Browsing by Author "Ojwang, William"

Now showing 1 - 5 of 5
  • Publication
    Publication
    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.
  • Publication
    Publication
    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 Journal, 2013-12-30) 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
  • Publication
    Publication
    Composition, Abundance and Feeding Guilds of Macroinvertebrates in Lake Kenyatta, Kenya
    (International Journal of Environmental Monitoring and Analysis, 2014-09-30) Orwa, Patrick Oduor; Omondi, Reuben; Okuku, Eric; Ojwang, William; Njuguna, Stephen Mwangi
    In an attempt to describe the benthic macroinvertebrate assemblage of Lake Kenyatta and recommend possible interventions for sustainable management, sampling was done at different stations using an Eckman grab and a scoop net. At each station, six samples were taken (three grabs and three scoops). The samples were washed using a 300µm sieve, sorted live and identified to genus level and where possible to species level using appropriate keys. The specimens were further categorized into functional feeding guilds. The data were then analysed for diversity, evenness, abundance and dominance. Forty two species in 25 families and 13 orders were recorded. The organisms were further grouped into 4 functional feeding groups. The order Pulmonata dominated the macroinvertebrates sampled with 34.3% relative abundance while the lowest were Rhynchobdellida and Lepidoptera with 0.3% each. The high abundance of mollusks in the lake is probably an indication of absence of a predator. It is thus recommended that a fish species be introduced to convert these mollusks into fish biomass. This will enhance the economic gains and reduce the risk of bilhazia infestation since the host snail exists within the lake.
  • Publication
    Publication
    Intriguing case of ecosystem dynamics in the Lake Victoria: Water Hyacinth (Eichhornia crassipes) and Escherichia coli
    (International Journal of Fisheries and Aquatic Studies, 2015-03-15) Mutie, Alice; Ojwang, William; Werimo, Kenneth; Omondi, Reuben; Ouko, John
    Water hyacinth (Eichhornia crassipes) is a noxious weed with immense impact on the health and the livelihoods of communities’ in the tropical sub-Saharan African countries. This study was aimed at assessing the effects of water hyacinth on Escherichia coli levels in Kenyan Lake Victoria. Sampling was done in waters infested by water hyacinth (roots and mats) and in open water areas (devoid of the weed). Membrane filtration method was used to enumerate Escherichia coli at 44.5 ºC for 18-24 h. Results showed that E. coli levels were higher in water hyacinth infested areas compared to areas in the open waters and those under water hyacinth mats. The levels of E. coli in the open water areas ranged from undetectable levels to 1140 cfu/100 ml. Whereas, levels of E. coli from areas under water hyacinth mats ranged from 10 cfu/100 ml to 1549 cfu/100 ml while E. coli levels from waters from water hyacinth roots ranged from undetectable levels to 6387 cfu/100 ml. Therefore, general marked differences in levels of E.coli in hyacinth thriving areas with regard to free areas indicate potential ability of the plant to harbor microbiological contaminants and if its spread is left unchecked, incidences of water borne related diseases like the cholera may increase incredibly among the riparian communities with consequent loss of many lives. It is therefore imperative that a plan of action is put in place to control the spread of water hyacinth in Lake Victoria.
  • Publication
    Publication
    Lakes Baringo and Naivasha: Endorheic Freshwater Lakes of the Rift Valley (Kenya)
    (Springer, Dordrecht, 2018-05-16) Omondi, Reuben; Ojwang, William; Olilo, Casianes; Mugo, James; Agembe, Simon; Ojuok, Jacob E.
    Lakes Baringo and Naivasha are among the Great Rift Valley lakes that were formed about 25 million years ago by violent separation of two of the earth’s continental plates floating on the molten magma of its core. Lake Baringo is a freshwater lake in the eastern arm of Kenya’s Great Rift Valley, with surface and catchment areas of approximately 130 and 6,820 km2, respectively, and a mean depth of 5.9 m. The lake is shallow and is virtually a wetland in its entirety, with submerged Ceratophyllum demersum occurring in the deepest portions of the lake. However, larger marshes are found at the river mouths to the south and east. Lake Naivasha has a surface area of approximately 119,130 km2, a catchment area of 3,200 km2, and a mean depth of 4.1 m. Lake Naivasha’s water level has experienced great fluctuations sometimes as much as 7 m over many years attributed to large-scale climatic influence, also causing changes in water geochemistry. The main lake has a fringing vegetation of Cyperus papyrus and other macrophytes and the lake body supports a diverse macrophyte community. In addition to the lakes’ high biodiversity, they provide water to the local communities for domestic, irrigation, and industrial purposes. Fish in these lakes contribute to the diet of the local communities and are a source of income. Due to their unique scenery and biodiversity, the lakes are destinations for both local and international tourists. Lakes Baringo and Naivasha are faced with numerous threats and challenges including an increasing human population, deforestation and erosion, pollution, impacts associated with tourism, human–wildlife conflict, impact of invasive species, and climate change. Investments around these lakes need to be balanced against the threats to biodiversity and the human population.