Implications of the ever-increasing population of water hyacinth on the fishing industry

Introduction

Fresh water bodies constitute a vital component of a wide variety of living environments as integral water resource base in many human societies in the world. They have been regarded as key strategic resources essential for sustaining human livelihood, promoting economic development and maintaining the environment (Uganda National Water Development Report (UNWDR), 2005). Utilization of freshwater resources include use as source of drinking water, fishing activities, sites for domestic and industrial effluents discharge, recreation and transportation activities.

Water hyacinth, a floating vascular plant, is known to cause major ecological and socio-economic changes (Center, 1994). Originally from South America, water hyacinth is one of the world’s most prevalent invasive aquatic plants. It has become naturalized in many warm areas of the world. Water hyacinth has invaded freshwater systems in over 50 countries on five continents; it is especially pervasive throughout Southeast Asia, the southeastern United States, central and western Africa, and Central America (Bartodziej & Weymouth, 1995; Brendonck et al., 2003; Lu et al., 2007; Martinez Jimenez and Gomez Balandra, 2007).

The first reference to water hyacinth in the United States was at the beginning of the 20th century on the occasion of the Louisiana Purchase (Sculthorpe 1967). The spread continued to Florida where there are many references to control the spread and infestations that occurred (Schardt 1984). It was also introduced into North and South Carolina. In the countries of South America, there are reports of its presence in 1902 in Brazil, 1942 in Argentina, 1959 in Paraguay, Uruguay, Bolivia, Ecuador, and Colombia, 1976 in Venezuela, and 1979 in Chile. In Central America, it is cited in Mexico, Nicaragua, Costa Rica, and El Salvador in 1965, Panama in 1966, and Puerto Rico and the Dominican Republic from 1971. Water hyacinth grows rapidly (Penfound and Earle, 1948) forming expansive colonies of tall, interwoven floating plants. It blankets large waterbodies, creating impenetrable barriers and obstructing navigation (Gowanloch and Bajkov,1948; Zeiger, 1962). It has been reported that floating mats block drainage, causing flooding or preventing subsidence of floodwaters. Large rafts accumulate where water channels narrow, sometimes causing bridges to collapse. Water hyacinth hinders irrigation by impeding water flow, by clogging irrigation pumps, and by interfering with weirs (Penfound and Earle, 1948).

In Europe, the water hyacinth was possibly introduced as an ornamental plant in the first third of the 20th century in Portugal, because the first reference to its presence there dates from 1939. Since then, it has spread over the central-west of the country through irrigation canals and currently exists in the middle and lower Sado and Tagus Basins (Guerreiro 1976; Figueiredo et al. 1984; Amaral and Rocha 1994). Hyacinth infestations block access to recreational areas and decrease waterfront property values, oftentimes harming the economies of communities that depend upon fishing and water sports for revenue. Shifting water hyacinth mats sometimes prevent boats from reaching shore, trapping the occupants and exposing them to environmental hazards (Harley, 1990). Water hyacinth infestations intensify mosquito problems by hindering insecticide application, interfering with predators, increasing habitat for species that attach to plants, and impeding runoff and water circulation (Seabrook, 1962).

In Africa, the water hyacinth was first reported in Egypt between 1879. It is considered one of the most notorious weed species in tropical West Africa (Food and Agriculture Organization (FAO), 2000). Water hyacinth infestation of freshwater ecosystems has been recently reported by several workers (Luken and Thieret, 1997; Bolorunduro, 2000; Osumo, 2001; Masami et al., 2008); and its major effect appears to be disruption of normal ecological functioning of aquatic ecosystems where it is found thriving. Beneficial effects of the water hyacinth have also been reported as an aid in water purification through conversion of toxic ammonia to usable nitrates as well as capacity to absorb heavy metals and organic compounds from water body (Simeon et al., 1987; Cowx and Welcomme, 1998; Ingole and Bhole, 2002). The influence of aquatic macrophytes on the limnological properties of water bodies has been recognized (Petre, 2000; Lee and McNaughton, 2004). They may, therefore, be regarded as efficient indicators of water quality. The weed was first reported in the Ugandan portion of Lake Victoria in 1990 (Thompson, 1991). It is believed that it entered the lake in 1989 via the Kagera River, which has its mouth in the Ugandan portion of the lake (Muli 1996). Estimates made in April 1999 and in August 1999 indicated that the input of water hyacinth into Lake Victoria through the River Kagera was 3.5 ha per week (Mailu, 2001).

