Browsing by Author "Kifle, Demeke (PhD)"
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Item Aquatic Ecosystems and Environmental Management Water Quality of Akaki Rivers and Its Impact on Irrigated Vegetable Farms(Addis Ababa University, 2018-06-03) Atalay, Kassahun; Kifle, Demeke (PhD)Urbanization, industrialization and agricultural development practices are the main causes for the environmental degradation of surface waters including rivers. The highly impacted Akaki River, the subject of the present study, is being used for irrigation, watering livestock, sanitation and other domestic purposes. This represents a serious threat to public health and life of aquatic and terrestrial organisms. Thus, with the view of gathering information usable in the development of strategies of protection of this aquatic resource, physico-chemical and microbial water quality parameters of the irrigation water, irrigated soils and leafy vegetables cultivated on them were assessed from March to August, 2017. The biotic transfer factor (TF) and Target Health Quotient (THQ) for all measured metals were also calculated. The observed levels of Turbidity, TSS, TDS, TP, and Nitrite surpassed the acceptable levels set for domestic use and general water quality assessment criteria. DO and BOD5 levels also failed to comply with the safe limits set for aquatic life and general water quality assessment criteria. The levels of Faecal coliforms, Fe, Mn, Cu, Zn and Cr surpassed the maximum levels recommended for the safe use of wastewater for irrigation of vegetables. Vegetable farms in and around Addis Ababa, which were irrigated with the polluted waters of Akaki River exhibited concentrations of Zn, Cr, Cd and Cu in the soils of farm plots and of Fe, Zn, Cr, Ni, and Pb in vegetables grown on them that surpassed the safe limits recommended by international organizations. The potential health risk indicator (THQ) for Fe, Mn, Pb and Cd also reached values above 1, suggesting that they may pose health effect on consumers. The present findings suggest the need for immediate measures to protect consumers and the aquatic resource.Item Assessment of the Effect of Artisanal Gold Mining on Heavy Metals Concentrations and Associated Potential Public Health Risk: The Case of May Sieley River of the Shire , Tigray, Region Ethiopia(Addis Ababa University, 2021-02-19) Elias, Habineza; Kifle, Demeke (PhD)Artisanal gold mining (AGM), in third world countries including Ethiopia has become a livelihood diversification strategy, which makes significant contribution to poverty alleviation. Although artisanal gold mining provides enormous economic benefits, the mining activities are carried out at the expense of the environment and public health due to pollution with heavy metals (HMs). The protection of public health and aquatic resources necessitates the availability of scientific information on pollution with heavy metals. The present study was, therefore, conducted to investigate the efffect of artisanal gold mining on the levels of selected heavy metals in May Sieley River (Tigray) and evaluate the potential human health risk. Surface sediment and water samples were collected from upstream, midstream and downstream sites (USS, MSS &DSS) respectively, during the dry and post-rainy periods and were analyzed for Pb, Cd, Cu, As, Cr, Hg, Ni, and Zn by Inductively Coupled Plasma-Optical Emission Spectrometry (ICP-OES). The concentrations of heavy metals in water samples were compared with WHO and Ethiopian standards for drinking water and assessment of human health risk was made following the guidelines provided by the US Environment Protection Agency. Temperature, pH and dissolved oxygen were measured insitu and were found to be within acceptable ranges and did not show large variations. The differences in HMs concentrations in water among sampling sites during both seasons were not marked except for Cu and Zinc in dry season, although Zn, Cu, Hg, Cd and Pb were higher at the MSS suggesting the association of their levels primarily with AGM. The differences in the concentrations of all HMs in water samples between seasons were marked. The concentrations of HMs in sediment samples varied markedly between the two seasons. The differences in HMs concentrations in sediments among sampling sites during dry seasons were marked for Cu, Zn, Pb and As while in post-rainy season, differences were not marked except for Ni and Pb. The concentrations of all HMs except Nickel in sediment samples of the dry season were higher at the MSS, while they were higher at USS during the post-rainy season. The present results suggest that both AGM and natural sources associated with the weathering of rocks have made contributions to the metal pollution of May Sieley River. Hg and As were above WHO and Ethiopian standards for drinking water in the dry season in all sampling sites, while Cr, Cd, Pb and As were above the same standards for drinking water in the post-rainy season in all sites, except Hg (in one sample of MSS) and Ni (in one sample of DSS). The HQ values for As, Pb, Hg and Cd for both age groups were at unacceptable non-carcinogenic potential health risk levels (HQ>1), while As and Cd for adults and As, Cd and Hg for children, are likely to have chronic effects (Q>10). The Sum of HQs (HI) of analyzed metals was far greater than 1 for both age groups, children being at greater risk. This raises concern about the non-carcinogenic adverse health effects of using the river water for drinking and other household purposes. The results of the ILCR assessment for Arsenic, Lead, Cadmium, Chromium and Nickel indicated that the carcinogenic effect associated with these metals is not acceptable. The study has revealed that the river water is not safe due to HMs pollution, AGM should be managed to reduce its contribution to the pollution of water bodies with heavy metals. The government needs to assist and empower the miners so that they can carry out their activities sustainably and in an environmentally friendly way. Further monitoring of the impact of traditional gold mining on HMs pollution by considering aquatic organisms in order to assess their biomagnification along the food chains is also recommended.Item Dynamics of Phytoplankton and Physicochemical Features of the Ethiopian Soda Lakes Chitu and Shala, and Evaluation of the Potential of their Waters for the Production of Arthrospira (Spirulina) Fusiformis (Cyanophyceae) in Laboratory Cultures(Addis Ababa University, 2015-06) Ogato, Tadesse; Kifle, Demeke (PhD)Soda lakes provide great opportunity for the study and understanding of aquatic ecosystems, owing to their unique biotic assemblage of great ecological and economic values and high sensitivity to environmental changes. In addition, Arthrospira (Spirulina), an alga of high ecological values to soda lakes ecosystems and produced commercially using high-cost chemical medium as a nutritional supplement to humans, grows naturally in some of the soda lakes. In this study, physicochemical features and phytoplankton community of the soda lakes Chitu and Shala, morphology of