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A review of the impacts of invasive aquatic weeds on the bio- diversity of some tropical water bodies with special reference to Lake Victoria (Kenya)
(Biodiversity, 0020-12-30) Aloo, Peninah; Ojwang, William; Omondi, Reuben; Njiru, James Murithi; Oyugi, Dalmas
Aquatic weeds may be defined as troublesome or unsightly plants growing in abundance inaquatic situations where they are not wanted. These plants are either adapted to continuoussupplies of water or are at least tolerant to waterlogged soil conditions for substantial periodsof time. The wide range of adaptation to varying amounts of water, and the impossibility ofsharply distinguishing between aquatic and terrestrial environments, makes it difficult toprecisely define an aquatic plant. The menace of water weeds is reaching alarming proportions in many parts of the world, especially in tropical water bodies where they have led toserious ecological and economic losses. Lake Victoria, Kenya, which is the largest freshwaterbody in the tropics, has undergone serious ecological changes including over-exploitationof its fishery resources, degradation of the catchment area, introduction of exotic fish speciesand invasion by the water hyacinth, Eichhornia crassipes (Mart.) Solms (Pontederiaceae),among others. The presence of the weed in the lake has led to many problems includingblockage of water pumps, reduced fishing activities and increase in water borne diseasessuch as schistosomiasis. Positively, aquatic weeds constitute a free crop of great potentialvalue; they are a highly productive crop that requires no tillage, fertilizer, seed, or cultivation.Moreover, these plants have the potential for exploitation as animal feed, human food, sourceof food to some aquatic organisms, soil additives, fuel production, wastewater treatment,source of raw materials and habitat to many organisms. This paper reviews the effects ofaquatic weeds in aquatic systems with examples from some selected waterbodies and specialreference to Lake Victoria.
A review of the changes in phytoplankton community structure and ecology in lake naivasha, kenya
(Academic Journals, 1970-01-01) Argwings Owino Omondi, Steve Opiyo Balaka, George Ogendi Mokua, James Onchieku Mokua, Steve Oduor Omondi
Phytoplankton community structure plays a vital role in freshwater ecosystems. Besides the provision of dissolved oxygen through photosynthesis, they also form an important diet for several fish and zooplankton species. Plankton are also used as biological indicators of water quality. The objective of this paper is to provide a comprehensive review on the changes in phytoplankton community structure and their ecological functional roles. Phytoplankton are the primary producers in Lake Ecosystem. The diversity, distribution, and abundance of phytoplankton are influenced by both abiotic and biotic factors. Lake Naivasha has undergone drastic ecological changes due to the growth in human population, horticultural and floricultural developments and changes in its fisheries. Lake Naivasha is surrounded by horticultural farms that are greatly influencing its ecosystem health and the major fish species in the lake are of introduced species. These anthropogenic activities together with hydrological changes are expected to play a role in the changes in phytoplankton community structure. Previous investigations indicate that there are more than 143 species of phytoplankton and seasonal shift in phytoplankton dominance overtime between Chlorophyta, Bacillariophyta, and Cyanophyta. Due to various limnological, hydrological, and ecological changes being witnessed in the Lake, there is need for the monitoring of phytoplankton community structure. Such information would be useful in the Lakeâ€™s management and conservation.
Generalized characteristics of intense rainfall and peak discharges in Athi basin, Kenya
(JSHWR Committee on Editorial and Publication Affairs, 1995) Nyadawa, Maurice O.; Kobatake, Shigeki; Ezaki, Kazihiro
Presented in this paper is a study clarifying any distinctions or similarities in trends of extreme value statistics of rainfall and discharges recorded at stations sampled all over a basin traversing three distinct climatic zones in Kenya. It is found that in Athi basin, difference in seasonal rainfall pattern affect general characteristics of intense rainfall more significantly than spatial variation of mean annual rainfall. Survey of flood potential of the basin revealed zones which are considered hydrologically homogeneous and heterogeneous cases.