According to Mailu, the water hyacinth infestations in the portion of Lake Victoria in Tanzania in 1999 were located in Mara Bay, Bauman Gulf, Speke Gulf, Mwanza Gulf, Emin Pasha Gulf and Rubafu Bay. Currently, water hyacinth occurs also in the Kagera, Sigi and Pangani rivers, as well as in streams and water ponds around Dar-es-Salaam and close to Lake Victoria. The total cover estimate of water hyacinth in the Tanzanian waters of Lake Victoria was 2000 ha (Mailu, 2001).

Water hyacinth was first sited in the Kenyan side of the lake in 1992 (Republic of Uganda, 2005). Water hyacinth occurred in form of stationary mats in sheltered bays and along much of the lakeshore, in addition to the mobile mats that were propelled around the lake by winds, waves and water currents (Balirwa, Wanda, and Muyodi, 2009). Despite water hyacinth’s invasive nature and dominance in Lake Victoria in the 1990s, water hyacinth largely disappeared from Lake Victoria by the end of 1999. For instance, no water hyacinth was found on the Gulf from April 2002 until October 2004, only appearing again at the next measurement date of December 2005 (Gichuki et al, 2011).

At the Winam Gulf in Lake Victoria the water hyacinth is mainly found in inshore and shallow areas to which it is swept by currents and sometimes in patchy offshore areas. It spreads fast in shallow (< 6m) bays and inlets with mud bed surfaces. Lake Victoria’s tropical location, shallow depth and nutrient enrichment provide favorable conditions for its proliferation. The ‘mats’ of aquatic plants reduce dissolved oxygen by restricting the exchange of oxygen across the air/water interface. They also affect wind-driven water movement and impede mixing of oxygen-rich surface water (Smith-Rogers, 1999). The oxygen can be reduced to such low levels that it leads to massive fish kills due to oxygen depletion in the water column, this result in loss of aquatic biodiversity (Muli, 1996). The plant can also block waterways, such as fish landing beaches and piers and prevent boats from docking thus hindering transportation by the fishermen.

The spread of invasive alien species is neither easy to manage nor easy to reverse, threatening not only biodiversity but also economic development and human wellbeing (UNEP, 2012). Native to the Amazon Basin in South America water hyacinth has emerged as a major weed in more than 50 countries in the tropical and subtropical regions of the world with profuse and permanent impacts (Patel 2012, Téllez et al, 2008, Shanab et al, 2010, Villamagna and Murphy 2010). Worryingly, climate change may allow the spread of water hyacinth to higher latitudes (Patel, 2012). Intensified monitoring, mitigation and management measures are needed to keep water hyacinth at unproblematic levels

It is widely reported that water hyacinth is indigenous to Brazil having first been described from wild plants collected from Francisco River in 1824. In Africa it was first reported in Egypt between 1879 and 1893. By the early 1990s it had spread to virtually every country in the continent (Makhanu, 1997).

It was first reported in the Ugandan portion of Lake Victoria in 1990 (Thompson, 1991). It is believed that it entered the lake in 1989 via the Kagera River, which has its mouth in the Ugandan portion of the lake (Muli, 1996). It is not exactly known when it entered Winam Gulf.

