Browsing by Author "Gichuki, John"
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Publication Importance of Indeginous Macrophytes in Control of Water Hyacinth in the Nyanza Gulf of Lake Victoria, Kenya.(Aquadocs, 2000) Omondi, Reuben; Gichuki, JohnObservation 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.Publication 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.Publication 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, JohnThis 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.Publication Water Hyacinth Eichhornia crassipes (Mart.) Solms-Laubach Dynamics and Succession in the Nyanza Gulf of Lake Victoria (East Africa): Implications for Water Quality and Biodiversity Conservation(The Scientific World Journal, 2012-04-19) Gichuki, John; Omondi, Reuben; Boera, Priscillar; Okorut, Tom; Matano, Ally Said; Jembe, Tsuma; Ofulla, AyubThis study, conducted in Nyanza Gulf of Lake Victoria, assessed ecological succession and dynamic status of water hyacinth. Results show that water hyacinth is the genesis of macrophyte succession. On establishment, water hyacinth mats are first invaded by native emergent macrophytes, Ipomoea aquatica Forsk., and Enydra fluctuans Lour., during early stages of succession. This is followed by hippo grass Vossia cuspidata (Roxb.) Griff. in mid- and late stages whose population peaks during climax stages of succession with concomitant decrease in water hyacinth biomass. Hippo grass depends on water hyacinth for buoyancy, anchorage, and nutrients. The study concludes that macrophyte succession alters aquatic biodiversity and that, since water hyacinth infestation and attendant succession are a symptom of broader watershed management and pollution problems, aquatic macrophyte control should include reduction of nutrient loads and implementing multifaceted approach that incorporates biological agents, mechanical/manual control with utilization of harvested weed for cottage industry by local communities.Publication Water hyacinth Eichhornia crassipes (Mart.) Solms-Laubach dynamics and succession in the Nyanza Gulf of Lake Victoria (east Africa): implications for water quality and biodiversity conservation(Hindawi Publishing Corporation, 2012) Gichuki, John; Omondi, Reuben; Boera, Priscillar; Okorut, Tom; Matano, Ally Said; Jembe, Tsuma; Ofulla, AyubThis study, conducted in Nyanza Gulf of Lake Victoria, assessed ecological succession and dynamic status of water hyacinth. Results show that water hyacinth is the genesis of macrophyte succession. On establishment, water hyacinth mats are first invaded by native emergent macrophytes, Ipomoea aquatica Forsk., and Enydra fluctuans Lour., during early stages of succession. This is followed by hippo grass Vossia cuspidata (Roxb.) Griff. in mid- and late stages whose population peaks during climax stages of succession with concomitant decrease in water hyacinth biomass. Hippo grass depends on water hyacinth for buoyancy, anchorage, and nutrients. The study concludes that macrophyte succession alters aquatic biodiversity and that, since water hyacinth infestation and attendant succession are a symptom of broader watershed management and pollution problems, aquatic macrophyte control should include reduction of nutrient loads and implementing multifaceted approach that incorporates biological agents, mechanical/manual control with utilization of harvested weed for cottage industry by local communities.Publication Water Hyacinth Eichhornia crassipes (Mart.) Solms-Laubach Dynamics and Succession in the Nyanza Gulf of Lake Victoria (East Africa): Implications for Water Quality and Biodiversity Conservation(Scientific World Journal, 2012-04-19) Gichuki, John; Omondi, Reuben; Boera, Priscillar; Okorut, Tom; Matano, Ally Said; Jembe, Tsuma; Ofulla, AyubThis study, conducted in Nyanza Gulf of Lake Victoria, assessed ecological succession and dynamic status of water hyacinth. Results show that water hyacinth is the genesis of macrophyte succession. On establishment, water hyacinth mats are first invaded by native emergent macrophytes, Ipomoea aquatica Forsk., and Enydra fluctuans Lour., during early stages of succession. This is followed by hippo grass Vossia cuspidata (Roxb.) Griff. in mid- and late stages whose population peaks during climax stages of succession with concomitant decrease in water hyacinth biomass. Hippo grass depends on water hyacinth for buoyancy, anchorage, and nutrients. The study concludes that macrophyte succession alters aquatic biodiversity and that, since water hyacinth infestation and attendant succession are a symptom of broader watershed management and pollution problems, aquatic macrophyte control should include reduction of nutrient loads and implementing multifaceted approach that incorporates biological agents, mechanical/manual control with utilization of harvested weed for cottage industry by local communities.