Estimating Transmission Losses in the Main Channel of River Tana, Kenya
(J-Stage, 1997) Nyadawa, Maurice O.; Kobatake, Shigeki; Ezaki, Kazuhiro
This study has presented correlation equations thought to define channel loss in River Tana in Kenya. Modified Tank Model is used to transfer runoff information from gaged basins to ungaged ones in the study area. The study has revealed that channel loss has two step functions corresponding to flow rates below 800m3/s and larger values.
Importance of Indeginous Macrophytes in Control of Water Hyacinth in the Nyanza Gulf of Lake Victoria, Kenya.
(Aquadocs, 2000) Omondi, Reuben; Gichuki, John
Observation of macrophytes dynamics in the Nyanza gulf of Lake Victoria is ongoing since the early 1990s. A checklist of the macrophytes and their distribution in the study area is provided. Occurrence of macrophytes before and after the invasion of water hyacinth is highlighted. The dynamics of water hyacinth, control measures employed for its control and macrophyte succession are also mentioned.
Management and Ecology of Lake and Reservoir Fisheries | Wiley
(Wiley, 2002-02) G.Cowx, Ian
In this comprehensive edited book, international experts in fisheries management and ecology review and appraise the status of lake and reservoir fisheries, assessment of fisheries yields, trophic ecology, rehabilitation and conservation, including a special section on African lakes where so much information of huge relevance to fisheries managers is now available . Contributions from around the world. Carefully edited by internationally respected editor. Has been generated from acclaimed HIFI Symposium.
Effects of Zinc, Lead and Copper Concentration Levels on the Distribution of Macro Invertebrates: A case Study of River Sosian, Eldoret Town, Kenya
(journal of the kenya chemical society, 2004-08) Osano, Aloys; L.L., Cheruiyot
The relationship between zinc and copper concentration levels and the distribution of benthic macro-invertebrates in river Sosiani, Eldoret has been investigated. Atomic Absorption Spectrophotometry (AAS) and the Dip-net method have established the concentration of zinc and copper and the number of macro-invertebrates respectively. The study showed that the concentration of both copper and zinc were higher than the threshold levels and that the macro-invertebrate species were fewer in the more polluted regions of the river. Thus, zinc and copper concentration levels play a role in the distribution of macro-invertebrates.
Macrophytes of Lake Victoria and succession after invasion of Water Hyacinth
(AQUA DOCS, 2006) Omondi, Reuben; Kusewa, Mwende
The distribution of Lake Victoria macrophytes is described. Succession of macrophytes in the lake became more dramatic and dynamic after invasion of water hyacinth. The weed pushes and smothers other free-floating macrophytes like Pistia stratiotes. It then provides substrates for the emergent Vossia cuspidata, which later reduces its population by competition for light and nutrients. The noxious weed is believed to have led to extinction of Azolla nilotica in the lake.
Systematics and distribution of zooplankton in Lake Victoria basin, Kenya
(AQUA DOCS, 2006-01) Mutune, Masai; Omondi, Reuben; Owili, Monica
Zooplankton samples were collected, using a 60µm nansen net, from Lake Victoria and adjacent water bodies with emphasis being placed on the different habitats within the ecosystems. A total of 116 species were identified, 63 rotifers, 24 cladocerans and 29 copepods. A number of these were new records for the zooplankton fauna for the country.
Groundwater overdraft vulnerability and environmental impact assessment in Arusha
(Springer, 2006-07-11) Ong’or, Basil T. I.; Cang, Shu Long
A simple approach is proposed for identifying areas vulnerable to groundwater overdraft. The methodology utilizes GIS techniques to analyze and evaluate controlling factors in areas with little data. The proposed methodology was applied in Arusha. Water demand in Arusha Municipality and its environs has increased to about 5.3% annually since 1999. Groundwater levels have declined. The aquifer hydrogeological variables were evaluated for impact to potential groundwater overdraft by overlay and index techniques. The spatial distribution of overdraft vulnerability was discussed. The northwestern part of Arusha is the most vulnerable to overdraft and possible serious environmental impacts. The Loruvani area has the most potential for aquifer development due to its permeability, high recharge rate, massive aquifer thickness and low drawdown.
