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A Seasonal Study on Phytoplankton Primary Production in Relation to Light and Nutrients in Lake Ziway (Ethiopia)

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dc.contributor.advisor Belay, Amha (PhD)
dc.contributor.author Tilahun, Girma
dc.date.accessioned 2018-07-02T06:54:10Z
dc.date.available 2018-07-02T06:54:10Z
dc.date.issued 1988-06
dc.identifier.uri http://etd.aau.edu.et/handle/123456789/5190
dc.description.abstract Primary production by phytoplankton of Lake Ziway, Ethiopia, was st.udied from February. 1987 to Fehruary.1988 by the oxygen light-dark bottle technique. Supporting information included data on thermal characteristics, water chemistry, light penetration and meteorological conditions. Isothermal or near isothermal conditions ~Iere fr~quently observed. These were ensured by ~Iindy condition prevail ing on the large and unsheltered lake surface. I'lell oxygenated water from top to bottom provided evidence for frequent mixing. In all the sampling periods sodium clearly dominated the cations and carbooate-bic~rbD~Nte rlnmi~tQd the anions. The cationic proportion of the lake followed the order Na » Ca > f1g > K \'Ihile its aniont.c proportion fnl..l..owed the order HC03- + C03= » CD S04. The lake \'las found to have a htgh concentratIon of siHca and low concentrations of phosphate ond nitrate. The pattern of underwater light penetration was similar in all the sampling periods. The highest penetration occurred in the red, and the 10~lest in the blue spectral region. Solar irradiance incident on the lake surface di d not va ry markedly except for the 10\'1 va lues record(:d on cloudy days. The maximum photosynthetic rates of bottled phytoplankton varied between 1640 and 4070 mg 02.m-3.h-1 and areal rates ranged from 288 to 1625 mg 02m-2h-l. A principal reason for high rates of photosynthesis WIIS the combined effect of high chlorophyll .i!. content of the euphotic zone (81.1- 191.6 mg ChI lI.m- 2 ) and high photosynthetic capacity 1I1.0 - 22.5 mg 02 (mgChla)-1 h-I ) Efficiency of utilization of photosynthetically available radiation (Ph.A.R), Q, ranged from 2.4 to 9.6 mmol 02 per Einstien Ph.A.R. incident on the lake surface. An inverse relation bet\'leen efficiency and irradiance ~Ias observed. The temporal variation in al gal biomass was more pronounced when measured on a per unit area basis (cv R 23.9%), than when measured on a per unit volume basis (cv = 10.1%). This \'las due to the marked variation in the underwater light climate of the lake. High algal. biomass and sustained product ion seem8d to be maintained more by nutrient recycl ing than by nutrient input as the lake \'las of 10\'1 nutrient status through out the year. Hydrographic (wat2r column structure) factors seemed to play an over riding role in determining the rate of nutrient recycling, the lIndOrl'later light climate, the nxtent of algal gro\'lth in the lake, and subsequently the spatial (vertical) and temporal pattern of phytoplanktonic photosynthesis. en_US
dc.language.iso en en_US
dc.publisher Addis Ababa University en_US
dc.subject Biology en_US
dc.title A Seasonal Study on Phytoplankton Primary Production in Relation to Light and Nutrients in Lake Ziway (Ethiopia) en_US
dc.type Thesis en_US

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