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Feature Article Water body infested with water hyacinth (Photo by Dipanjan Ghosh) WATER HYACINTH Befriending the Noxious Weed DIPANJAN GHOSH It is high time we befriended the noxious water hyacinth rather than keeping it away. I T is blacklisted as a notorious aquatic weed in India and other tropical countries, and often designated as ‘Bengal terror’, ‘blue devil’, ‘invasive weed’, ‘noxious plant’, ‘plant pest’, ‘prohibited aquatic weed’ and so on. The target of such abusive nicknames, water hyacinth, is a dreaded waterweed often blamed for choking water bodies and creating problems for other aquatic plants and animal inhabitants. However, lately its role in environmental cleaning is being truly recognized. Water hyacinth or Eichhornia crassipes (Mart) Solms, belongs to the family Pontederiaceac. The genus ‘Eichhornia’ was named after J.A. Fr Eichhorn (1779-1856), a Prussian Minister of Education while the species ‘crassipes’ means ‘thick foot’ in Latin. This monocotyledonous floating herb completes its life cycle within one year in seasonal water bodies although it is a perennial under favourable conditions. Water hyacinth is found mainly in freshwater bodies ranging from small ponds and ditches to large lakes and rivers. The plant even pesters rice fields. Water hyacinth forms a sprawling expanse of green embellished with lilac to violet flowers on the water bodies. Its well-developed submerged fibrous roots are devoid of root caps. But root pockets, like loose thimbles, keep the root apex covered. A rather striking presence of blue anthocyanin pigment 46 in the root tips of Eichhornia is also noticed. Stoloniferous stem is short, unbranched and with swollen internodes enveloped by sheathing leaf bases. The leaves are simple, large, broadly ovate or cuneate, deep green, coriaceous and with spongy inflated petiole; the leaf blade is smooth and glossy due to a waxy surface. Eichhornia flowers generally in August–September in the tropics. As this plant is sensitive to cold and is unable to survive below 6.5 0 C, flowering also seems to be influenced by temperature. Flowers are bisexual, slightly irregular, with six-lobed perianth united below into a tube and free above. The upper most tepal is with yellow, blue-bordered central splotch. Male sex organ comprises three long and three short stamens. The female sex organ, on the other hand, comprises three carpels in united condition. After the flowering is over the inflorescence bends down and the fruits develop under the water. The fruit is a three-celled capsule containing many minute, ribbed seeds. Water hyacinth is a very charming flowering plant, aptly called Water hyacinth is an unstoppable plant colonizer that cannot be eradicated completely. SCIENCE REPORTER, December 2010 ‘Cinderella of the plant kingdom’. Brazil is considered to be the native land of this plant. Attracted by its beautiful flowers, water hyacinth later became naturalized by man in many warm areas of the world like Central and North America, Africa, Asia, Australia and New Zealand. It is believed to have been introduced in India during 1890 by the British colonials. With increasing popularity of water gardening and home ponds, water hyacinth is now sold by many western nurseries for its unusual appearance, attractive flowers and Spike of water hyacinth flower – ‘Cinderella of the plant kingdom’ (Photo by Dipanjan Ghosh) Feature Article Spongy petioles help water hyacinth to float (Photo by Dipanjan Ghosh) ability to remove nutrients from the water. However, escape from captivity is a very common feature of this invasive weed. Further more, the magical ability of propagation has enabled it to conquer huge expanses of water bodies throughout the tropics every year. Unpleasant Activity Water hyacinth is called the worst aquatic plant in the world. It imposes both physical and ecological problems and has economic impact also. Its mats clog waterways making boating, fishing and almost all other water activities impossible. The risk of flood increases when drainage is impaired. The choked water bodies increase the possibility of water borne diseases and become breeding grounds especially for mosquitoes, which spread malaria and encephalitis. Eichhornia infestation also prevents sunlight and oxygen from getting into the water. As a result fishes and other aquatic animals perish when water bodies are choked with this weed. The phytoplanktons or surface dwellers also die due to dearth of light. Water hyacinth alters immersed plant communities by pushing away and crushing them (an acre of this weed can weigh more than 200 tons) and/or eliminating native plants the animals depend on for shelter and nesting. Water hyacinth can also provide a cheap yet effective way of removing arsenic from drinking water. Multifarious root system of water hyacinth (Photo by Dipanjan Ghosh) Moreover, the huge quantity of Eichhornia with trapped silt and dust make the water bodies shallow, even forming small islands where reeds and even woody plants invade. Water hyacinth has a distressing impact on agriculture, particularly on rice cultivation. Farmers face enormous problems in rainy season, when irrigation water flushes in tonnes of water hyacinth into the field. Luxuriant growth of water hyacinth also hampers hydroelectric power generation. Bird sanctuaries and wetlands infested with Eichhornia face serious problem as birds avoid these silted up water bodies affecting the tourism business as well as causing ecological imbalance. The entire Eichhornia plant is highly adapted to an aquatic mode of life. Some adaptive features and their impacts are discussed below: a) Numerous fibrous roots with a small pocket at the tip are a special adaptation to balance in the water and also to absorb maximum nutrients. Such an efficient root system has made Eichhornia a broad-spectrum mitigator, showing tolerance as well as accumulation of a large number of metals together. b) The petioles become characteristically swollen and develop spongyness, which provides buoyancy to the plant. Smooth, shining and frequently wax-coated