Arthrospira fusiformis in its natural habitat and its production using waters of the soda lakes were investigated. Measured parameters of underwater light climate of both lakes depicted light-limited conditions, which were associated with the accumulation of Arthrospira in Lake Chitu and non-biological turbidity in Lake Shala. The water column of Lake Chitu exhibited superficial thermal stratification with weak vertical mixing and considerable variability of dissolved oxygen (DO). Lake Shala showed superficial thermal stratification, but with turbulently mixing and well-oxygenated water column. Inorganic nitrogen sources in the euphotic zone of both lakes were often very low or undetectable while phosphorus sources were considerably high, possibly due to their phosphatic mineral-rich rock basins. NH3 and soluble reactive phosphate (SRP) showed dramatic increase with depth in Lake Chitu due to internal loading. SiO2 was remarkably low in both lakes, which was probably associated with biological uptake, some chemical processes within the lakes and organic matter accumulation. The phytoplankton community of Lake Chitu, which was constituted by a few (15) species belonging to the algal classes Bacillariophyceae (60%), Cyanophyceae (26.7%) and Cryptophyceae (2.3%), was dominated by A. fusiformis throughout the annual cycle, accounting for up to 98% of total phytoplankton abundance. The observed high mean phytoplankton biomass (chlorophyll-a, 150 μg chl-a L-1 and dry weight, 0.26 g L-1) in Lake Chitu showed significant seasonality (P < 0.05) with higher levels occurring during the rainy season. The algal biomass and abundance were correlated strongly and positively with rainfall and negatively with alkalinity-salinity, probably suggesting that hydrological control of the salinity of the lake is the major driving force for algal dynamics in Lake Chitu. Phytoplankton community of Lake Shala, which was of relatively higher diversity (23 spp. belonging to Bacillariophyceae, Cryptophyceae, iv Cyanophyceae and Dinophyceae), was persistently dominated by Bacillariophyceae and Cryptophyceae, respectively, accounting for about 57% and 22% of the total number of species, and 28% and 69% of total phytoplankton abundance. Cryptomonas spp. were the most abundant, contributing about 59 to 95% of total phytoplankton abundance of Lake Shala, while Thalassiosira sp. was the second most abundant (1–35%). Although seasonality was not large, the observed variations in the abundance of the dominant species in this lake were associated with water transparency, SiO2, rainfall and its effects on salinity and pH. Mean algal biomass, which was generally low (17 μg chl-a L-1), also showed small seasonal variations in Lake Shala, with strong but inverse relationship with water transparency. In general, the notable variations in phytoplankton and physicochemical parameters in Lake Chitu, probably suggest its sensitiveness to environmental perturbations and that any environmental changes including increased salinization may greatly affect the key alga (A. fusiformis) and the flamingos, with eventual impairment of its ecosystem services. On the other hand, the observed small variations in the physicochemical and phytoplankton variables in Lake Shala seem to suggest the lake‟s resilience to the current level of environmental perturbations, owing to its presumably high stress absorbing capacity associated with its large size and great depth. Three distinct morphotypes of A. fusiformis, tightly coiled (H-type), spiral or loosely coiled (S-type) and intermediately coiled (C-type) were observed in Lake Chitu, with the H-type (50%) and S-type (40%) being the first and second most dominant morphotypes. The dominance of H-type and tightening of its helix pitch were strongly associated with NO3- and HCO3- deficiencies, and high levels of photosynthetically active radiation (PAR) and temperature of the lake, while the abundance of S-type was more strongly but negatively correlated with the high salinity of the lake. The variability in morphology seems to suggest that A. fusiformis undergoes morphological changes in response to environmental stresses in its natural habitat, resulting in the occurrence of various morphotypes of the same species. Comparable growth rate (μ) and biomass (B) of A. fusiformis were observed in both Lake Chitu water-based media (CBM) and Lake Shala water-based media (SBM), with slightly higher values in the latter. Both CBM and SBM supplemented with the standard Spirulina medium (SM) (25% and 50%) supported considerably higher μ and B, which were probably associated with the reduction in pH and salinity, and provision of the limiting nutrient nitrogen in the supplemented media. The higher μ and B in SBM, probably due to some of their aggregate chemical parameters that were closer to those in the SM, and abundant SRP, seems to suggest that Lake Shala water is more conducive to Arthrospira. We contend that 25% and 50%-supplemented Lake Shala water can be preferably used to produce Arthrospira, thereby reducing the cost of nutrients by 75% and 50%, respectivelItem Dynamics of Phytoplankton in Relation to Physico-Chemical Factors in Lake Bishoftu, Ethiopia(Addis Ababa University, 2007-07) Ogato, Tadesse; Kifle, Demeke (PhD)The seasonal dynamics of phytoplankton in relation to some physico-chemical and biological parameters were studied at a near-shore and central stations in Lake Bishoftu from August, 2006 to May, 2007. Water transparency (ZSD) ranged from 0.50 to 1,05 and from 0.46 to 1.0 m at the Central and Near Shore stations respectively, with high and low values corresponding to dry and rainy periods respectively. Mean vertical extinction coefficient varied temporally with higher values coincident with high algal biomass and abiogenic turbidity following rainy periods. The lake exhibited both superficial and deep-seated thermal stratifications, with ill-defined thermoclines on some occasions and never underwent complete mixing during the study period. Algal nutrients except nitrate-nitrogen showed temporal variations whose changes were inversely correlated with Chl a.The phytoplankton community of the lake, which consisted of five algal classess was dominated by cyanobacteria with Microcystis spp. as the most abundant and persistent taxa and with their contributions to the total abundance of the phytoplankton assemblage of the lake ranging from 58 to 99%. The zooplankton community was dominated by Calanoids and Rotifers with Lovenula africana and Brachionus spp.as the most numerically important taxa. Phytoplankton biomass measured as Chl a showed seasonal variations with maximum values during the rainy and post rainy months at both stations. Depth profile of photosynthesis showed a region of photoinhibition and condensed photosynthetic zone, a feature of some east African lakes. Light-saturated rates of gross photosynthesis (Amax) at the central station varied from a minimum of 410 to a maximum of 1630 mg O2 m-3 h- and with fairly strong and positive correlations with Chl a (R2=0.38, p=0.08), Soluble Reactive Phosphate, SRP (R2=0.46, p=0.07) and