Water hyacinth (Eichhornia crassipes) is a freshwater weed species. It is a free floating plant and draws all its nutrients directly from water. Currents and wind help in its distribution and dispersal. It comprises 95% water and 5% per cent dry matter of which 50% is silica, 30% potassium, 15% nitrogen and 5% protein (Makhanu, 1997). It has been known to thrive well in nutrient-enriched fresh waters in tropical climatic zones. For this purpose it has been used in wastewater treatment facilities. The weed is mainly found in inshore and shallow areas to which it is swept by currents and sometimes in patchy offshore areas. It spreads fast in shallow (< 6m) bays and inlets with mud bed surfaces. Lake Victoria’s tropical location, shallow depth and nutrient enrichment provide favourable conditions for its proliferation (Mitchell, 1976).

Related Topic  Ecological and health implications of open pit artisanal gold mining

Water hyacinth has limited beneficial uses. It cannot be used as a livestock feed because it contains too much silica, calcium oxalate, potassium and too little protein. It cannot be directly used as a fertilizer because its C:N ratio is too high necessitating addition of N-fertilizer (Makhanu, 1997).

Its economic significance stems from its potential to produce negative consequences for the habitat quality of water bodies. The ‘mats’ of aquatic plants reduce dissolved oxygen by restricting the exchange of oxygen across the air/water interface. They also affect wind-driven water movement and impede mixing of oxygen-rich surface water (Smith-Rogers, 1999). It also generates large amounts of organic matter. As the organic matter decomposes, biological oxygen demand increases and water quality deteriorates. The oxygen can be reduced to such low levels that it leads to massive fish kills due to oxygen depletion in the water column (Ochumba and Kibaara, 1989). This results in loss of aquatic biodiversity (Muli, 1996).

In shallow lakes and where plant production is great, complete deoxygenation of the sediments and deeper water can occur. Such conditions are not compatible for the survival of fishes and invertebrates. Moreover, under anoxic conditions, ammonia, iron, manganese and hydrogen sulphide concentrations can rise to levels deleterious to biota. In addition, phosphate and ammonium are released into the water from anoxic sediments, further enriching the ecosystem (International Development Research Centre, 2000).

The plant can also block waterways, such as Kisumu harbor and fish landing beaches and piers and prevent boats from docking. The plant can clog irrigation canals and electricity generating turbines and its presence can be a general risk to public health.

Water hyacinth and the fishing industry

The fisheries sub-sector plays an important role in Kenyan economy. The sector provides employment to over 500,000 Kenyans engaged in fish production and fish related enterprises. The fisheries sub-sector is however unable to realize its full potential due to among other factors over-reliance to capture fisheries and environmental degradation (Wafula et al, 2005).

Water hyacinth affects access to fishing grounds and fish catch-ability (Kateregga & Sterner, 2009). Reports from around the world indicate some villages where people have died from heavy water hyacinth infestations; notably through starvation because they could not reach food sources and protein deficiency resulting from unavailability of fish (Navarro & Phiri, 2000). Water hyacinth causes severe problems to fishermen in the riparian communities. When weed infestation is present, access to fishing sites become difficult for riparian communities which rely solely on fishing as their main economic activity (Munjigni, 2001). This leads to increase in their expenditure on fuel for engine boats and further increase in the cost of the meager quantities of fish they catch, for the society as a whole. There is often loss of fishing gears when nets or lines become tangled in the root systems of the weed. All these lead to reduction in fish catch and subsequent loss of livelihood. Center et al. (2002) reported that water hyacinth invasions reduce available light for submerged plants hence depleting oxygen, alters the composition of invertebrate communities, impacts fisheries, displaces native plants and wildlife, and increases sediment loading.

Information from the Fisheries Department, Kenya according to Mailu (2001) indicated that there was a 28% increase in total annual fish catches between 1986–1991 and 1991–1997, from 133,097 tonnes to 169,890 tonnes. There was an increase in all species of fish caught except Oreochromis, Clarias and Mormyrus, which showed declines of 14, 37 and 59%, respectively, over the same period. These declines may have been associated with the inability of fishermen to access the fishing grounds for those species because of water hyacinth infestation. Generally therefore, as a result of water hyacinth infestation, accessibility to land and water has been hindered, resulting in reduced fish catches, especially of tilapia and mudfish which are found mainly along the shores. Fisherfolk, however, reported increased fish catches from suitable breeding grounds provided by water hyacinth e.g. tilapia, synodontis, protopterus and labeo. A reduced fish catch would have an adverse effect on the quality of life of the communities around the lake and consequently affect sustainable development in the region.

