Temporal Dynamics of Biomass and Primary Production of Phytoplankton In Relation to Some Phsico-Chemical Factors In Lake Koriftu, Ethiopia
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Date
2007-07
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Addis Ababa University
Abstract
Biomass and Photosynthetic productivity of phytoplankton in relation to the physical and
chemical conditions of the water column in Lake Kuriftu were studied from August, 2005
to April 2006. All the physical, chemical and biological parameters measured varied
spatially and temporally. The Lake’s transparency (ZSD) was always less than 0.6 m with
smaller values coincident with periods of rainfall and negatively correlated (r=-0.36)
with phytoplankton biomass. The chemistry of the lake was basically similar to the dilute
East African lake waters, with maximum pH and total alkalinity values of 8.8 and 3.1
meq/l respectively. The inorganic nutrients, which were of moderately high levels varied
temporally as a function of hydrological, hydrographic and biological conditions of the
lake. The phytoplankton community which was consistently dominated by cyanobacteria
exhibited low species diversity. Phytoplankton biomass measured as chlorophyll a varied
from 18.35 to 45.18 mg Chl a m-3 at the near-shore station and from 17.24 to 55.6 mg Chl
a m-3 at the central station. The light-saturated rate of photosynthesis (Amax), which was
positively and strongly correlated with phytoplankton biomass, ranged from 571 to 1136
mg O2 m-3 h-1. Biomass-specific rate of photosynthetic productivity at light saturation
(Pmax) ranged from 18.78 to 33 mg O2 (mg Chl a)-1h-1, while the hourly integral
photosynthetic production (ΣA) which was positively and strongly correlated with
biomass and Amax, varied between 0.686 and 1.05 g O2 m-2 h-1. The factors responsible for
the observed spatio-temporal variations in the physical,chemical and biological features
of the lake are discussed.
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Biology