. The Chl a biomass and percentage contribution to total phytoplankton biomass of the Netplankton and Picoplankton varied from 1.94 to 6.73 and 6.53 % to 13.87% and 4.68 to 14.63 and 17.5% to 41.54 % respectively. The factors responsible for the observed spatiotemporal variations in the physical,chemical and biological features of the lake are discussed. Key words: Lake Kuriftu, Size fractionated Biomass, Phytoplankton, Temporal Variation.



Lake Kuriftu, Size fractionated Biomass, Phytoplankton, Temporal Variation