Environmental impact assessment of risk associated with groundwater overdraft remediation in cone of depression, Jining, China
(Springer, 2007-01-12) Ong'or, Basil; Shu, Long-cang; Liu, Pei-Gui
In this paper, a simple scenario and probabilistic approach is used to assess the potential groundwater risk due to proposedoverdraft remedial actions in cone of depression, Jining City, China. Focusing on the concentrations of Chloride ions (Cl−) and total hardness (TH), the impact of artificial recharge and reduced pumping on groundwater quality and quantity is analysedby using the three-dimensional finite difference groundwater flow and transport model, Visual MODFLOW, to simulate groundwaterflow and transport within the study area based on scenarios, and utilizes SURFER software to map risk levels. Although 5,10 or 15% reduced pumping with artificial recharge leads to more decrease in Cl− and TH concentrations than the 25%, less volume increase is achieved for the remediation of land subsidence and other environmentalproblems in the cone of depression. The Cl− concentrations in recovered groundwater are within the desired concentration of 200mg/l; however, TH in some cases are abovethe maximum permissible limit of 500mg/l, with an exceedence probability of about 0.67 for recharge and recharge with reducedpumping at 25%. The presence of fractures and hydrogeological complexity greatly determines impacts of remediation, and the22% reduced pumping with artificial recharge offers an optimum strategy for overdraft remediation in the Jining cone of depression.
Influences of land use/cover on water quality in the upper and middle reaches of River Njoro, Kenya
(Blackwell Publishing Asia Pty Ltd, 2007-04-20) Muchiri, Mucai; Shivoga, William A.; Kibichi, Samuel; Odanga, Jethro; Miller, Scott N.; Baldyga, Tracy J.; Enanga, Eric M.; Gichaba, Maina C.
Data from 10 sampling sites along the River Njoro are used to examine the contribution of nutrients from upstream land uses draining each of the sampling sites. The data also are used to assess whether both the proportion of land uses and the size of the subwatersheds account for the variability in water quality in the River Njoro watershed. Geographical Information System analysis was used to determine the spatial distribution of land-cover types and subwatersheds contributing run-off to the sampling sites in the River Njoro. Standard Digital Elevation Model-based routines were used to establish the watershed area contributing run-off to each sampling site. Water and sediment samples were collected for chemical analysis, and the nutrient levels were related to the upstream land-use types and the size of the subwatersheds. The mid-stream portion of the River Njoro (near Egerton University) accounts for the highest nutrient contributions. The percentage contribution is magnified by additions from industrial, human settlements and agricultural land uses around the University. There is a significant decrease in nutrient levels downstream, however, indicating natural purification as the river flows through an area of large-scale farming with intense, well-preserved riparian and in-stream vegetation. Steep slopes of the land upstream of Egerton University enhance erosion and nutrient losses from those subwatersheds. Mixed small-scale agricultural and bare lands contribute over 55% of the phosphorus load to the upper and mid-reaches of the River Njoro. The size of the subwatershed accounts for about 53% of the variability in the soluble phosphorus in the river. The land-use subwatershed proportions are important for characterizing and modelling water quality in the River Njoro watershed. Upland land uses are as important as near-stream land uses. We suggest that conservation of intact riparian corridor along the river and its tributaries contributes significantly to natural purification processes and recovery of the ecological integrity of the River Njoro ecosystem
Spatial and temporal changes in the distribution of Rastrineobola argentea in Lake Victoria
(Taylor & Francis group, 2007-11-26) Tumwebaze, R.; Cowx, I.; Ridgway, S.; Getabu, A.; MacLennan, D. N.
