WATER HYACINTH CONTROL AND POSSIBLE USES

1 WATER HYACINTHCONTROL AND POSSIBLE USESI ntroductionWater HYACINTH (Eichhornia Crassipes) WATER HYACINTH is an aquatic plant which can live and reproduce floating freely on the surface offresh waters or can be anchored in mud. Plant size ranges from a few inches to a metre inheight. Its rate of proliferation under certain circumstances is extremely rapid and it canspread to cause infestations over large areas of WATER causing a variety of problems. It growsin mats up to 2 metres thick which can reduce light and oxygen, change WATER chemistry,affect flora and fauna and cause significant increase in WATER loss due to evapotranspiration. Italso causes practical problems for marine transportation, fishing and at intakes for hydro powerand irrigation schemes. It is now considered a serious threat to plant originated in the Amazon Basin and was introduced into many parts of the world asan ornamental garden pond plant due to its beauty.

2 It has proliferated in many areas and cannow be found on all continents apart from Europe. It is particularly suited to tropical and sub-tropical climates and has become a problem plant inareas of the southern USA, South America, East,West and Southern Africa, South and South EastAsia and Australia. Its spread throughout the worldhas taken place over the last 100 years or so,although the actual course of its spread is poorlydocumented. In the last 10 years the rapid spread ofthe plant in many parts of Africa has led to plant is a perennial aquatic herb (Eichhorniacrassipes) which belongs to the family Pontedericeae,closely related to the Liliaceae (lily family). Themature plant consists of long, pendant roots,rhizomes, stolons, leaves, inflorescences and fruitclusters. The plants are up to 1 metre high although40cm is the more usual height. The inflorescencebears 6 - 10 lily-like flowers, each 4 - 7cm in diameter.

3 The stems and leaves contain air-filled tissue whichgive the plant its considerable buoyancy. Thevegetation reproduction is asexual and takes place ata rapid rate under preferential conditions. (Herfjord,Osthagen and Saelthun 1994).The problemWater HYACINTH can cause a variety of problems when its rapid mat-like proliferation coversareas of fresh WATER . Some of the common problems are listed below: Hindrance to WATER transport. Access to harbours and docking areas can be seriouslyhindered by mats of WATER HYACINTH . Canals and freshwater rivers can becomeimpassable as they clog up with densely intertwined carpets of the weed. It is alsobecoming a serious hazard to lake transport on Lake Victoria as large floating islands ofwater HYACINTH form, while many of the inland waterways of south east Asia have been allbut 1: WATER HYACINTH Paul CalvertWater HYACINTH Intermediate Technology Development Group2 Figure 2: WaterHyacinth causesproblems in manyregions Paul Calvert Clogging of intakes of irrigation, hydropower and WATER supply systems.

4 Many largehydropower schemes are suffering from the effects of WATER HYACINTH . The Owen Fallshydropower scheme at Jinja on Lake Victoria is a victim of the weeds rapid reproductionrates and an increasing amount of time and money is having to be invested in clearing theweed to prevent it entering the turbine and causing damage and power interruptions. WATER HYACINTH is now a major problem in some of the world s major dams - the Karibadam which straddles the Zambia-Zimbabwe border on the Zambezi River and feeds Hararehas pronounced infestations of the weed. Blockage of canals and rivers causing flooding. WATER HYACINTH can grow so densely thata human being can walk on it. When it takes hold in rivers and canals it can become sodense that it forms a herbivorous barrage and can cause damaging and dangerousflooding. Micro-habitat for a variety of disease vectors. The diseases associated with the presenceof aquatic weeds in tropical developing countries are among those that cause the majorpublic health problems: malaria, schistosomiasis and lymphatic filariasis.

5 Some speciesof mosquito larvae thrive on the environment created by the presence of aquatic weeds,while the link between schistosomiasis (bilharzia) and aquatic weed presence is wellknown. Although the statistical link is not well defined between the presence of aquaticweeds and malaria and schistosomiasis, it can be shown that the brughian type offilariasis (which is responsible for a minor share of lymphatic filariasis in South Asia) isentirely linked to the presence of aquatic weeds (Bos, 1996). Increased evapotranspiration. Various studies have been carried out to ascertain therelationship between aquatic plants and the rate of evapotranspiration compared withevaporation from an open-surfaced WATER body. Saelthun (1994) suggests that the rate ofwater loss due to evapotranspiration can be as much as times that of evaporation fromthe same surface but free of plants. This has great implications where WATER is alreadyscarce.

