Socio-economic Impact of Water Hyacinth on Freshwater Ecosystems

Water hyacinth, Eichhornia crassipes belonging in the family pontederiaceae is a wildly invasive plant species believed to be indigenous to South America. Left unchecked its growth has led to a myriad of problems in major fresh water ecosystems around the globe. It interferes with fishing and fish processing and also, interferes with domestic and irrigation uses of the lakes. Major disadvantages related with the water hyacinth include blocking of water ways, interference with navigation and irrigation channels among others. Socio-economic effects are effects brought about by factors that directly or indirectly affect the economy of a particular country thereby causing a ripple effect to the societal norms. Most of the world’s rivers are heavily polluted with a huge chunk of them running through developing countries. This is because these countries have an underdeveloped sewer system, hence draw untreated sewage into rivers, streams and lakes. As urban centers grow rapidly they are challenged by waste disposal problems resulting in water pollution. This largely results in the proliferation of water hyacinth in the polluted water ways as nutrients and temperatures are key determinants of water hyacinth growth and reproduction. Understanding and managing the biological invasion threats posed by water hyacinth is the correct step taken towards sustainable development of the ecosystem. This study henceforth sets out to assess the socioeconomic impacts of water hyacinth on lakes.

Introduction

Currently, water hyacinth threatens aquatic ecosystems and prevents the management and delivery of freshwater services in both developing and developed countries. Like any other phytoplankton hydrophytes, Eichhornia crassipes forms dense covers that reduce light penetration to submerged plants thus competing with other plants for sunlight often displacing other animals from their natural habitats, depletes oxygen in aquatic communities resulting in destruction of biodiversity and composition of invertebrate communities as a result causing a ripple effect in the fishing industry.

Water hyacinth has the ability of reproducing both asexually and sexually. With its seeds germinating roughly after six months as dry conditions promotes its germination, this makes it almost impossible to control (Ueki and Oki, 1979).

It has been recorded that water hyacinth has invaded over 50 countries globally and that its distribution might expand into high latitudes with temperature rise due to global warming.

Eichhornia crassipes grows uncontrollably in both tropical and subtropical water bodies as this is where nutrient concentration is usually too high due to deforestation, poor waste water treatment, agricultural run-off and release of untreated sewage into water bodies.

The socio economic impacts of water hyacinth depends on the extent of the invasion, uses of the impacted water body, control methods and the response to control efforts. Therefore, research that simultaneously monitor the effects of water hyacinth on multiple trophic-levels are required to enhance our understanding of the invasive species.

In Africa, it is the most widespread and damaging aquatic plant species. The economic impacts of the weed in seven African counties have been estimated to be between USD20-50 million every year (UNEP, 2006).

Socioeconomic effects of water hyacinth on fresh water ecosystems

The socio-economic effects of water hyacinth include, destruction of biodiversity hence affecting recreation and tourism sectors. Water hyacinth is challenging the ecological stability of fresh water bodies, outcompeting all other species growing in the vicinity, posing a threat to aquatic biodiversity. Despite suppressing the growth of native species and negatively affecting micro-organisms, water hyacinth prevents the rapid growth of phytoplankton under large mats and ultimately affecting fisheries.

Secondly it leads to oxygen depletion and reduces water quality that is being depended upon by the community. Large water hyacinth mats prevents the transfer of oxygen from the air to the water surface and decreases oxygen production by other plants and algae as less sunlight penetrates to the submerged plants for photosynthesis (Vilamagna and Murphy 2010). When the plant dies, and sinks to the bottom, the decomposing biomass depletes oxygen content. Oxygen levels can reach low concentrations for fish sensitive to such changes. Furthermore, low dissolved oxygen conditions catalyze the release of phosphorus from the sediments which in turn accelerates eutrophication and can lead to subsequent increase in water hyacinth and algal blooms. Death and decay of water hyacinth vegetation in large masses deteriorates water quality and the quality of portable water, and increases treatment costs for drinking water (Patel, 2012, Mironga et al., 2011).

