Browsing by Author "Kifle, Demeke(PhD)"
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Item Plankton Communitiy Structure and Interactions in a Cyanobacteria-Dominated Tropical Reservoir (Koka, Ethiopia)(Addis Ababa University, 2016-06) Major, Yeshiemebet; Kifle, Demeke(PhD)Koka is a large multi-purpose reservoir impacted by the ever-increasing human activities that resulted in its enrichment with algal nutrients and contamination with chemicals of industrial origin. With a view to come up with scientific information usable in the protection of aquatic resources and public health, temporal dynamics of the community structure and interactions of the major plankton components (phytoplankton and zooplankton) in relation to selected physico-chemical parameters were investigated at monthly intervals from May, 2013, to April, 2014. The observed exceedingly low ZSD, which may have partly resulted from particles resuspended in the water column by windgenerated turbulence to which shallow water bodies like Koka Reservoir are especially susceptible, indicates the remarkably high turbidity of the reservoir. The levels of inorganic nutrients recorded for Koka, which are quite high in comparison to those of Ethiopian rift valley and highland lakes, are typical of reservoirs, which, unlike natural lakes, have large phosphorus and nitrogen loads. The mean values of total phosphorus (0.27 mg L,I), chlorophyll-a (85.79 J.lg L'I), and transparency (0.15 m) recorded for Koka Reservoir WaJTant its classification as a hypereutrophic water body characterized by high biomass production and elevated concentrations of nutrients. The phytoplankton community in the reservoir was constituted by a total of 89 species with the larger number of species belonging to the Chlorophyceae (34) and Cyanophyceae (28). Cyanobacteria were the most important taxa both in terms of \' II l abundance and biomass, with Microcystis and Cylindrospermopsis species altemately dominating the phytoplankton community and accounting for up to 72.29% and 62.87 % and 21.45. % and 20.23% of the total phytoplankton abundance and biomass as biovolume, respectively. The mean concentrations of chl-a (~g L-1) of the nano- (2-20 ,um, 39) and net- (>20 ,um, 40.4) phytoplankton were much higher than those of the picophytoplankton (10.48) as would be expected considering the level of eutrophication of the reservoir. The composition and abundance of cyanobacteria and their toxins, microcystins (MCs) and cylindrospermopsins (CYN), were investigated using samples collected at monthly intervals from the Amudde side of Koka Reservoir from May, 2013, to April, 2014. Analyses of cyanotoxins in filtered samples by HPLC-DAD and LC-IMSIMS identified and quantified 5 variants ofMCs (MC-RR, MC-YR, MC-dmLR, MC-LA and MC-LR) in all samples, with their total concentrations ranging from 1.86 to 28.3 ~g L -I and from 1.71 to 33 ~g L -I, respectively and greatly surpassing WHO's drinking water guideline value of 1 ~g L-1 • The maximum level of MCs occurred in December, 2013, when the phytoplankton community of the reservoir was constituted almost entirely by Microcystis aeruginosa. The total concentrations of MCs measured in freeze-dried plankton samples by HPLC-DAD and LC-MSIMS varied between 312 and 641 ~g (g dwtrl and 351 and 709 ~g (g dwtrl, respectively. Thus to prevent intoxications continuous monitoring of these reservoirs is strongly recommended. This has to be taken into consideration in the management of the reservoir when it used for various domestic purposes. Studies regarding the prediction of the occurrences of toxic blooms and their toxins must be implemented and strengthened in the future in order to avoid or reduce the potential risks associated with human and animals' exposure to the toxins. Despite the presence and occasional abundance of Cylindrospermopsis spp., cylindrospermopsin was not detected by HPLC-DAD and LC-MSIMS in any of the samples collected tlu'oughout the study period. Analysis of the zooplankton community in the reservoir revealed a total of 52 species, 25 of which are new records for Koka Reservoir. With 40 species, rotifers were the most ii I,' \i \' species-rich group followed by cladocerans (8 species), and copepods (4 species). The rotifer Keratella tropica was the species recorded with the highest abundance among the zooplankton taxa contributing 42.11 % of total rotifers abundance. The cladocerans were dominated by small species, Ceriodaphnia corn uta, Diaphanosoma excisum and Moina m/crura, with rare occurrence of the large cladoceran D. barbata during a few months of the sampling period. Total abundance of copepods was constituted largely by Thermocyclops decipiens, which is the most commonly dominant species in tropical inland waters. Calanoid copepods were represented by a single species; Tropodiaptomus sp. Zooplankton abundance was generally higher during the dry season than the rainy season. Eutrophication of Koka Reservoir has resulted in the dominance of cyanobacteria, which are generally regarded as unsuitable food source for zooplankton. It was, therefore, hypothesized that seston may playa role in the diet of the zooplankton community of this reservoir. The contribution of seston fractions (<20 11m, ::::20Item Temporal and Spatial Variations in Biomass and Photosynthetic Production of Phytoplankton In Lake Chamo, Ethiopia(Addis Ababa University, 2004-06) Shumbulo, Eyasu; Kifle, Demeke(PhD)The temporal and spatial variations in the biomass and photosynthetic production of phytoplankton in relation to some physico-chemical environmental factors were investigated at two (offshore and near-shore) stations in Lake Chama from August, 2003 to May, 2004. Inorganic nutrients varied temporally, with their low and high concentration levels generally corresponding to the dry and rainy periods respectively. Lake's transparency was always low (ZSD < 40 cm). Because phytoplankton biomass was high throughout the study period, its contribution to the extinction of underwater light is expected to be considerable. Phytoplankton biomass measured as chlorophyll a varied 43 to 95 (mean = 77.2) and 47 to 108 (mean=69.4) mg Chi a m-3 at the near-shore and central stations, respectively. The vertical distribution of photosynthetic activity was of a typical pattern for phytoplankton with light-inhibition on all sampling dates. The light-saturated rate of photosynthesis (Amax) ranged from 721 to 1789 mg O2 (""224.95 to 558.17 mg C) m-3 h-1 at the central station and from 543 to 1803 mg 02( ""169. 