6 It is estimated that the flow of WATER in the Nile could be reduced by up to onetenth due to increased losses in Lake Victoria from WATER HYACINTH . Problems related to fishing. WATER HYACINTH can present many problems for thefisherman. Access to sites becomes difficult when weed infestation is present, loss offishing equipment often results when nets or lines become tangled in the root systems ofthe weed and the result of these problems is more often than not a reduction in catch andsubsequent loss of livelihood. In areas where fishermen eke a meagre living from theirtrade, this can present serious socio-economic problems. Fishermen on lake Victoriahave also noted that, in areas where there is much WATER HYACINTH infestation, the WATER is still and warm and the fish disappear . They also complain that crocodiles and snakesWater HYACINTH Intermediate Technology Development Group3have become more prevalent.

7 Reduction of biodiversity. Where WATER HYACINTH is prolific, other aquatic plants havedifficulty in surviving. This causes an imbalance in the aquatic micro-ecosystem and oftenmeans that a range of fauna that relies on a diversity of plant life for its existence, willbecome extinct. Diversity of fish stocks is often effected with some benefiting and otherssuffering from the proliferation of WATER HYACINTH . People often complain of localised waterquality deterioration. This is of considerable concern where people come to collect waterand to of the problem is often extremely difficult. The real effect on fish stocks and flora isunknown. It is hard to calculate the effect on fishing communities. Even quantifying the coverageof the weed is difficult on bodies of WATER which are as large and geographically complex as LakeVictoria. Satellite methods are the only accurate way of determining the spread of the weed.

8 Success is hard to measure when the exact scale of the problem is not clearly defined and isanyway growing many areas of the world fewstudies have been carried out toquantify the basic effects of thegrowth of the weed on thesurrounding communities andenvironment. This causesproblems when trying toevaluate the scale of theproblem, POSSIBLE ways ofcombating its proliferation andthe impact that any CONTROL ormanagement programme 3: The scale of the problem is considerable Paul CalvertSolutionsControl of WATER hyacinthThere are several popular CONTROL mechanisms for preventing the spread of, or eradication of, waterhyacinth. The 3 main mechanisms used are biological, chemical and physical CONTROL . Each hasits benefits and drawbacks. Chemical CONTROL is the least favoured due the unknown long-termeffects on the environment and the communities with which it comes into contact. Physicalcontrol, using mechanical mowers, dredgers or manual extraction methods, is used widely but iscostly and cannot deal with very large infestations.

9 It is not suitable for large infestations and isgenerally regarded as a short-term solution. Biological CONTROL is the most widely favoured long-term CONTROL method, being relatively easy to use, and arguably providing the only economic andsustainable CONTROL . Below we will briefly discuss each of these controlBiological CONTROL is the use of host specific natural enemies to reduce the population density of apest. Several insects and fungi have been identified as CONTROL agents for WATER HYACINTH . Theseinclude a variety of weevils, moth and fungi. Biological CONTROL of WATER HYACINTH is said to beenvironmentally benign as the CONTROL agents tend to be self-regulating. CONTROL programmes areWater HYACINTH Intermediate Technology Development Group4usually inexpensive due to the fact that the CONTROL agents are known and only a small numbers ofstaff are required to run such programmes. One major drawback is that it can take a long time toinitiate such projects because it can take several years for the insect population to reach apopulation density sufficient to tackle the pest Kenya work is being carried out on the development of a biological herbicide from a locally foundfungal controlThe application of herbicides for controlling WATER HYACINTH has been carried out for many years.

10 The common herbicides are 2,4-d, Diquat and Glysophate. It has been found that there is a goodsuccess rate when dealing with small infestations but less success with larger areas. Applicationcan be from the ground or from the air and requires skilled operators. As mentioned earlier themain concern when using herbicides is the environmental and health related effects, especiallywhere people collect WATER for drinking and controlMechanical removal of WATER HYACINTH is seen as the best short-term solution to the proliferation ofthe plant. It is however costly, using either land-based clamshell bucket cranes, draglines orbooms or, alternatively, WATER based machinery such as mowers, dredges, barges or speciallydesigned aquatic weed harvesters. Such methods are suitable for only relatively small of these techniques require the support of a fleet of WATER and land-based vehicles fortransporting the large quantities of WATER HYACINTH which is removed.