Thirdly, they are also breeding grounds for diseases, mosquitoes and other disease vectors. Floating water hyacinth mats support organisms that are dangerous to humans, the ability of its mass of fibres, floating roots and partially submerged leaves and stems to reduce water currents increases breeding habitat for the malaria causing anopheles mosquito as evidence in Lake Victoria (Minakawa et al., 2008). Mansonioides mosquitoes which are vectors for the nematode causing lymphatic filariasis reproduces on this weed (Chandra et al., 2006). Snails serving as vectors for the parasite of schistosomiasis (bilharzia) reside in the tangled weedmat (Borokoni and Babalola, 2012). Water hyacinth has also been implicated in harboring vibrio cholera, the causative agent for cholera. Yearly, water hyacinth coverage on Kenyan section of the lakes was positively associated with the number of cholera cases reported in Nyanza province. Also 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.

Another socio-economic effect is the blockage of water ways hampering agriculture, fisheries, recreation and hydroelectric power generation. Water hyacinth often clogs water ways due to its rapid reproduction and propagation rate. The dense mats disrupt socioeconomic and subsistence activities i.e. restricted access to recreational water, fisheries and tourism sites if waterways are blocked or water pipes clogged.

The floating mats may limit access to breeding nurseries and feeding grounds for some economically important fish species. In Lake Victoria, fish catch rate on the Kenyan section decreased by 45% because water hyacinth mats blocked access to fishing grounds, delayed access to markets and increased cost i.e. efforts and materials of fishing (Kataregga and Sterner, 2009).

In the Wouri River basin in Cameroon the livelihood of close to 9000inhabitans has been distorted- the entire Abo and Moundja Moussadi creeks have been rendered impassable by the weed leading to a complete alt in all the socio-economic activities with consequent rural exodus(Mujingni, 2012)

While navigation in the Bramaputra River in India has been affected by the wind, it has also blocked irrigation channels and obstructed the flow of water to crop fields, (Patel 2012). For example in west Bengal, it causes an annual loss in paddy by directly surprising the crop, inhibiting rice generation and interfering with harvest (EEA, 2012). The dense entangles with boat propellers, hampering fishing. Water hyacinth slows water flow by 40-95% in irrigation channels (Jons, 2009). Which may cause severe flooding. The communities of Bwene and Bonjo in the Wouri river basin in Cameroon regularly suffer from floods during the rainy season due to blockage of water ways around the villages by the weed (Mujingni, 2012).

It is estimated that the flow of water in Nile could be reduced by up to one-tenth due to increase losses from evapotranspiration by water hyacinth in Lake Victoria (Ndimele et al., 2011). Water loss by the same process and blocking of turbines on Kafue gorge in Zambia translates into most water for power generation and eventually into lost revenues of up to USD 15 million every year for the power company (ZEO, 2008).

Many large hydropower schemes are also suffering the effect of water hyacinth. For example cleaning intake screens at the Owen falls hydroelectric power plant at ginger in Uganda were calculated to be USD 1 million per year (Mailu, 2001).

Other socio-economic effects include, reduction of the area available for water birds, reduction in the number of fish species depended upon by the surrounding community and creates a micro climate by increasing evapotranspirative water loss, and it also leads to wastage of resources, cause lack of employment opportunities or job loss for the surrounding communities. It also disrupts hydroelectric power generation. Lack of access to debris free water, reduced access to water points and clogging of irrigation pipes. Water hyacinth mats increase flooding in rivers and canals by forming dams.

Control measures and management of water hyacinth

Eichhornia crassipes control is absolutely essential to the economy of a country. Control methods often used are mechanical, chemical and biological control. However existing methods have been insufficient to contain the aggressing growth of the weed and viability of its seeds despite substantial monetary investments over the years, mainly due to lack of continued policy and management support by government.

Manual and mechanical control

Physical methods for control of water hyacinth involve drainage of water body, manual removal of the weed or pulling through nets,. Employing machines like weed harvesters, crusher boats and destruction boats prove expensive, approximately USD 600- 1200 per acre (Malika, 2007, Vilamanga and Murphy, 2010). As well as undramatic for areas larger than an acre given the rapid rates of increase of the weed.

There may also be additional fees for disposal of plant materials which may prove expensive for the involved firm or government. In Europe management cost to remove 200 000 tons of the plant along 75km in the Guadiana river basin in the Portuguese-Spanish border amounted to EUR 14 680 between 2005 and 2008 (EEA, 2012). Yet while mechanical removal has been effective t a considerable extent, the infestation soon return because shredded branches of the weed are carried by the waves to other unaffected areas where they establish and start multiplying.

