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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/2477

Authors: Nigatu, Ebisa
Advisors: Dr. Demeke Kifle,
Copyright: Jun-2010
Date Added: 4-May-2012
Abstract: ABSTRACT Dynamics of phytoplankton and physico-chemical parameters of water quality were studied in Geffersa Reservoir from October, 2009 to June, 2010 using samples collected at bi-weekly intervals. Secchi depth (vertical visibility) varied from a minimum of 0.20 of the minor rainy season to a maximum of 0.66m during the dry period. Turbidity, which fluctuated between 7.2 and 189 NTU, exhibited a seasonal pattern, which was more or less similar to that of phytoplankton biomass measured as Chl a (r= 0.649, r2= 0.415 at p= 0.0070). The concentrations of NO3-N, NH3 + NH4+- N and Soluble Reactive Phosphate (SRP) varied from 10.0 to 300, 146 to 866 and 29 to 201 μg L-1 respectively while Molybdate-reactive silica ranged from 2.5 to 13.4 m L- 1. Turbidity, TDS, and other chemical parameters were found to be far below the upper permissible limits for drinking water supply sources. The phytoplankton community whose species diversity was found to be low was primarily constituted by green algae, blue-green algae and diatoms, the contributions of the species-rich green algae ranging from 1 to 95 % and with major species belonging to the genera Crucigenia, Kirchneriella and Ankistrodesmus. The second and third most abundant algal groups were the blue-green algae and diatoms, which were dominated by two species of Microcystis, M. aeruginosa and M. panniformis. and by a species of the filamentous genus Melosira, M. agassii, followed by Fragilaria capucina and Rhopalodia gibberulla. Among the flagellate groups, dinoflagellates were the most important, with Peridinium cinctum and P. bipes as the quantitatively most important species. Among the cryptomonads, Cryptomonas marsonii and C. ovata were found in large numbers, Chl a biomass of phytoplankton averaged 12.41 μg L-1 and varied from a minimum of 2.29 μg L-1 to a maximum of 40.67 μg L-1 with its fluctuations being correlated more with ammonia +ammonim (r =0.662, r2 = 0.44 at p=0.0045) than with nitrate (r=-0.4093, r2= 0.1675 at p= 0.1028) or phosphate (r= 0.435, r2=0.289 at p= 0.0800). Rotifers were the most abundant and species-rich zooplankton group with mean percentage contributions of 66.82 while the contributions from copepods and cladocerans were 24.51% and 8.67% of the total abundance of the zooplankton respectively. The causal relationships among physicochemical and biological variables are discussed and recommendations made.
URI: http://hdl.handle.net/123456789/2477
Appears in:Thesis - Biology

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