Water hyacinth can greatly affect a fishery if it induces changes in fish community composition, or if catch-ability of harvested species is changed. Diversity in fish stocks is often affected with some benefiting and others suffering from the proliferation of water hyacinth (Calvert, 2002). In Lake Victoria, fish catch rates decreased because water hyacinth mats blocked access to fishing grounds, delayed access to markets, and increased fishing costs (effort and materials) (Kateregga & Sterner, 2009). Mats also blocked breeding, nursery, and feeding grounds for economically important species, such as tilapia and Nile perch in Lake Victoria (Twongo & Howard, 1998). It is interesting to note that decreased catch-ability of certain overfished species can lead to increased fishery stocks (Kateregga & Sterner, 2009) that in the long-run could benefit a fishery and human society.

The water hyacinth is an important fish feed. The Chinese grass carp is a fast growing fish which eats aquatic plants. It grows at a tremendous rate and reaches sizes of up to 32 kg (National Academy of Science (NAS), 1979). It can eat both submerged and floating plants. The fish can be used for weed control and will eat up to 18 – 40% of its own body weight in a single day (Gopal, 1987). Also, dehydrated water hyacinth has been added to the diet of channel catfish fingerlings to increase their growth, hence used indirectly to feed fish (Gopal, 1987). According to Gopal, 1987 decay of water hyacinth after chemical control also releases nutrients which promote the growth of phytoplankton with subsequent increases in fish yield.

Fishing production

The infestation of water bodies by water hyacinth resulted in a reduction in levels of fish production and species composition of the catch. The fish caught is of poor quality and the cost of operation and maintenance has increased resulting to lower incomes to the fishermen and escalating prices to consumers. Large mats of the weed also sweep away the entangle fleets of nets and poses as a major obstruction to fisheries operation (KARI/LVEMP, 2004) The vegetation may be good for the ecosystem as fish can reproduce and grow to full size before they are harvested. The weed and its impacts affect 44,000 fishermen and their families, who depend on the lake directly. The vegetation covers hinders of the lake and has raised concerns. Experts say haplochromis, locally known as “fulu” was a staple food and an indicator of bio-diversity in the lake four decades ago. The species was believed to be extinct after the colonial government introduced Nile perch, which fed on them, in 1960s.Nile perch has since been over fished (Nkuba, 1998). The five-centimeter bony fish is a delicacy for its nutritional Value. Known as ‘furu’ in Uganda and Tanzania it comprised more than 70% of fish in the Lake (The Standard Newspaper, 2008).

In Kenya, Information from the fisheries department indicated that there was an increase of the total annual fish catches from 133,097 tons in 1986-1990 to 169,890 tons in (1991-1997). There was an increase in fish caught in all aspects expect oveochrimics, larus and marymyrus hich indicated that at 14%, 37% and 59% decline over the same period. It should be noted that whilst hyacinth plants provide food for fish in some measures the deoxygenated problem associated with the excessive growth causes more serious interference with fisheries (KARI/LVEMP, 1999)

Related Topic  Street Hawking and its Impacts on Urban Space

Impacts of water hyacinth

a.) Destruction of biodiversity

Today, biological alien invasions are a major driver of biodiversity loss worldwide, (Pyšek and Richardson 2010, Vila et al. 2011). Water hyacinth is challenging the ecological stability of freshwater water bodies (Khanna et al, 2011, Gichuki et al, 2012), out-competing all other species growing in the vicinity, posing a threat to aquatic biodiversity (Patel, 2012). Besides suppressing the growth of native plants and negatively affecting microbes, water hyacinth prevents the growth and abundance of phytoplankton under large mats, ultimately affecting fisheries (Gichuki et al, 2012, Villamagna and Murphy, 2010).