Chemical control

A generally cheaper method has been used worldwide to reduce water hyacinth population through the use of chemical herbicides eg paraquat, diquat, glyphosate, amitrole and 2, 4-D acid. However, their use directly interferes with the bio control agents currently deployed against this weed. Long-term use may degrade water quality and put aquatic life at risk with significant social economic impacts if beneficial or designated uses of the water bodies such drinking and preparing food are affected.

Considering that hundreds of thousands of hectares has been invaded by the weed, it is unlikely that it will be controlled by chemical means alone.

Biological control

Recently, focus has turned to natural enemies of water hyacinths including plant pathogens. The aim of any biological control is not to eradicate the weed but to reduce its abundance to a level where by it is no longer problematic.

While there exists several native enemies of water hyacinths, two South American weevil-beetles Neochetina eichhorniae and Neochetina bruchi. And two water hyacinth moth species Nephograpta albiguttalis and Xubida infusella have had effective control of water hyacinth in many countries notably at Lake Chivero at Zimbabwe, Lake Victoria Kenya, Louissina USA, Mexico, Pappua, New Guinea and Benin (Wiliam et al,. 2007, Venter et al,. 2012, Gichuki et al,. 2012).

Research has led to the discovery of another tiny insect Megamelus scutellaris, from South America which is highly host-specific to water hyacinth and does not pose danger to native or economically important species (Coetzee et al., 2009).

The weevils decrease water hyacinth growth rate by reducing plant size, flower and seed production. They also facilitate the transfer and ingress of deleterious microorganisms associated with the weevils i.e. both fungi and bacteria into the plant tissues.

Control of water hyacinths using fungal pathogens has greatly stimulated interests in the management of the weed. Several fungal species among them Cercospora rhodomanii, Alternaria alternate and Aeichhorniae are recognized as potential mycoherbicides agents although no commercial mycoherbisides is available for water hyacinth (Dagno et al., 2012)

Solutions and recommendations to curb the negative impacts of Eichhornia crassipes on the aquatic ecosystem

Over the last few decades, research into the adoption and related technologies for the control of water hyacinth have been tried. The biomass can be used in waste water treatment, heavy metal and dye remediation, as substrate for bio-ethanol and biogas production, electricity generation, industrial uses, manufacture of medicines, animal feeds, agriculture and sustainable development.

Waste water treatment and clean-up of polluted environment

There is potential to clean up contaminated waters by water hyacinth. It can be used to treat waste water from dairies, tanneries, sugar factories, pulp and paper industries, distilleries and etc.

The plant can absorb into its tissues large quantities of heavy metals from the water column and grows very well in water polluted with organic contaminants and high concentration of plant nutrients. While water hyacinth’s capacity to absorb nutrients makes it a potential biological alternative for treatment of agro-industrial waste water. One of the major challenges is how to properly dispose-off the vast amount of the plant materials which may have to be considered a toxic waste.

As alternative fuel energy source

Water hyacinth fulfils all the criteria deemed necessary for bio energy production. It is yearly, readily available, biodegradable and with high fibre content. However its strong disadvantage is that it has over 90% water that complicate harvesting and processing. The biomass can be subjected to biogas production to generate energy for house hold uses in rural area.

Experiments in china show that mixing biomass of water hyacinth with pig manure leads a much higher biomass production than by using pig manure alone. It can also be used for ethanol production. But technical and logistical challenges need to be overcome before the commercial scale of ethanol productions become a reality because of the high tissues water content.

Semi-industrial uses and house hold articles

As a readily available resource, water hyacinth has been used in several small industries, in the Philippines, Indonesia, India and Kenya for paper rope, baskets, mats, shoes, sandals, bags, vases and wallets. Yet these are rarely successful to reduce infestations and the market for this products is far too small to have any impact on water hyacinth populations. In addition, increased market demand may aid its spread to novel uninvaded waters.

Animal feedstock and agricultural use

When sundried, water hyacinth has been found to be rich in proteins, vitamins and minerals and serve as a high quality feedstock for some non-ruminant animals, poultry and fishery in Indonesia, China, Philippines and Thailand. (Lu et al., 2010). But it isn’t recommended for use if primarily used for removal of heavy metals from waste water.

Conclusion

However seldom does utilization provide a sustainable solution to the spread and impact of water hyacinth, and in fact could provide a perverse incentive to maintain the invasive plant to the destruction of the ecosystem. There is no one example from anywhere in the world where utilization alone has contributed to the management of any invasive plant.

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