Light utilization efficiency, Φ (R2=0.61, p=0.02). Biomass specific rate at light-saturation exhibited unusually high values (29-91) and was positively and significantly correlated with SRP (R2=0.59, p=0.02), Areal rates varied from 0.89 to 3.88 g O2 m-2 h- 1 in association with biomass and Amax. The possible causes for the observed saptio-temporal variations in physico-chemical and biological features of the lake are discussed and suitable conservation strategies recommended.phytoplankton was based on short-term observations, which were not systematic. Wood and Talling (1988) have compiled the sporadic information on the dominant or most common species of phytoplankton reported in various limnological papers. The systematic and detailed taxonomic studies conducted on phytoplankton to date are those of Tsegaye Mihrete-Ab (1988), Elizabeth Kebede and Amha Belay (1994), Elizabeth Kebede (1996) and Elizabeth Kebede and Willén (1998). Also several studies (Talling et al., 1973; Amha Belay and Wood, 1984; Girma Tilahun, 1988; Brook Lemma, 1994; Taylor and Zinabu Gebre-Mariam 1989; Demeke Kifle and Amha Belay, 1990 and Eyasu Shumbulo, 2004; Girma Tilahun, 2006) have investigated the dynamics of phytoplankton in relation to some limnological aspects in Ethiopian lakes. Although the Bishoftu crater lakes have been subjects of many limnological investigations, some dating as far back to the early 1930's (Prosser et al., 1968), information on the temporal dynamics of the community structure and photosynthetic production of phytoplankton in relation to physico-chemical factors in Lake Bishoftu is non-existent. The early short-term comparative studies made on the Bishoftu lakes focused mainly on the assessment of general trends in physico-chemical limnological features. Even the few published reports on the phytoplankton biomass (Zinabu Gebre-Mariam, 1994; Wood and Talling,1988) and photosynthetic production (Talling et al., 1973) in the Bishoftu crater lakes were based on short-term observations although it was indicated that phytoplankton of tropical waters exhibit temporal changes in their species composition, biomass and primary production (Talling,1986). In Lake Bishoftu, some-short term studies have been reported on bathymetry, stratification, some chemical and morphometric aspects by expeditionary limnologists such as Baxter et al. (1965), Baxter and Wood (1965), and Wood and Talling (1988). These short-term studies were based on occasional sampling for the purpose of comparison among crater and tropical Rift Valley lakeComparative study with another soda lake, Lake Aranguade, on zooplankton structure and dynamics has been conducted by Afeworki Ghebrai (1992). Therefore, in comparison with other Debre-Zeit and Rift Valley lakes, someone can confidently talk of that Lake Bishoftu is not studied in phytoplankton aspect over extended periods. Zinabu Gebre-Mariam (1994), Brook Lemma (2002) and Zinabu Gebre-Mariam et al. (2002) have noted that the Ethiopian Rift Valley and crater lakes have been undergoing changes in their limnological features during the last two decades or so because of increased human interventions. The present study lake is no exception. Lake Bishoftu is surrounded by a fast growing town, Debre Zeit, and its shores are used for washing clothes, watering livestock and recreation and the like. Shoreline modifications made on almost all sides of the lake for various purposes (e.g. for the construction of resort hotels and residences in the catchments) introduce enormous amounts of particulate wastes, which form suspensions in the water column thereby reducing light penetration at least in the near-shore regions of the lake. The lake has also been serving as a major dumping site for domestic wastes (solid and liquid wastes) originating from households, hotels and small industrial operations, including a privately-owned tannery. These activities could lead to changes in the physico-chemical limnological features of the lake resulting in the disruption of the lake ecosystem, with consequent changes in the species composition and photosynthetic production of phytoplankton, which determine the pelagic food web structure and fish production in the lake. It is also possible that degradation of this aquatic ecosystem may go on unnoticed for a long time and eventually result in unexpected disastrous effects. The assessment of qualitative and/or quantitative changes taking place in this lake, therefore, necessitates the generation of basic information on the physical, chemical and biological aspects of this water body over an extended period of time.Thus, the purpose of this research project was to look into the temporal variation in the species composition, seasonal abundance and photosynthetic production of phytoplankton in relation to some physico-chemical variables in Lake BishoftuItem Effects of Water Hyacinth (Eichhornia Crassipes) on Water Quality and Composition and Abundance of Phyto- and Zooplankton in the Littoral Region of Koka Reservoir, Ethiopia(Addis Ababa University, 2019-05-05) Getnet, Habtamu; Kifle, Demeke (PhD); Fetahi, Tadesse (PhD)Invasion of aquatic habitats by non-native species is a global environmental challenge with serious ecological, social and economic consequences demanding urgent action. Water hyacinth, Eichhornia crassipes (Martius) Solms, is one of the world’s most rampant invasive aquatic plants recognized as one of the top 10 worst weeds in the world. Its appearance in Koka Reservoir was reported in 1965 and has become a threat to the aquatic ecosystem. Although several limnological studies have been made on the reservoir, the effects of water hyacinth on water quality and plankton have not been addressed. Samples were collected monthly from three weed-infested and three non-infested sites from March to July 2018 to assess its effect on water quality, plankton composition and abundance in the reservoir. Potential toxicity of water hyacinth extract was also investigated using white albino mice. During this investigation, the differences between weed-infested and non-infested sites in DO, NO3-N, NO2-N, SRP, TP, NH3, TSS, Turbidity, Silica and Secchi disk depth were significant (P<0.05), with lower values in the weed-infested sites except values of TSS, Silica and Turbidity higher in the weed infested sites. The phytoplankton community, which was constituted of 62 species, was dominated by Bacillariophyceae (mainly Aulacoseira granulata) followed by Cyanophyceae (Cylindrospermopsis spp., Microcystis aeruginosa, and Anabaena flos-aquae) and Chlorophyceae in both non-infested and weed-infested sites. The variations in the abundance of phytoplankton and zooplankton between the two sites were significant (p<0.05). The phytoplankton species Monorophidium griffithii and Gyrosigma obtusatum and the zooplankton taxa Lecane monostylahomata, Lecane leontita, Trichocerca djurellasejunctipes, Euchlanis menta, and Platyias quadricornis var. bervispinus were found only in the weed-infested sites. Significant differences in Shannon’s index (H'), species richness (d) and species evenness (j) of