b.) Oxygen depletion and reduced water quality

Large water hyacinth mats prevent the transfer of oxygen from the air to the water surface, or decrease oxygen production by other plants and algae (Villamagna and Murphy, 2010). When the plant dies and sinks to the bottom the decomposing biomass depletes oxygen content in the water body (EEA, 2012). Dissolved oxygen levels can reach dangerously low concentrations for fish that are sensitive to such changes. Furthermore, low dissolved oxygen conditions catalyze the release of phosphorus from the sediment which in turn accelerates eutrophication and can lead to a subsequent increase in water hyacinth or algal blooms (Bicudo et al, 2007). Death and decay of water hyacinth vegetation in large masses deteriorates water quality and the quantity of potable water, and increases treatment costs for drinking water (Patel 2012, Mironga et al, 2011, Ndimele et al, 2011).

c.) Breeding ground for pests and vectors

Floating mats of water hyacinth support organisms that are detrimental to human health. The ability of its mass of fibrous, free-floating roots and semi-submerged leaves and stems to decrease water currents increases breeding habitat for the malaria causing anopheles mosquito as evidenced in Lake Victoria (Minakawa et al. 2008). Mansonioides mosquitoes, the vectors of human lymphatic filariasis causing nematode Brugia, breed on this weed (Chandra et al. 2006, Varshney et al, 2008). Snails serving as vector for the parasite of Schistosomiasis (Bilharzia) reside in the tangled weed mat (Borokini and Babalola, 2012). Water hyacinth has also been implicated in harboring the causative agent for cholera. For example, from 1994 to 2008, Nyanza Province in Kenya, which borders Lake Victoria accounted for a larger proportion of cholera cases than expected given its population size (38.7% of cholera cases versus 15.3% of national population). Yearly water hyacinth coverage on the Kenyan section of the lake was positively associated with the number of cholera cases reported in the Province (Feikin et al, 2010). At the local level increased incidences of crocodile attacks have been attributed to the heavy infestation of the weed which provides cover to the reptiles and poisonous snakes (Patel 2012, Ndimele et al, 2011).

d.) Blockage of waterways hampering agriculture, fisheries, recreation and hydropower

Water hyacinth often clogs waterways due to its rapid reproduction and propagation rate. The dense mats disrupt socioeconomic and subsistence activities (ship and boat navigation, restricted access to water for recreation, fisheries, and tourism) if waterways are blocked or water pipes clogged (Ndimele et al, 2011, Patel 2012). The floating mats may limit access to breeding, nursery and feeding grounds for some economically important fish species (Villamagna and Murphy, 2010). In Lake Victoria, fish catch rates on the Kenyan section decreased by 45% because water hyacinth mats blocked access to fishing grounds, delayed access to markets and increased costs (effort and materials) of fishing (Kateregga and Sterner, 2009).

Socio-economic impacts of water hyacinth

Water hyacinth infestation as from 1992, when it was first seen in Lake Victoria, the Winam Gulf, it has caused a lot of impacts to the community livelihoods. The weed’s infestation has several effects which is associated with which has reduced the fishermen’s performance towards fishing production; these are things like diseases, reduced water quality, loss of recreation areas, reduction in transportation among other effects. Since the community depends on Lake Victoria for their sources of income.

Most water bodies are a source food, energy, drinking, Irrigation, transportation and repositories for human agriculture and industrial wastes. Most of these water bodies are infested with water hyacinth which is considered the most noxious of all aquatic weeds and ranked as 8th among the word’s weed (Varnshney, 1976).

Theoretical framework

The study was based on the Opportunity-Based Entrepreneurship theory by (Drucker, 1985). The theory asserts that entrepreneurs do not cause change but exploit the opportunities that change creates (change in technology, consumer preferences etc.) (Drucker, 1985). The entrepreneur always searches for change, responds to it, and exploits it as an opportunity. What is apparent in Drucker’s opportunity construct is that entrepreneurs have an eye more for possibilities created by change than the problems.