leaves of water hyacinth protect from chemical and physical injuries and also prevent the water clogging of stomata. Perhaps for this, water hyacinth is usually seen unharmed in water bodies filled with toxic substances. c) The prolific growth of Eichhornia is very much dependent on its vegetative reproduction, which mainly occurs either by stolon production or by budding. Sexual reproduction occurs rarely through seeds. d) The flowers remain open only for a day and wither away even if pollination has not taken place. Moreover, the flowers are mostly selfpollinated. Hence, neither a partner plant nor any pollinating agent is essential for completing the life cycle. e) Eichhornia is a very potent hydrophyte, showing resistance to diseases and a large number of pests. Such adaptability has empowered water hyacinth to occupy any type of fresh water habitats throughout the world. Any Benefits? The ever-increasing population of Eichhornia as well as its impact on the society has made it indubitably one of the most annoying weeds of the tropics. It costs much energy and money in controlling water hyacinth. Today humans are making every effort, even using remote sensing to survey and monitor this weed, ultimately realizing that the copious growth of Eichhornia can be restricted only through its utilization in various aspects. The water hyacinth may be a promising possibility for solving needs of animal feed. It contains most SCIENCE REPORTER, December 2010 47 Feature Article Removing the invasive water hyacinth of the essential nutrients for animal growth but making a palatable feed from them is not easy because of the high moisture. However, the plants can be converted into silage by placing chopped plants in a closed container and allowing them to undergo microbial fermentation for about a month. Such silage has been shown to be highly palatable to sheep and other animals. Chinese cultivate the water hyacinth in fish ponds as pig fodder. Water hyacinth is also used as a carotene-rich table vegetable in Formosa. Javanese sometimes cook and eat the green parts (young leaves and petioles) and the inflorescence. It is rich in proteins, containing important amino acids like cystine, Water hyacinth is a big problem 48 Water hyacinth is found mainly in freshwater bodies ranging from small ponds and ditches to large lakes and rivers. The plant even pesters rice fields. It is believed to stop the spread of infection. Fresh juice of water hyacinth is also used as a styptic. phenylalanine, tyrosine, threonine, lysine, leucine, isoleucine and with valine and methionine in traces. However, the plant is virtually tasteless and eating the plant, which is reported to contain hydrogen cyanide, alkaloid and triterpenoid, may induce itching. Also fresh plant contains prickly crystals. Cellulose is a complex carbohydrate consisting of 3,000 or more glucose units. Water hyacinth is rich in cellulose content that can be used as a renewable source of energy and for production of paper. Biogas or methane production from the microbial anaerobic decomposition of water hyacinth has been investigated. It has been calculated that one hectare of water hyacinth can produce enough biomass each day to generate between 90 and 180 mt of methane gas and at the same time 0.5 tonne of residue as fertilizer. Eichhornia can also be used for production of power alcohol. Water hyacinth also contains cellulase, an industrially important enzyme, in amounts sufficient for commercial exploitation. The enzyme serves various industrial purposes like breaking down of insoluble material of fruit pulp, improving the quality of cotton textiles and increasing the tensile strength of paper pulp. The animal feed industry uses cellulase to convert fibres present in waste sludge into sugars and improve the efficiency of anaerobic water treatment processes. The process of manufacture of cellulase from water hyacinth comprises drying of plants, crushing, inoculating with a spore SCIENCE REPORTER, December 2010 suspension of the fungus Trichoderma reesei, incubation, extraction of enzyme, its purification and spray drying. The residue left after fermentation is utilized as a soil fertilizer. The fibrous root system of water hyacinth provides nesting habitat for invertebrates and insects. Leaf blades and petiole are occasionally used by coots. Even watercourses pervaded with water hyacinth are the breeding grounds for various snakes. The plant is also good for mulching and effective in conserving soil moisture. Wilted water hyacinth, mixed with earth, cow dung and wood ashes in the Chinese compost fashion can yield useful compost in just two months. There is no known medicinal value of water hyacinth in the world. However, in certain states of India, tribals use water hyacinth as a remedy against goiter disease. It is believed to stop the spread of infection. Fresh juice of water hyacinth is also used as a styptic. It is one of the best first-aid remedies for minute injuries. However, all these medicinal properties of water hyacinth are not clinically tested though such ethnomedicinal uses may one day be considered as promising. Perhaps the most striking feature of water hyacinth is its ability to absorb various pollutants and toxic metals released into the surrounding water bodies. Presently, this plant is used for removal of many heavy metals like cadmium, copper, lead, mercury and nickel and some other materials such as excess nitrogen, organic carbon, etc., perturbing the aquatic environment. Besides, water hyacinth can also provide a cheap yet effective way of removing arsenic from drinking water. A powder is made from the dried roots of water hyacinth, which removes nearly all the arsenic from water sample. It is reported that within one hour of adding the powder to the water, the arsenic level dropped from 200 ppb (parts per billion) to below the WHO’s safety limit of 10 ppb. Water hyacinth is an unstoppable plant colonizer that cannot be eradicated completely. We can only minimize its population by utilizing it for our benefit. Mr Dipanjan Ghosh, Chotonilpur Pirtala, P.O. & Dist Burdwan-713103, West Bengal