zooplankton and species richness (d) of phytoplankton were also observed between the two sites, with higher mean values in the non-infested sites than in the weed-infested sites (p<0.05). Rotifers, followed by Copepods and Cladocerans in the same order, were the most abundant at both sites. The relative density of Rotifers and Cladocerans was higher in the non-infested sites, while that of Copepods was higher next to Rotifesrs in the weed-infested sites. Results of the experimental test on the toxicity of water hyacinth on white albino mice showed unusual changes although the death of the treated mice was not observed suggesting the potential toxic effect of the weed on aquatic biota that would occur with an increase in dose and duration of administration. The existing infestation level of water hyacinth poses a significant effect on water quality, composition and abundance of phytoplankton and zooplankton. The current environmental conditions are favorable for the optimum growth of the weed and further proliferation of the weed and spread to new areas are possible worsening its adverse effect to the ecosystem. Thus, continuous monitoring and development of a sustainable management strategy and regulation of agricultural and urban wastes, have to be addressed.Item Field and Experimental Studies on Phytoplankton-Zooplankton Interaction in Lake Koka, With Particular References to Control of Microcystis Species(Addis Ababa University, 2018-07-05) Tialye, Aynalem; Kifle, Demeke (PhD); Fetahi, Tadesse (PhD)Blooms of Microcystis aeruginosa frequently occur in many eutrophic lakes in Ethiopia,however, there is very little experimental study on the relationship between Microcystis and Zooplankton from Ethiopian waters. The effects of different concentrations of toxic M. aeruginosa on two common freshwater zooplankton Cladoceran (Moina micrura)and Cyclopoid were investigated in laboratory experiments. The main purpose of this study was to examine if there is a difference in the development of tolerance to toxic Microcystis among two species of zooplankton copepoda (Cyclopoid) and a cladocera (Moina micrura )exposed to toxic Microcystis. We tested whether exposure to a toxic strain of cyanobacteria (Microcystis) affects survival, and growth, of a common herbivore, Cyclopoid and cladoceran(Moina micrura). In the experiments, cultures from the lakes will be test at five concentrations of toxic Microcystis aeruginosa: 0%, 20%, 50%, 80% and 100%.After 16 days, we compare the ability of these two populations to withstand the toxic Microcystis by assessing survivorship, and growth rate.Field study showed that Surface water temperatures of all sampling sites were within the range of variation reported for most tropical water bodies (23- 25ºC). Surface water DO(mg L-1), which was varied from 5.48 of the HEPP site to 6.99 of the MetoAleka shore site. Mean levels of nitratevaried between 0.11 HEPP and 0.224 mg L-1 Tannery, while those of ammonia ranged from 0.054 of the MetoAlekashore site to 0.033 Tannery mg L-1. Mean SRP (in mg L-1) 0.083 and 0.09 MetoAleka shore, TP, ranged from 0.254 mg L-1 Tannery of the site to 0.298 mg L-1 of the MetoAleka shore). The phytoplankton communities of all sampling sites were dominated, in terms abundance, by three alga groups, Cyanobacteria (blue-green algae), Bacillariophyceae (diatoms) and Chlorophyceae (green algae). Chlorophyceae was the most species-rich taxonomic group, followed by Cyanophyceae and Bacillariophyceae. The most abundance species were Microcystis sp, and Planktothrix cf.agardhii in Lake Koka. The zooplankton community in Lake Koka was dominated by the copepod which accounted for about 56% of total zooplankton abundance. From experimental result we get more survival rate for cladoceran treatment and low for copepod treatment. It can be suggested that biomanuplation controlling methods can be used to improve water quality in Lake Koka .Item Heavy Metal Levels in the Water and Sediment Samples of Dire and Aba-Samuel Reservoirs,Ethiopia(Addis Ababa University, 2019-05-05) Fenta, Abere; Fetahi, Tadesse (PhD); Kifle, Demeke (PhD)Dire is among the main sources of drinking water supply for Addis Ababa city while Aba-Samuel Reservoir is a multi-purpose reservoir for the nearby residents. However, the ever-intensifying anthropogenic activities in the catchment have increased the potential pollutants of these reservoirs. Of all the contaminants, heavy metals are non-degradable, can bio-magnify along the food chain and are probably toxic to humans and aquatic biota. Therefore, there is a need for continuous monitoring of the pollution levels in the reservoirs as the assessment provides evidence-based data to protect public health. The concentrations of selected heavy metals in water and sediment samples were collected and determined from three sites in each reservoir (Inlet; Site1-S1, Center; Site2-S2 and Outlet; Site3-S3) for three (3) consecutive months (April to June 2018). Physicochemical parameters (DO, temperature, EC, and pH) were measured at the established three sampling sites using portable Multimeter, while turbidometer was used to measure turbidity. The collected water and bottom sediment samples were analyzed by Inductively Coupled Plasma-Optical Emission Spectroscopy (ICP-OES) for selected heavy metals (Cu, Zn, Mn, Cr, Cd, Hg, Pb, and As). The data generated from the present study were statistically analyzed using Analysis of Variance (ANOVA). Physicochemical parameters except for temperature in Aba-Samuel Reservoir varied spatially although the differences in their levels among sampling sites were not significant (p>0.05). Among the physicochemical parameters measured in the field, only turbidity surpassed the acceptable limit set for drinking water by different organizations. The mean concentrations of heavy metals in bottom sediments (mg Kg-1) were higher than those in subsurface water samples (mg L-1). The highest concentrations of all metals measured in water and sediment samples were recorded for Mn in both Dire (0.236±0.014, 1098.90 ± 13.25) and Aba-Samuel (0.504±0.023, 1198.39± 6.85) reservoirs, respectively. Mean concentrations of all metals except Mn in water samples of Dire Reservoir were not significantly different among sampling sites (P>0.05), while the reverse was true for those of Aba-Samuel Reservoir. Some heavy metals in sediment samples of both reservoirs (e.g. Mn, Cr, and Pb) showed significant variations (P<0.05) among sampling sites while Zn showed spatial variations, which were not significant (P>0.05). The mean concentrations of heavy metals in water samples were all below the guideline values set by WHO (2008) and USEPA (2011) with the exception of Mn in both Reservoirs and Cd in Aba-Samuel Reservoir. Concentrations of Zn, Mn, Cr, and Cd in sediment samples are, however, above the respective reference values (ISQG, 2002; USEPA, 2010), while those of Pb and Cu were below the respective reference values (ISQG, 2002; USEPA, 2010) in both reservoirs. The results of the present study signify the importance of anthropogenic loading of pollutants and serve as