Stevenson (1990) extends Drucker’s opportunity-based construct to include resourcefulness. He concludes that the hub of entrepreneurial management is the pursuit of opportunity without regard to resources currently controlled. Entrepreneurs identify business opportunities to create and deliver value for stakeholders in prospective ventures. While elements of opportunities may be recognized, opportunities are made, not found. Careful investigation of and sensitivity to market needs and as well as an ability to spot suboptimal deployment of resources may help an entrepreneur begin to develop an opportunity (which may or may not result in the formation of a business). But opportunity development also involves entrepreneurs’ creative work. Therefore, ‘‘opportunity development’’ rather than ‘‘opportunity recognition,’’ was the focus of this study. In this study, the residents around the Winam Gulf, in spite of the problems created by the presence of the water hyacinth on the surface of Lake Victoria, some take advantage of the entrepreneurial opportunities created by its infestation while others premise their entrepreneurial activities on the absence of the water hyacinth.

Conceptual framework

The conceptual framework in the figure shows the relationship between the independent variable (water hyacinth) and the dependent variables (economic activities). It was conceptualized that when water hyacinth covers the water surface, extraction of water from the lake is hampered leading to harvesting of lower volumes of water than the operational capacity of the water treatment plant. The hyacinth also affects the chemical composition of the water. The low water volumes reduce the water business activities that affecting the livelihoods of the people who depend on the business for their livelihoods.

With regard to the fishing industry, it was conceptualized that the coverage of the water by the water hyacinth impedes fishing thus reducing the number of fish caught. The water hyacinth entangles the fishing equipment, making fishing difficult. However, on a positive front, the water hyacinth may be eaten by the fish as feed and therefore increase the fish population.

When the hyacinth is harvested, it may be used as raw material in the weaving industry for making some forms of furniture, baskets, ropes and other craft that are sold to earn income. Some of the items made from the hyacinth may attract tourists thus promoting tourist activities. On the other hand, the water hyacinth may block the water ways thus affecting navigation of boats, which greatly affects tourism and other recreational activities.

The interaction between the water hyacinth and the economic activities may be moderated by seasonal movements of the water hyacinth which either opens up the water or covers the water surface thus impeding any activities on the surface. The level of infestation of the hyacinth also determines the level of exposure of the water surface to allow for both biological activities and other human activities in the water. When the water hyacinth is harvested as raw material for various basketry and craft products, water surface is opened up to allow for the mentioned processes to take place. On the other hand, the toxicity of the water may influence all the biological processes, production and use of the water.

Conclusion

Aquatic weeds including water hyacinth have always existed but in recent decade their effects/impacts have been magnified by man’s more intensives use of natural water bodies by modifying them into canal and dams; polluting the water bodies with farm inputs and urban waste waters, introducing aggressive plant species into new location among other means. Eradication of the weed (water hyacinth) has proved almost impossible making even control difficult.

Related Topic  The pains and gains associated with restoring the Mau Narok Forest, Kenya

As the serious negative implication of the presence of water hyacinth become more widely recognized, the locals and institutions concerned should focus their attention more on the positive effects of the weed; water hyacinth for instance, has the ability to remove toxic heavy metals (copper, lead cadmium, chromium and manganese) from aqueous system during production of large amount of plant biomass.

It is argued that the utilization of the weed may be the best way to control it as it helps to minimize the economic input, it is environmentally sound and at the same time it provides some of the much needed resources.

Turning this weed to productive use would look or seem desirable but only limited research has so far been carried out and it’s long term consequences (i.e. 50-100 years to come) are unknown.

There may be some beneficial effects of water hyacinth through provision of suitable breeding ground for fish and use of this weed for making handicrafts, furniture, papers, or used as fertilizers and as mulch, but with heavy infestation these benefits are surpassed by the negative effects. For this reason, the following recommendations may help to accentuate the control measures in place.

