Temporal Changes in the Community Structure and Kotosynthetic Production of Phytoplankton in Lake Babogaya, Ethiopia
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Date
2006-07
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Addis Ababa University
Abstract
The temporal variations in the taxonomic composition, biomass and
photosynthetic production of phytoplankton in Lake Bishoftu-Guda were
investigated for a period of one year, from November, 2004 to October,
2005. Concurrently changes in some physico-chemical environmental
variables were studied. Temporal variations in inorganic nutrients were
observed with the maximum values cOinciding with a period of relatively
high rainfall at both stations. Lake's transparency was always high (ZSD
> 1m). Since the lake was transparent due to low phytoplankton
biomass and suspended inorganic particles throughout the study
period, the extinction of underwater light was low. The phytoplankton
community of this nutrient-poor and deep lake was dominated by
dinof/agllates during the dry and short rain periods before a shift in
dominance to diatoms occurred during the long rainy period.
Phytoplankton biomass of Lake Bishoftu-Guda was found to vary from 4
to 20 (mean=1O.8) mg Chi a m-3 at the central station and from 3.96 to
24.2 (mean=lO. 2) mg Chi a m-3 at the near-shore station. The depthprofiles
of gross photosynthetic activity were of a typical pattern for
phytoplankton with light-inhibition at the surface and with light-saturated
rates generally occurring at a depth of 0.9 m of the water column on all
sampling dates. The light-saturated rates of photosynthesis (Amax)
ranged from 106 to 407 mg O2 (-33.1 to 127 mg C) m-3 h-I. A strong
and positive correlation (r=0.76, p=O.OOO) was found between Amax and
phytoplankton biomass. Biomass-specific rate of photosynthetic
production at light-saturation (Pmax) ranged from 19 to 29 mg O2 (mg chi
arl h-I and was inversely related to phytoplankton biomass. Hourly integral photosynthesis (LA, g d m-2 h-I
), which was obtained by the
Grid Enumeration Analysis ranged from 0.112 to 0.66 g O2 (-0.03 to
0.21 g C) m-2 h-I. There was a positive but weak correlation (0.36),
P=O.OOO) between phytoplankton biomass and hourly integral
photosynthesis, while the correlation between LA and Amax was 0.83.
Daily production rates per unit area (LlA g d m-2 efl), were estimated
from hourly integrated rates and the calculated daily integral production
values ranged from 1.01 to 5.98 g O2 (-0.32 to 1.87 g C) m-2 efl. The
temporal variations in species composition, biomass and photosynthetic
production of phytoplankton are discussed in relation to physicochemical
factors.
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Biology