an early signal for the need to take a timely measure to prevent further degradation of the reservoirs. Because the reservoirs are shallow and polymictic, the high concentrations of heavy metals in the sediment can lead to their increased levels in the water column thereby affecting public health and aquatic biota. Therefore, strategies of controlling point and non-point sources located all over the catchment areas should be developed to ensure better protection of the reservoirs, public health, and aquatic and terrestrial life.Item Key Drivers of Water Quality in Dire and Legedadi Reservoirs, Ethiopia(Addis Ababa University, 2019-06-06) Tilahun, Helnata; Kifle, Demeke (PhD); Fetahi, Tadesse (PhD)Dire and Legedadi reservoirs are the most important freshwater bodies used as surface water sources for the city of Addis Ababa. They are however, facing pollution problem owing to their establishment near fast-growing towns, industrial activities, and intensification of agriculture and the associated application of fertilizers within their catchment areas. Information on physicochemical and biological parameters of the reservoirs is required to manage their living resources and determine their suitability for drinking purpose. In this study, the seasonal and spatial dynamics of physicochemical and biological water quality parameters were therefore, investigated at monthly intervals during 5 months and 2 months of 2018 at three study Sites (Sites 1, 2 and 3) in Dire and Legedadi reservoirs, respectively. All physicochemical and biological parameters were determined with standard methods. Both reservoirs were characterized by unusually high turbidity (19.43-657NTU) throughout the study period mainly due to sediment input through runoff and wind-induced re-suspension of sediment particles. Water transparency of both study reservoirs was extremely low and showed seasonal variations with mean values ranging from 7.2 to 7.6cm (Dire Reservoir) and 4 to 6.5cm (Legedadi Reservoir). The values of water temperature recorded in the present study varied between 15.7 and 21oC. The pH in both study reservoirs was nearly alkaline (6.23-9.2) for most of the sampling months. Higher values were recorded for the concentration of most of the inorganic algal nutrients indicating the nutrient enrichment. Although TDS values were within the range that drinking water should have, high values were recorded throughout the study period. The unusually high turbidity (low water transparency) seems to be the major cause for the deterioration of the water quality in the reservoirs. The phytoplankton community was constituted by five taxa (Cyanophyceae, Chlorophyceae, Bacillariophyceae, Euglenophyceae, and Cryptophyceae) comprising 30 spp. with the dominance of Cyanophyceae including Microcystis aeruginosa, which are associated with public health risk. The zooplankton community comprised three major taxa (Rotifers, Copepods, and Cladocerans, consisting of 20 spp.) with copepod dominance. In general, the hypereutrophic condition in both reservoirs, which was suggested by the estimated TSI values, is indicative of the fact they are suffering from water quality deterioration associated primarily with the high turbidity and nutrient enrichment linked to human disturbance. In addition, the estimated WQI values placed Dire (57.6-73.65) and Legedadi (39.14 - 43.78) reservoirs under the categories of medium and bad water quality, respectively. The results of the present study seem to suggest the urgency of the need to develop workable strategies of restoration and protection from further degradation of the water quality of both reservoirs through catchment-based management since they together cover about 80% of the water demand of the capital and minimize the cost of water treatment and from the results of the present study a year round (seasonal) study is recommended in order to have a full information on the limnology of those reservoirs.Item Phytoplankton Production in Lake Arenguade (Hora-Hado), Ethiopia.(Addis Ababa University, 2010-06) Belachew, Misgina; Kifle, Demeke (PhD)Dynamics of Chl a biomass, abundance amd photosynthetic production of phytoplankton in relation to some phyico-chemical factors were studied in Lake Arenguade from December, 2008 to October, 2009. Water transparency in Lake Aranguade varied from 0.21 to 0.37 indicating the shallowness of the trophogenic zone owing to high turbidity, which seems to be largely of biological origin. Depth profiles of temperature showed the occurrence of a superficial type of thermal stratification which is created by solar heating and destroyed by nocturnal cooling although oxygen depth profiles determined on two days seem to sugggsest the formation of stable and deep-seated thermal stratification at times. Total Alkalinity of the lake ranged from 33 to 50.6 while pH varied from 9.62 to 9.84. SRP, nitrate and silica varied temporally from about 702 to 2123 μg L- , 1, 4.1 to 78 μg L-1 and 3.5 to 37.3 mg L-1, respectively. The phytoplankton community of Lake Arenguade was co-dominated by two species of blue-green anlgae, Spirulina platensis (Arthospira fusiformsi) and Anabaenopsis elenkinii, chl a biomass of phytoplankton varied temporally ranging from 41.7 to 271 mg L-1 and with peaks coinciding with those of phosphate and silicate and low levels of nitrate. The depthdistribution of gross photosynthesis per unite water volume (A, mg C m-3 h-1) exhibited the typical pattern for phytoplankton with maximum production rates at depths below the surface on most sampling dates.The light-saturated rate of gross photosynthesis (Amax), which ranged from 76.14 to 650 mg C (243.64–2080 mg O2) m-3 h-1. was positively but modestly (r=0.53, r2=0.28 at p=0.061 ) correlated with Chl a biomass. Biomassspecific rates at light-saturation (φmax, photosynthetic capacity) ranged from 2.3 to 13.2 mg O2 (mg Chl a)-1 h-1 with most values between 8 and 11 mg O2 (mg Chl a)-1 h-1. Hourly integral rates of photosynthesis (ΣA) ranged from 0.13 to 1.67 g O2 m-2 h-1. The seasonal peaks of hourly integral rates were associated with peaks of chlorophyll a concentration and light-saturated rate of gross photosynthesis (Amax). The correlations between hourly integral rates and chlorophyll a concentration (r=0.53, r2=0.28 at p=0.06 and Amax (r = 0.78, r2=0.62 at p=0.0014), were positive and strong. The causal relationship between biological parameters and physico-chemical variables are examined and discussedItem Seasonal Studies on Phytoplankton In Relation to Some Biological and Physico-Chemical Factors in Lake Hora-Kilole, Ethiopia(Addis Ababa University, 2008-07) Abate, Rediat; Kifle, Demeke (PhD)The temporal dynamics of plankton, benthic macroinvertebrates and physico-chemical variables were studied at a central station in Lake Hora-Kilole from August, 2007 to May, 2008. The lake remained small and shallow and consequently underwent complete mixing throughout the study period. Secchi depth ranged from 0.15 m to 0.78 m with high values coinciding with lower wind speed. Vertical extinction coefficient varied temporally (2.39-10.23 ln units m-1) with