Recommendations

Community sensitization and participation programmes should be initiated and strengthened. The study reveals that most local residents do not know or appreciate the role of the government and thus the lack the urge to participate in it anyway:

  • The major and the main recommendation is to provide disposal sites along the shores of lake Victoria; community will be paid according to dry water hyacinth they will collect and bring for weighing.
  • The government should come up with efficient and effective policies and legislations to control fishing so as to avoid over fishing.
  • There is need for constant monitoring of water hyacinth to aid in its control
  • The fact that most of the effluent to the lake takes place in the gulf (231 m3s-1) and the only outlet being in the extreme opposite of the gulf, this would create a pressure along the channel through which the outflow occurs and there should be a near permanent flow from the gulf to the main lake. Determination of water budgets into and out of the gulf should be incorporated into some future study. This could help generate information on the occasional flooding in the Gulf

 

Recommendations to the communities

The locals should actively and genuinely participate in efforts to control the spread of weed, for instance through:

  • Avoid transportation of the weed from one point to another.
  • Engage in other income earning activities other than fishing which is greatly hampered by water hyacinth.

Bibliography

Bicudo, D., Fonseca, B., Bini, L., Crossetti, L., Bicudo, C. and Araujo-Jesus, T., 2007. Undesirable side-effects of water hyacinth control in a shallow tropical reservoir. Freshwater Biology, 52, 1120–1133.

Borokoni, T. and Babalola, F., 2012. Management of invasive plant species in Nigeria through economic exploitation: lessons from other countries. Management of Biological Invasions 3 (1): 45–55 doi: http://dx.doi.org/10.3391/mbi.2012.3.1.05.

Calvert, P. (2002). Water Hyacinth: Control and possible uses. Practical Action, The Schumacher Centre for Technology and Development, Bourton on Dunsmore, Rugby,Warwickshire, UK

Chandra, G., Ghosh, A., Biswas, D. and Chatterjee, S., 2006. Host plant preference of Mansonia mosquitoes. J Aquatic Plant Manage 44:142–144.

EEA, 2012. The impacts of invasive alien species in Europe. EEA Technical report No 16/2012. Luxembourg: Publications Office of the European Union, 2012. http://www.eea.europa.eu/publications/impacts-of-invasive-alien-species (accessed 12 March 2013).

Feikin, D., Tabu, C. and Gichuki, J., 2010. Does water hyacinth on East African lakes promote cholera outbreaks? American Journal of Tropical Medicine and Hygiene 83: 370–373. doi:10.4269/ajtmh.2010.09-0645.

Gichuki, J., Omondi, R., Boera, P., Tom Okorut, T., SaidMatano, A., Jembe, T. and Ofulla, A., 2012. Water Hyacinth Eichhornia crassipes (Mart.) Solms-Laubach Dynamics and Succession in the Nyanza Gulf of Lake Victoria (East Africa): Implications forWater Quality and Biodiversity Conservation. The Scientific World Journal Volume 2012, Article ID 106429, 10 pages doi:10.1100/2012/106429.

Gopal, B. (1987). Water Hyacinth. Elsevier Science Publishers, Amsterdam, The Netherlands.

Gowanloch, J. N. (1944). The economic status of the water hyacinth in Louisiana. Louisiana Conservationist 2: 3-8.

Guerreiro, A.R. (1976) O Jacinto aquatico (Eichhornia crassipes (Mart) Solms) em Portugal. Paper presented at II Simposio Nacional de Herbologia, Oeiras (Portugal), 6-7 Dec 1976 Jianqing D, Ren.

Kateregga, E. and Sterner, T., 2009. Lake Victoria fish stocks and the effects of water hyacinth. The Journal of Environment & Development, 18, 62–78.

Khanna, S., Santos, M., Ustin, S., Haverkamp, P., 2011. An integrated approach to a biophysiologically based classification of floating aquatic macrophytes. Int. J. Remote Sens 32:067–1094.

Mailu, A.M. (2001). Preliminary assessment of the Social, Economic and Environmental Impacts of water hyacinth in the Lake Victoria basin and the status of control. In: Biological and Integrated control of water hyacinth, Erchhorniacrassipes. Julien, M.H., M. P. Hill, T. D. Centre and D. Jianqung (Eds)., ACIAR proceedings 102, 130–139. Retrieved from http://ageconsearch.umn.edu/bitstream/135372/2/PR102.pdf.

