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Title: Spatio- Temporal Variations of the Biomass and Primary Production of Phytoplankton in Koka Reservoir
Authors: Hadgembes, Tesfay
Date Added: 21-Sep-2007
Abstract: The temporal and spatial changes in the biomass and primary production of phytoplankton in the turbid, frequently mixing eutrophic Koka Reservoir were studied from August, 2005 to April, 2006.The physico – chemical and biological features of the lake varied temporally and spatially during the study period. Inorganic nutrients, which remained at high levels throughout the study period, varied temporally with their low and high concentration levels generally corresponding to the dry and rainy periods of the year, respectively. The phytoplankton community in the reservoir was dominated persistently by Cyanophyceae, which were largely constituted by Microcystis spp. accounting for over 50% of the abundance of the phytoplankton assemblage on all sampling occasions except in February, 2006 when the diatom Aulacoseira granulate became dominant. The surface chlorophyll a concentrations ranged from 20.85 to 221.01, 11.47 to 69.5 and 4.86 to 54.9mg m-3 at the littoral, offshore and Awash River mouth Stations, respectively, with seasonal maximum in December, 2005 at all stations coincident with the bloom of Microcystis spp. The vertical distribution of photosynthetic activity was a typical pattern for phytoplankton with light-inhibition on all sampling dates. The light-saturated rate of photosynthesis (Amax) ranged from 350 mgO2 m-2h-1 of August to 1169 mg O2 m-2h-1 of December, 2005 coinciding with low and maximum phytoplankton biomass, respectively. The biomass - specific rates of photosynthesis (Pmax) ranged from 19.4-37.5 mg O2 (mg Chl a) h-1 . Hourly integral photosynthesis (ΣA) ranged from 0.15 –0.41g O2 m-2 h-1 (≈ 0.056 to 0.154 g C≈) with highest seasonal peaks coinciding with the seasonal maximum of phytoplankton biomass. Light utilization efficiency of the phytoplankton assemblage of Koka Reservoir varied from 0.07 to 0.25 %. The temporal and spatial variations in phytoplankton biomass and primary production seem to be linked to the hydrological and hydrographic conditions of the reservoir. Factors responsible for the observed variations in the physico–chemical and biological conditions of the reservoir are discussed and appropriate conservation strategies for the reservoir are recommended.
Description: A thesis presented to the School of Graduate Studies Addis Ababa University In partial fulfillment of the requirement for the Degree of Master of Science in Biology
URI: http://hdl.handle.net/123456789/136
Appears in:Thesis - Biology

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