high values coinciding with relatively low algal biomass and high abiogenic turbidity associated with wind-induced mixing. SRP and TP varied from 0.33 to 3.5 and 2.13 to 6.15 μg L-1 respectively. The concentration of NO3 + NO2-N (in μg L-1) ranged from 17 to 303 while that of NH4++NH3–N varied from 1.7 to 49.09 μg L-1. Molybdate reactive silica (in mg L-1) ranged from 10.4 to 69.7. The phytoplankton community was composed primarily of green algae, euglenoids, diatoms, dinoflagellates and cyanobacteria with the overwhelming dominance of dinoflagellates and Cyanobacteria corresponding to the seasonal peaks of Chl a biomass of phytoplankton. The most dominant species of Dinoflagellates and Cyanobacteria were Peridinium gatunense and Anabaena cf. agardhii and cylindrospermopsis curvispora respectively. Zooplankton abundance peaked in February, 2008 coincident with the largest peaks of phytoplankton biomass and abundance and with Thermocyclops decipiens, Brachionus sp. and Daphnia barbata as the most important taxa. Among the macroinvertebrates, chironomids and Lambriculidae-oligochaete were dominant during the dry period. Total phytoplankton biomass showed seasonal variations (≈36 to 148 μg L-1) with large peaks in October, 2007(≈148 μg L-1) and February, 2008 (≈147 μg L-1) and the seasonal minimum (≈ 36 μg L-1) in January, 2008. Among the three size-groups of phytoplankton, the netplankton (> 20 μm fraction) was the most important contributor to the total phytoplankton biomass with its biomass and percentage contributions to total phytoplankton biomass ranging from 13.21 mg m-3 and 32 % to 132.06 mg m-3 and 95 %, respectively. The percentage contributions of nanoplankton and picoplankton varied from about 0 to 64% and from 4 to 28 %, respectively. Depth profiles of gross photosynthesis were of typical pattern for phytoplankton without surface photoinhibition during the major rainy period. Light-saturated rate of gross photosynthesis (Amax) varied from 370 to 3843 mg O2 (≈111.5– 1199 mg C) m-3 h-1 with the maximum value corresponding to the seasonal maximum of phytoplankton biomass. Biomass-specific rate of gross photosynthesis at light-saturation varied from about 6 to 33 with positive and moderate correlation (r=0.632, r2=0.40 at p=0.0496) with SRP. Hourly integral rate of gross photosynthesis, (ΣA), which was positively and strongly correlated with Amax (r= 0.885, r2=0.7895 at P = 0.0006) and Zeu (r=0.7849, r2=0.616 at p=0.0072), ranged from 0.21 to 6 g O2 (≈ 0.065 - 1.87 g C) m-2 h-1. The marked temporal variations in phytoplankton parameters are discussed in relation to physicochemical and biological variables.and the general knowledge of some biological characteristics of the species (Garcia et al., 1989). Limnology in the tropics has only recently developed past the stage of exploration, but the need of limnological knowledge is, as pressing at tropical latitudes as in the temperate (Melack, 1996; Talling and Lemoalle, 1998, Lewis, 2000). Despite the perturbation by humans, vast number of lakes of varied size and shape are found in most tropical regions. They are often inhabited by densely populated biota and have been the subject of some of the most scientifically informative studies of tropical aquatic ecosystems (Talling, 2001). In Africa, the first assessment of phytoplankton seasonality stemmed from collections made in 1899 by the Fullenborn expedition to Lake Nyassa, and later to Lake Malawi (Talling, 1986). Extensive efforts were made after 1950, especially in East and Central Africa (Talling, 1986). Despite their tropical location, African lakes exhibit considerable seasonality related to alternations of warm, wet, cooler and dry seasons. Although numerous studies have been made on the species composition and photosynthetic production of phytoplankton in various East African lakes (Talling and Lemoalle, 1998), relatively little has been done on this aspect in Ethiopian lakes. Ethiopia is rich in both natural water bodies such as rivers and lakes and man-made lakes (reservoirs) compared to other east African countries. Ethiopia also possesses many great crater lakes (Prosser et al., 1968), among these are the Bishoftu crater lakes, which form an extensive series of volcanic explosion craters in the vicinity of the city of Bishoftu (Debrezeit). The Bishoftu crater lakes are grouped among the most scientifically known lakes of Ethiopia until recently (Zinabu Gebre-Mariam, 1994). Volcanic crater lakes include lakes located in crates formed after eruption and they have small surface area and steep crater wall (Hutchinson, 1957). We have some scientific information on the Bishoftu crater lakes dating as far back as the early 1930`s and 1940`s (Omer-Cooper, 1930; Vatova, 1940; Loffredo and Maldura, 1941; Cannicci and Almacia, 1947, cited in Prosser et al., 1968). In the early 60`s, different aspects of these lakes were studied (Baxter et al.,1965; Baxter and wood, 1968; Prosser et al., 1968; Talling et al., 1973; Wood et al., 1976, 1976, 1984; Wood and Talling, 1988). It is these investigations which tempted Zinabu Gebre-Mariam (1994) to describe the Bishoftu crater lakes as being among the most studied lakes of Ethiopia. There is, however, scanty scientific information on several aspects of these lakes, particularly on some biological aspects. Lakes throughout the temperate and tropical latitude have been drastically altered as a result of the burden they carry when there is an increase in population density, economic growth, and change in land cover (Lewis, 2000). It is also known that climatic change especially rainfall, have a prominent effect on the limnology of a lake, resulting in changes in different parameters of a lake. Human interventions are the main cause of lake deterioration and it has various consequences. Human interferences are frequently reflected as changes in the trophic status of the lake, volume of the water, and consequent ecological changes. This is a phenomenon observed throughout the world, with some lakes changing from oligotrophic to eutrophic through mesotrophic or the reverse could happen. Increase or decease in the biomass of plankton and level of nutrients and alteration in the underwater climate are some of the symptoms of eutrophicaton and/or oligotrophication. Thus, the trophic status of a lake can be determined from different physico-chemical and biological parameters. Euphotic depth, concentration of a limiting nutrient, phytoplankton biomass, primary productivity, and phytoplankton abundance are some of the basic and direct indicators of the trophic status of Lake. One can also look at the abundance and biomass of consumers (Zooplankton and fishes) to predict tropic status. These, the same parameters can be used to determine long term changes of lakes, and for comparison of two or more lakes (Brook Lemma, 2002). The assessment of these physico-chemical and biological parameters is, therefore, crucial to evaluate the ecological health of aquatic ecosystems, optimize their exploitation, manage and conserve their resources. Most of the Ethiopian lakes including the Bishoftu