42 mg C) m-3 h-1 at the near-shore station. Lack of correspondence between phytoplankton biomass and Amax was evident. Biomass-specific rate of photosynthetic production at light-saturation, photosynthetic capacity (¢max) ranged from 9 to 34 mg O2 (mg Chi ay-1 h-1 at the nearshore station and from 10 to 34 mg 02 (mg Chi ay-1 h-1 at the central station. An inverse relationship between photosynthetic capacity and phytoplankton biomass was also observed. Hourly integral photosynthesis ranged from 0.36 to 1.72 g 02 ("" 0.11 to 0.54 g C) m-2 h-1 at the central station and from 0.47 to 1.8 g 02 ("" 0.15 to 0.56 g C) m-2 h-1 at the near-shore station. The production rate per unit area seems to have been influenced by the light-saturated rate of photosynthesis as the strong and positive correlation between the two (r = 0.77) suggests. The temporal variations in phytoplankton biomass and primary production in relation to environmental factors are discussed with a view to identify those environmental variables that have regulatory role. Key words: Biomass, production, phytoplankton, Lake Chama, Ethiopia,Item Temporal Dynamics of Phytoplankton Biomass and Primary Production in Relation To Some Physico-Chemical Variables in Lake Hora-Arsedi, Ethiopia.(Addis Ababa University, 2006-06) Wondie, Abebaw; Kifle, Demeke(PhD)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 (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.Item Temporal Dynamics of Water Quality and Community Structure and Photosynthetic Production of Phytoplankton in Belbela Reservoir, Ethiopia(Addis Ababa University, 2011-06) Girma, Feyisa; Kifle, Demeke(PhD)The temporal dynamics of the composition, abundance, biomass and photosynthetic productivity of phytoplankton in relation to physico-chemical water quality and zooplankton were studied from September, 2010 to May, 2011 in Belbela reservoir. Water transparency exhibited temporal variation (0.16 m to 0.26 m), which was primarily determined by abiogenic turbidity. The depth profiles of temperature and dissolve oxygen seem to indicate the absence of deep-seated and persistent thermal stratification, which is consistent with the shallowness and complete exposure of the reservoir to wind action. Aggregate chemical parameters were clearly indicative of the very dilute nature of the reservoir water. All nutrients except soluble reactive phosphate were generally at high levels. All chemical parameters including inorganic nutrients exhibited temporal variations with no obvious association with biological variables. The phytoplankton community of the reservoir was primarily constituted by bluegreen algae, green algae and diatoms, with the overwhelming dominance of blue-greens whose dominance seemed to be favored by the turbid, turbulent and nutrient-rich water column. The major contributors to the dominance of blue-green algae include the potentially toxic taxa Cylinderospermopsis, Microcystis and Planktothrix. The impact of the rotifer-dominated zooplankton community, on the phytoplankton seemed to have been weakened by the abundant large-sized colonial and filamentous bluegreens, which are not manageable and probably toxic. Chlorophyll a biomass of phytoplankton varied temporally (20.38 -68.57 Ig L-1) with its peaks corresponding to those of total abundance of phytoplankton and blue-greens but without any clear causal relationship with inorganic nutrients. The vertically compressed depth profiles of gross photosynthesis exhibited temporal variations in their lightsaturated rates (Amax) and depths of their occurrence. Amax varied from about 226 to 891 mg O2 (≈70.5 to 278 mg C) m-3 h-1, corresponding to the lowest and highest phytoplankton biomass values although lack of good correlation between the two was evident. The fairly high and positive correlation between Amax and the biomass-specific rate at light saturation, Pmax (r=0.6938, r2=0.4813 at p=0.0563) provided an explanation for the observed association of high light-saturated rates with low algal biomass. Pmax ranged from ≈ 5.5 to 24.3 mg O2 (mg Chl a)-1 h-1 with most values below 15, but with its maximum value higher than that considered as representative for many African lakes [about 20 mg O2 (mg Chl a)-1 h-1] and an upper limit for lakes of the temperate regions. The hourly integral rate of gross photosynthesis (ΣA, mg O2 m-2 h-1) ranged from 0.112 to 0.510 g O2 (≈ 0.035-0.159 g C) m-2 h-1 with its variations being primarily due to temporal changes in Amax (r=0.7551, r2 =0.5701 at p= 0. 0.0303). The present results seem to suggest that the reservoir is at the verge of a seemingly irreversible environmental degradation. There is, therefore, a need for the assessment of cyanotoxins and the impact of human activities like irrigation, shore-line modification and removal of plant cover with a view to develop strategies of preventing further degradation of the aquatic ecosystem and loss of its resources.