Makhanu K.S. 1997. Impact of Water hyacinth in Lake Victoria. In: Water and Sanitation for all: Partnerships and Innovations. 23rd Water Engineering and Development Centre Conference Durban, South Africa.

Minakawa, N., Sonye, G., Dida, G., Futami, K. and Kaneko, S., 2008. Recent reduction in the water level of Lake Victoria has created more habitats for Anopheles funestus. Malaria J 7:119.

Mironga, J., Mathooko, J. and Onywere, S., 2011. The Effect of Water Hyacinth (Eichhornia Crassipes) Infestation on Phytoplankton Productivity in Lake Naivasha and the Status of Control. Journal of Environmental Science and Engineering 5(10) 1252-1261.

Mitchell D.S. 1976. ‘The growth and management of Eichhornia crassipes and salvinia spp. in their native and alien situations’. In Varshney C.K and Rzoska J. eds. Aquatic weeds in South East Asia. The Hague: Junk

Mujingni, C., (2012). Quantification of the impacts of Water Hyacinth on riparian communities in Cameroon and assessment of an appropriate method of control: The case of the River Wouri Basin: The Case of the Wouri River Basin. Msc disseratation. World Maritime University, Malmö, Sweden.

Muli R.J. 1996. Environmental problems in Lake Victoria (East Africa): What the international Community can do. Lakes and Reservoirs: Research and Management. 2:47-53. Nairobi. Kenya.

National Academy of Sciences, NAS (1976). Making Aquatic Weeds Useful: Some Perspectives for Developing Countries. National Academy Press, Washington DC.,pp: 175.

Ndimele, P. and Jimoh, A., 2011. Water Hyacinth (Eichhornia crassipes [Mart.] Solms.) in Phytoremediation of heavy Metal Polluted Water of Ologe lagoon, Lagos, Nigeria. Research journal of Environmental Sciences, 5(5), 424-433. DOI: 10.3923/rjes.2011.424.433.

Ochumba P.B.O and D.I. Kibaara 1989. Observation on blue-green algae blooms in the open waters of Lake Victoria, Kenya. African Journal of Ecology. 27: 23-34.

Patel, S. , 2012. Threats, management and envisaged utilizations of aquatic weed Eichhornia crassipes: an overview. Rev Environ Sci Biotechnol (2012) 11:249–259. DOI 10.1007/s11157-012-9289-4.

Penfound, W. T. and T. T. Earle. (1948). The biology of the water hyacinth. Ecological Monographs 18: 447- 472.

Pyšek, P., and Richardson, D., 2010. Invasive species, environmental change and management, and health. Annual Review of Environment and Resources 35: 25–55. doi: 10.1146/annurevenviron- 033009-095548.

Sculthorpe, C. D. (1967) The Biology of Aquatic Vascular Plants. Edward Arnold, London. Seabrook, E. L. (1962). The correlation of mosquito breeding to hyacinth plants. Hyacinth Control Journal 1: 18-19.

Smith-Rogers, S. 1999. Effect of aquatic weeds on water quality. [12 March 2000] http://www.hydrolab.com/htmla2.htm

Thompson K. 1991. The ecology of water hyacinth and its distribution in Uganda. In K. Thompson ed. Water hyacinth in Uganda: Ecology, Distribution, Problems and Strategies for Control. Proceedings of a National Workshop, 22 –23 October 1991, Kampala, Uganda. UN/FAO.

Villamagna, A. and Murphy, B., 2010. Ecological and socio-economic impacts of invasive water hyacinth (Eichhornia crassipes): a review. Freshwater Biology (2010) 55, 282–298 doi:10.1111/j.1365-2427.2009.02294.x.

Wafula, M. Mbith,i M. and Mwangi, J. (2005) the Kenya fisheries sub sector: Nature of legislation practices, administrative weakness, threats and the way forward, African Centre for economic Growth, Westlands, Nairobi Kenya.

Leave a Comment Here