crater lakes, which are in the vicinity of a fast-growing town surrounded by agricultural lands, are subjected to shoreline modification, waste disposal, and other practices associated with population growth (Zinabu Gebre-Mariam, 1998; Zinabu Gebre-Maraim, et al., 2002). Furthermore, many water bodies (predominantly rivers and lakes) in Ethiopia have been physically degraded or altered seriously by human manipulation (e.g. L. Hora-Kilole) and habitats have consequently been lost (e.g. L Haramaya) (Brook Lemma, 2002). Human-induced changes of lakes in Ethiopia are exemplified by the eutrophication of Lake Hayk (Elizabeth Kebede et al., 1992), shrinkage of Lake Alemaya (Brook Lemma, 1994; 2002) and drastic changes in the water chemistry and species composition and productivity of phytoplankton in Lake Hora-Kilole (Brook Lemma, 1994; 2002). Lake Hayk has changed greatly in its phytoplankton biomass and transparency (Elizabeth Kebede et al., 1992). This was possible because of the introduction of planktivorous fish which freed the phytoplankton from grazers’ control. The lake was stocked with tilapia species from a crater lake, probably Lake Hora in 1978 by the Fisheries Department, Ministry of Agriculture, to provide food, and harvest by a newly established fish gillnet. The commercial fishery of the lake increased to 200 tones per year (84Kg per hectare) (Elizabeth Kebede et al., 1992). Lake Alemaya has been used for irrigation, animal watering and household consumption and consequently dramatic changes occurred in its volume has occurred (Brook Lemma, 1994; 2002). Lake Hora-Kilole was once grouped among the unique saline lakes of Africa, such as Arenguade, Chitu, Abijata and Shalla in Ethiopia and Nakuru in Keneya (Prosser et al., 1968; Talling et al., 1973; Vareschi, 1982; Wood et al., 1984; Elizabeth Kebede et al., 1986; Wood and Talling 1988; Green 1986; 1993; Tudorancea et al., 1999). This lake was also known for its superabundance of Spirulina spp. assemblage and avifauna. In 1989, the Ministry of Agriculture (MOA), Addis Ababa, in an attempt to use the lake as a reservoir to gravitationally irrigate the southern and eastern low-lying plains, diverted River Mojo into Hora-Kilole resulting in the complete transformation of the lake ecology (Brook Lemma, 1994; 2002). After the diversion of the river, few investigations have tried to show ecological changes in the Lake (Brook lemma, 1994; 2002, Zinabu Gebre-Mariam, 1994; Zinabu Gebre-Mariam et al., 2002). Diversion of R. Mojo into Hora-Kilole has caused substantial changes in the morphometric, biological and physicochemical characteristics of the lake. So the aim of this study is to complement and update the physico-chemical and biological data generated for the lake in previous studies, which may help us show the seasonal and long-term changes that have occurred in the lake.Item Some Biotic and Abiotic Factors Affect Phytoplankton Functional Groups in Lake Hawassa, Ethiopia(Addis Ababa University, 2020-07-07) Beyene, Getacher; Kifle, Demeke (PhD); Fetahi, Tadesse (PhD)The water quality of Lake Hawassa has been deteriorated due to high influent load from various sources, including effluents of a hospital, industries, hotels, and agricultural runoff, which can induce changes in phytoplankton functional groups (FGs). The functional association of algae can also be affected by the dominant zooplankton and macrophytes coverage. FGs are groups of phytoplankton species with similar ecological requirements. The FGs approach has greater effectiveness than the taxonomic method in detecting the changes in phytoplankton assemblages in relation to the predominant environmental stressors. No previous study has however been conducted on the FGs in the lake. It was hypothesized that the introduction of pollutants through the various influents of the lake and the composition and abundance of the major zooplankton groups, and the presence of Echichloa pyramidalis (emergent macrophyte) influence the FGs. The main objective of this study was, therefore, to document scientific information on the variations of phytoplankton FGs in relation to these ecological factors in Lake Hawassa, Ethiopia. Sample collection and insitu measurements of physico-chemical parameters were made monthly (April to August in 2019) from four sites. Data analyses were performed using SPSS version 20 and CANOCO version 4.5. A total of 130 species of phytoplankton were identified and classified into 18 trait-based functional groups (RFGs) and 6 morphology-based functional groups (MBFGs). SN, M, P, J, and LO were the most dominant FGs contributing for 91.17% of the total fresh weight biomass of the RFGs. III, IV, V, VI and VII, which accounted 99.0035% of the total fresh weight biomass, were the most conspicuous MBFGs. RDA analysis indicated that the RFGs SN, Lo, M, F, N, J, P, MP and D and the MBFGs III, V, VII, IV and VII were correlated significantly with electrical conductivity, DO, pH, TSS, turbidity, Secchi depth and total phosphorus (P ≤ 0.004) revealing the overriding importance of these parameters in influencing the variation of the phytoplankton FGs in Lake Hawassa. The potentially toxigenic FGs were dominant at the Macrophyte zone due to their preference for shading and water column stability. Rotifers and cyclopoid copepods were the dominant zooplankton taxa with no significant impact on the FGs. The results of this study supported our hypothesis that the biotic (the macrophyte Echinochloa pyramidalis) and the human-induced abiotic (the influents associated) factors have significant impact on the phytoplankton FGs. But, further research is mandatory to better understand the underlying mechanisms governing their interactions. The current study can have practical importance to efforts directed towards improving the water quality of the lake and may also serve as base-line information for further studies.Item Some Biotic and Abiotic Factors Affect Phytoplankton Functional Groups in Lake Hawassa, Ethiopia(Addis Ababa University, 7/7/2020) Beyene, Getacher; Kifle, Demeke (PhD); Fetahi, Tadesse (PhD)The water quality of Lake Hawassa has been deteriorated due to high influent load from various sources, including effluents of a hospital, industries, hotels, and agricultural runoff, which can induce changes in phytoplankton functional groups (FGs). The functional association of algae can also be affected by the dominant zooplankton and macrophytes coverage. FGs are groups of phytoplankton species with similar ecological requirements. The FGs approach has greater effectiveness than the taxonomic method in detecting the changes in phytoplankton assemblages in relation to the predominant environmental stressors. No previous study has however been conducted on the FGs in the lake. It was hypothesized that the introduction of pollutants through the various influents of the lake and the composition and abundance of the major zooplankton groups, and the presence of Echichloa pyramidalis (emergent macrophyte) influence the FGs. The main objective of this study was, therefore, to document scientific information on