Following recent changes in the ecosystem of Lake Victoria resulting from the introduction of Nile perch, Lates niloticus, in the 1960s, there is urgent need for information on which to formulate rational exploitation and management of the fisheries resources. This paper presents information on the biomass and distribution of dagaa, Rastrineobola argentea, the second most important commercial species in Lake Victoria. Data were collected during five acoustic surveys conducted between 1999 and 2001, using a Simrad EY500 echo–integrator with a 120 kHz split–beam transducer. Fish samples were collected using a frame trawl, bottom trawl and pelagic trawl, all lined with 5 mm mesh size netting. The mean total biomass of R. argentea in the lake was 476,902 ± 339,308 t at an average fish density of 7.3 ± 5.4 t km −2 in the sampled area. Potential yield was estimated at 581,584 ± 305,377 t (8.5 ± 4.4 t km −2 ). The majority of the biomass of R. argentea (an average of 68%) was distributed in waters of more than 40 m depth. The biomass of R. argentea increased progressively over the survey period, probably as a result of decreased predation pressure by Nile perch.
The role of the Yala swamp lakes in the conservation of Lake Victoria region haplochromine cichlids : Evidence from genetic and trophic ecology studies
(Wiley, 2008-05-04) Abila, Romulus; Salzburger, Walter; Ndonga, Millicent; Owiti, Dickson; Barluenga, Marta; Meyer, Axel
Lake Kanyaboli, an isolated satellite lake of Lake Victoria, has been suggested as a potential refugium for haplochromine cichlids that have gone extinct in the main basin of Lake Victoria. Mitochondrial DNA (mtDNA) molecular markers, as well as feeding ecology studies, were employed in this study to re-evaluate the evolutionary and ecological significance of six common Lake Kanyaboli haplochromines. The mtDNA marker revealed high genetic variability within four of the six haplochromine cichlids. Five haplotypes were discerned in Astatoreochromis alluaudi (n = 27), seven in Lipochromis maxillaris (n = 29), five in Astatotilapia nubila (n = 12) and 11 in the endangered Xystichromis phytophagus (n = 205). A haplotype genealogy suggests that Lake Kanyaboli harbours mtDNA haplotypes that could have been lost or not sampled in Lake Victoria, or could have arisen in situ. Lipochromis maxillaris appears to have undergone a recent demographic expansion. The pairwise FSTs indicated that only the comparison between X. phytophagus and A. nubila led to a non-significant FST value. All other comparisons were significant at the 0.01 level, indicating the genetic distinctiveness of the haplochromines in the satellite lake. This could suggest that the lake harbours 'pure' relict populations of the haplochromines and therefore that Lake Kanyaboli can be considered a 'genetic reservoir'. Gut content analysis of the six haplochromine species revealed that eight different food items were consumed. No single species fed exclusively on a single food item, but certain food items contributed higher proportions of the fish diet for each fish species. Resource partitioning therefore could be discerned within this haplochromine community. Thus, Lake Kanyaboli and similar satellite lakes provide an opportunity for conservation of both genetic and trophic diversity threatened by introduction of exotics in the Lake Victoria basin. Lake Kanyaboli should be recognized and conserved as important evolutionary significant units for Lake Victoria region haplochromine species.
Environmental impact assessment using FORM and groundwater system reliability concept: case study Jining, China
(Springer, 2008-08-01) Shu, Long; Liu, Pei-Gui; Ong'or, Basil
In this paper, fist-order reliability method (FORM) is used to evaluate the impacts of uncertainties posed by traditionaldeterministic models on the environment in Jining, China. Because of groundwater contamination in shallow aquifer, and anincrease in water demand, the new wells target the confined aquifer with constant pumping rate of 5,000m3/d. Using Theis equation, the groundwater drawdown is analyzed to determine whether the confined aquifer will be contaminated.Although the piezometric level is higher than the phreatic level by 11.0m, the risk of drawdown is still 19.49% when thepumping rate of 5,000m3/d is maintained for 2years. The deterministic model indicates a drawdown of 8.94m which is lower than the maximum tolerancedrawdown of 11.0m. The sensitivity and uncertainty analysis reveal that the model result is more sensitive to transmissivitythan specific yield, while the reliability analysis offers significant information for the decision makers. This approachexposes and minimizes the risk of undesirable consequences such as groundwater contamination.
