A Seasonal Study On Phytoplankton Primary Production In Relation To Light And Nutrients In Lake Ziway (ethiopia)

Primary production by phytoplankton of Lake Ziway, Ethiopia, was st.udiedrnfrom February. 1987 to Fehruary.1988 by the oxygen light-dark bottlerntechnique. Supporting information included data on thermal characteristics,rnwater chemistry, light penetration and meteorological conditions.rnIsothermal or near isothermal conditions ~Iere fr~quently observed.rnThese were ensured by ~Iindy condition prevail ing on the large andrnunsheltered lake surface. I'lell oxygenated water from top to bottomrnprovided evidence for frequent mixing.rnIn all the sampling periods sodium clearly dominated the cations andrncarbooate-bic~rbD~Nte rlnmi~tQd the anions. The cationic proportion of thernlake followed the order Na » Ca > f1g > K 'Ihile its aniont.c proportionrnfnl..l..owed the order HC03- + C03= » CD S04. The lake 'las found to have arnhtgh concentratIon of siHca and low concentrations of phosphate ondrnnitrate.rnThe pattern of underwater light penetration was similar in all thernsampling periods. The highest penetration occurred in the red, and thern10~lest in the blue spectral region. Solar irradiance incident on the lakernsurface di d not va ry markedly except for the 10'1 va lues record(:d on cloudyrndays.rnThe maximum photosynthetic rates of bottled phytoplankton varied betweenrn1640 and 4070 mg 02.m-3.h-1 and areal rates ranged from 288 to 1625 mgrn02m-2h-l. A principal reason for high rates of photosynthesis WIIS therncombined effect of high chlorophyll .i!. content of the euphotic zone (81.1-rn191.6 mg ChI lI.m- 2 ) and high photosynthetic capacity 1I1.0 - 22.5 mg 02rn(mgChla)-1 h-I ) Efficiency of utilization of photosynthetically available radiationrn(Ph.A.R), Q, ranged from 2.4 to 9.6 mmol 02 per Einstien Ph.A.R. incidentrnon the lake surface. An inverse relation bet'leen efficiency and irradiancern~Ias observed.rnThe temporal variation in al gal biomass was more pronounced whenrnmeasured on a per unit area basis (cv R 23.9%), than when measured on a perrnunit volume basis (cv = 10.1%). This 'las due to the marked variation inrnthe underwater light climate of the lake. High algal. biomass and sustainedrnproduct ion seem8d to be maintained more by nutrient recycl ing than byrnnutrient input as the lake 'las of 10'1 nutrient status through out the year.rnHydrographic (wat2r column structure) factors seemed to play an overrnriding role in determining the rate of nutrient recycling, the lIndOrl'laterrnlight climate, the nxtent of algal gro'lth in the lake, and subsequently thernspatial (vertical) and temporal pattern of phytoplanktonic photosynthesis.

Get Full Work

Report copyright infringement or plagiarism