the variations of phytoplankton FGs in relation to these ecological factors in Lake Hawassa, Ethiopia. Sample collection and insitu measurements of physico-chemical parameters were made monthly (April to August in 2019) from four sites. Data analyses were performed using SPSS version 20 and CANOCO version 4.5. A total of 130 species of phytoplankton were identified and classified into 18 trait-based functional groups (RFGs) and 6 morphology-based functional groups (MBFGs). SN, M, P, J, and LO were the most dominant FGs contributing for 91.17% of the total fresh weight biomass of the RFGs. III, IV, V, VI and VII, which accounted 99.0035% of the total fresh weight biomass, were the most conspicuous MBFGs. RDA analysis indicated that the RFGs SN, Lo, M, F, N, J, P, MP and D and the MBFGs III, V, VII, IV and VII were correlated significantly with electrical conductivity, DO, pH, TSS, turbidity, Secchi depth and total phosphorus (P ≤ 0.004) revealing the overriding importance of these parameters in influencing the variation of the phytoplankton FGs in Lake Hawassa. The potentially toxigenic FGs were dominant at the Macrophyte zone due to their preference for shading and water column stability. Rotifers and cyclopoid copepods were the dominant zooplankton taxa with no significant impact on the FGs. The results of this study supported our hypothesis that the biotic (the macrophyte Echinochloa pyramidalis) and the human-induced abiotic (the influents associated) factors have significant impact on the phytoplankton FGs. But, further research is mandatory to better understand the underlying mechanisms governing their interactions. The current study can have practical importance to efforts directed towards improving the water quality of the lake and may also serve as base-line information for further studies.Item Temporal Changes in the Community Structure and Kotosynthetic Production of Phytoplankton in Lake Babogaya, Ethiopia(Addis Ababa University, 2006-07) Major, Lesbimebet; Kifle, Demeke (PhD)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.Item Temporal Dynamics of Biomass and Primary Production of Phytoplankton In Relation to Some Phsico-Chemical Factors In Lake Koriftu, Ethiopia(Addis Ababa University, 2007-07) Dessalegn, Zelalem; Kifle, Demeke (PhD)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.Item Temporal Dynamics of the species composition and Size fractionated Biomass of Phytoplankton in Lake Kuriftu, Ethiopia(2016) Mohammed, Nebeyu; Kifle, Demeke (PhD)The temporal dynamics of phytoplankton and physic-chemical variables were studied at a central station of Lake Kuriftu from December, 2008 to November, 2009. The lake is shallow and as a result undergone complete mixing throughout the study period. Secchi depth ranged from 0.21 m to 0.6 m. The Lake’s transparency (ZSD) was always less than 0.6 m with smaller values coincident with high phytoplankton biomass even though there is weak correlation b/n phytoplankton biomass and ZSD. The chemistry of the lake was basically similar to the dilute East African lake waters, with maximum pH and total alkalinity values of 9.09 and 4.1 meq/l respectively. Nitrate concentration (μg L-1) ranged from a minimum of 9.33 in November, 2009 to 65.45 in April, 2009. Soluble reactive phosphate- phosphorus (SRP, in μg L-1) varied from a minimum value of 14.65 in January, 2009 and May, 2009 to a maximum of 402.57 in August, 2009. Dissolved silica (Molybdate-reactive silica, SRSi in mg L-1) ranged from 3.051 in December, 2008 to 97.92 in September, 2009. The phytoplankton community which was dominated by Cyanobacteria is 2nd in diversity to chlorophycea which covers 25 species of the 50 species. Cylinderospermopsis Africana was the most dominant species throughout the study period.The diversity index was narrow ranging from 1.24 -6.42 bits/individual. Among the three size-group of phytoplankton, the nanoplankton (2-20 μm) was the most important contributor to the total phytoplankton biomass with its biomass and percentage contributions to the total phytoplankton biomass ranging from 15.44 μg L-1and 51.93 % to 19.74μg L-1 and 73.84 % respectively. The Chl a biomass and percentage contribution to total phytoplankton biomass of the Netplankton and Picoplankton varied from 1.94 to 6.73 and 6.53 % to 13.87% and 4.68 to 14.63 and 17.5% to 41.54 % respectively. The factors responsible for the observed spatiotemporal variations in the physical,chemical and biological features of the lake are discussed. Key words: Lake Kuriftu, Size fractionated Biomass, Phytoplankton, Temporal Variation.Item Water Quality and Phytoplankton Dynamics in Geffersa Reservoir/ Ethiopia(Addis Ababa University, 2010-06) Ebisa, Nigatu; Kifle, Demeke (PhD)Dynamics of phytoplankton and physico-chemical parameters of water quality were studied in Geffersa Reservoir from October, 2009 to June, 2010 using samples collected at bi-weekly intervals. Secchi depth (vertical visibility) varied from a minimum of 0.20 of the minor rainy season to a maximum of 0.66m during the dry period. Turbidity, which fluctuated between 7.2 and 189 NTU, exhibited a seasonal pattern, which was more or less similar to that of phytoplankton biomass measured as Chl a (r= 0.649, r2= 0.415 at p= 0.0070). The concentrations of NO3-N, NH3 + NH4+- N and Soluble Reactive Phosphate (SRP) varied from 10.0 to 300, 146 to 866 and 29 to 201 μg L-1 respectively while Molybdate-reactive silica ranged from 2.5 to 13.4 m L- 1. Turbidity, TDS, and other chemical parameters were found to be far below the upper permissible limits for drinking water supply sources. The phytoplankton community whose species diversity was found to be low was primarily constituted by green algae, blue-green algae and diatoms, the contributions of the species-rich green algae ranging from 1 to 95 % and with major species belonging to the genera Crucigenia, Kirchneriella and Ankistrodesmus. The second and third most abundant algal groups were the blue-green algae and diatoms, which were dominated by two species of Microcystis, M. aeruginosa and M. panniformis. and by a species of the filamentous genus Melosira, M. agassii, followed by Fragilaria capucina and Rhopalodia gibberulla. Among the flagellate groups, dinoflagellates were the most important, with Peridinium cinctum and P. bipes as the quantitatively most important species. Among the cryptomonads, Cryptomonas marsonii and C. ovata were found in large numbers, Chl a biomass of phytoplankton averaged 12.41 μg L-1 and varied from a minimum of 2.29 μg L-1 to a maximum of 40.67 μg L-1 with its fluctuations being correlated more with ammonia +ammonim (r =0.662, r2 = 0.44 at p=0.0045) than with nitrate (r=-0.4093, r2= 0.1675 at p= 0.1028) or phosphate (r= 0.435, r2=0.289 at p= 0.0800). Rotifers were the most abundant and species-rich zooplankton group with mean percentage contributions of 66.82 while the contributions from copepods and cladocerans were 24.51% and 8.67% of the total abundance of the zooplankton respectively. The causal relationships among physicochemical and biological variables are discussed and recommendations made.