Groundwater overdraft and the impact of artificial recharge on groundwater quality in a cone of depression, Jining, China
(taylor and francis, 2009-12-03) Ong'or, Basil T. I.; Cang, Shu Long
Groundwater overdraft has led to cone of depression formation in Jining City, China. This paper investigates spatial groundwater overdraft severity by an index and Geographic Information System (GIS) method, and impact of artificial recharge on groundwater quality, by a 3-D groundwater flow finite difference numerical model code MODFLOW, and a solute transport model code MT3D. Hydrogeological and anthropogenic factors were evaluated. Groundwater concentration of chloride ions and total hardness (THD) as a result of artificial recharge were evaluated. The hydro-geochemical formation of the aquifer and recharge water quality greatly impact the groundwater quality. The recharge water must be within high groundwater quality standards.
Application of GIS-Based Spatially Distributed Hydrologic Model in Integrated Watershed Management:A Case Study of Nzoia Basin, Kenya
(Research Gate, 2010) Nyadawa, M. O.; Karanja, F.; Njoroge, T.; Otuoma, Sanya
The overall objective of this study was to study the impact of change of land use / land cover on catchment runoff response using FEWS-Flood Model as the rainfall-runoff conversion model in Nzoia basin, Kenya. Land use / land cover grid data were processed for the years 1986 and 2000 in IDRISI Kilimanjaro environment while both soil data and necessary meteorological data inputs were processed in necessary formats in ArcView. The study revealed that loss of forest cover between the year 1986 and 2000 equaled gain in acreage under cropland land/ woodland mosaic in the same period. Analysis of impact of change of land use/ land cover between 1986 and 2000 also revealed increased peaks in resulting hydrographs as a result of increased acreage under crops and reduced forest cover for same storm characteristics. This has given a rationale to recent increased flood disaster in the basin. Key Words: Nzoia, Integrated watershed management, USGS SFM, land use, land cover
'Kenya slum upgrading programme 'An anaysis of Kibera intergrated water, sanitation and waste management project
(University of Nairobi Research Archive, 2010) Walubwa, Jacqueline
Kenya has experienced rapid urbanization which has brought about many challenges, one of them being slum proliferation. This brings with it poor infrastructure delivery and a challenge in water and sanitation provision. Kenya, seeking to improve the lives of 5.3 million slum dwellers by 2020 (Kenya 2005) has set up a nationwide intervention in the slum areas. Kibera being one of the largest slum areas in Kenya was chosen as the pilot intervention site. This study was carried out in one of its villages- Soweto East- to determine the impact of the pilot intervention project (Kibera Integrated Water, Sanitation and Waste Management Project, K-WATSAN) being implemented by the Kenya Government and the UN HABITAT. Its main objective was to analyze the impact of the K-WATSAN intervention on the livelihoods of the residents. To achieve this objective the study utilized both secondary and primary sources of data and conducted a field study whereby questionnaires were administered in two villages- Lindi and Soweto East. The former acted as a control village as it had no intervention. Interview data was captured from selected respondents and was used to evaluate the livelihood, access to water and sanitation and community participation in the project. Content analysis and explotary data analysis were used to analyze the data using statistical tools of descriptive measures and methods of central tendencies; further statistical analysis on some selected variables was carried out to analyze the intervention's impact. The results indicated that K-WATSAN project has had a positive impact on the lives of the Soweto East residents in terms of; improved access to water and sanitation situation; improved accessibility and environmental conditions; improved sources of income and 'livelihoods security.The project has also achieved its aim of encouraging community participation in capacity building, empowerment and training of community members through the various trainings and Youth Empowerment Programme present in the settlement. The principles of inclusion, partnerships and sustainability have been reinforced through greater awareness, participation and partnerships in slum improvement. The study thus concluded that K-WATSAN project has had a positive impact in Soweto East and recommended embracing of community participation and proper governance mechanisms for any successful slum intervention on access to water and sanitation.
