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Please use this identifier to cite or link to this item: http://hdl.handle.net/123456789/24

Date Added: 31-Aug-2007
Abstract: The temporal dynamics of biomass and photosynthetic production of phytoplankton in relation to some physico-chemical environmental variables were studied at two stations, central (C) and near-shore (Sh) in Lake Hora- Arsedi from July 2005 to April 2006. The phytoplankton community Lake Hora-Arsedi was dominated by blue-green algae although green algae and diatoms were also quantitatively important. Blue-green algae were abundant during the period extending from October, 2005 to February, 2006 while diatoms and green algae became more important during periods of precipitation (August-September, 2005 and March-April, 2006). The phytoplankton biomass varied from 19.1 to 47.6 (mean =33.42) and from 21.5 to 53.15 (mean = 37.47) mg m-3 at the central and near-shore stations respectively. The vertical distribution of photosynthetic activity was of a typical pattern for phytoplankton with light-inhibition at the surface on all sampling dates. Light-saturated rate of photosynthesis (Amax) ranged from  473 to 1230 mg O2 ( 147.6 to 383.8 mg C) m-3 h-1) at the central station. Lack of correspondence between phytoplankton biomass and Amax was apparent. Biomass-specific rate of photosynthetic production at lightsaturation, photosynthetic capacity (Pmax) ranged from 13.6 to 52.8 mg O2 11 (mg Chl a)-1 h-1 at the central station. An inverse relationship between photosynthetic capacity (Pmax) and phytoplankton biomass (B) was also observed. The hourly integral photosynthetic rate (A) ranged 0.41 to 2.0 g O2 ( 0.128 to 0.62 g C) m-2 h-1 and the R2 value shows that biomass explains 0.4% of the variance in A. The daily integral photosynthetic rates ((A ) estimated ranged from 3.0 to 18.0 g O2 ( 0.94 to 5.62 g C ) m-2 d- 1.The temporal variations in the taxonomic composition, biomass and primary production of phytoplankton are discussed in relation to some physico-chemical and biological variables.
Description: I am profoundly indebted to my research advisor, Dr. Demeke Kifle for his unreserved advice and invaluable help at all times. Without his generous help and support, completion of my study would have been impossible. It is a real pleasure for me to acknowledge my indebtedness to my stream advisor Dr. Seyoum Mengistu, who was always ready to assist. My deepest appreciation goes to my colleague Solomon Abebe for his friendship throughout the study period. I gratefully acknowledge the invaluable cooperation of the chairman and secretaries of the Department of Biology. I am thankful to the School of Graduate Studies at Addis Ababa University for funding my research project. My heartfelt gratitude is due to Somali Regional State Education Bureau for sponsoring me to pursue postgraduate studies. I am also grateful to Ato Yeneneh Mamo (boatman) for his invaluable cooperation and genuine companionship during the field work. I gratefully acknowledge Addis Ababa Water and Sewerage Authority Central Laboratory Service for the analysis of nutrients (NO3-N). I also wish to thank the National Meteorology Agency for the provision of rainfall and air temperature data of the study area. Special thanks to my parents, my father Ato Wondale Taye and my mother W/ro Amognesh Yimer, for (not so) silently suffering through my characteristic ways. I also acknowledge all my colleagues in Fisheries and Aquatic Sciences Stream. Finally and most importantly, endless thanks to my children, Beth-el Abebaw, and Yabetse Abebaw who are the sole source of motivation and encouragement, are highly appreciated for their patience in my absence for so long a time. I praise Jesus Christ my Lord for giving me the strength to withstand all ups and downs.
URI: http://hdl.handle.net/123456789/24
Appears in:Thesis - Biology

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