Relative abundance of mosquitoes and snails associated with water hyacinth and hippo grass in the Nyanza gulf of Lake Victoria
(Wiley, 2010-09-16) Ofulla, A.; Karanja, Diana; Omondi, Reuben; Okurut, T.; Matano, A.; Jembe, Tsuma; Abila, Richard; Boera, Priscilla; Gichuki, John
This study was conducted from September to December 2008 to investigate the relative abundance of malaria vectors and schistosomiasis host snails associated with aquatic weeds in Nyanza Gulf (Lake Victoria). Larval and adult’s stages of mosquitoes, lakeflies and snails were collected and identified with standard entomological and malacological techniques. The relative species composition and abundance of fish associated with macrophytes were also determined. Physico-chemical parameters were determined with standard analytical methods. Community-based surveys were also conducted, using standard questionnaires, focused group discussions and direct observations. The results of this study indicated that the abundance of malaria-causing mosquitoes was low, accounting for only 0.4% of the total number of mosquitoes and lake flies collected from the gulf. Lake flies (Chaoborus and Chironomus spp.) were the most abundant flying insects associated with aquatic macrophytes (84.2%), followed by Culicines Culex spp. (12.2%) and Aedes spp. mosquitoes (3.2%). Biomphalaria sudanica and Bulinus africanus, the two most common hosts for schistosomiasis in the gulf, were detected in both types of macrophytes, but were most significantly attached to water hyacinth (P < 0.0001) and hippo grass (P = 0.0003). There were significantly fewer snails attached to the hippo grass, compared with those unattached in the open water (P < 0.05, GENMOD). Different habitats exhibited low Secchi disc transparency values, but elevated total phosphorous (TP), total nitrogen (TN), chlorophyll-a concentrations, as well as algal cell counts. Furthermore, Oreochromis niloticus and Haplochromine fishes were more abundant in water hyacinth mats compared with hippo grass mats and open-water habitats. The low mosquito abundance indicated that the sampled habitats were unsuitable for mosquito breeding, likely attributable to water turbulence and/or predation by larvivorous fish. The strong association between B. sudanica and B. africanus and aquatic macrophytes, and the observation that local communities perform many lakeshore-related activities that bring them into contact with water, can potentially lead to a higher prevalence of schistosomiasis in the Nyanza Gulf region.
Physico-chemical charecteristics of Nyanza gulf in lake Victoria, Kenya.
(Semantic Scholar, 2011) Misiko, Florence Monicah; Radull, John; Gichuki, John; Andika, Darius O.
Kisumu Bay is greatly impacted by pollution from anthropogenic activities around Winam Gulf and from increased levels of industrial and municipal discharges from Kisumu town. This has resulted in significant changes in the trophic state and general ecology of the bay, impacting negatively on water quality, fisheries and livehoods. This study, therefore, aimed at determining the levels of physic-chemical parameters,nutrients and chlorophyll a in Kisumu Bay. Water quality measurements were conducted from April 2009-April 2010. Physico-chemical parameters (turbidity, temperature, conductivity, alkalinity, dissolved and suspended solids, and dissolved oxygen concentration) were measured using a sea bird, mult-parameter water quality probe, whereas nutrients (nitrates, nitrites and Phosphorous were analyzed by spectrophotometric techniques. There were significant spatial differences in the dissolved oxygen concentrations (p<0.0001) within the bay. These differences were especially pronounced at the Kisat, Maboko and Yatcht club stations which are associated with sewage discharge in Kisumu town. Similarly, significant differences (<0.05) associated with discharge from Kisumu town and seasonal nutrients runoffs from storm water were also observed in the spatial and temporal distribution of phosphorous ,ammonia, nitrates, nitrites and silicates within the gulf. Significantly, higher chlorophyll a concentrations were recorded during the dry season compared to the rainy season, probably as a result of high turbidity during the rainy season which reduces light penetration into the water. The study attributes this state of affairs to high nutrient loads from anthropogenic activities and industrial and municipal wastes and recommends stricter enforcement of the established policies on the quality of discharges from municipal and industrial establishments. There is also a need for environmental education and awareness creation targeting the lake communities to abate pollution in the lake.

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