Water hyacinth (Eichhornia crassipes) is a fast-growing flowering plant species with ovular, waxy leaves. Water hyacinth is listed as a federal noxious weed in the United States. This species is invasive to ponds, lakes, rivers and other wetland habitats. It forms dense, floating mats of vegetation that restricts light to underwater environments.
I. Appearance and Characteristics
Pontederia crassipes (formerly Eichhornia crassipes), commonly known as common water hyacinth, is an aquatic plant native to South America, naturalized throughout the world, and often invasive outside its native range. It is the sole species of the subgenus Oshunae within the genus Pontederia. Anecdotally, it is known as the “terror of Bengal” due to its invasive growth tendencies.
Water hyacinth is a free-floating perennial aquatic plant (or hydrophyte) native to tropical and subtropical South America. With broad, thick, glossy, ovate leaves, water hyacinth may rise above the surface of the water as much as 1 m (3 ft) in height. The leaves are 10–20 cm (4–8 inches) across on a stem, which is floating by means of buoyant bulb-like nodules at its base above the water surface. They have long, spongy, bulbous stalks. The feathery, freely hanging roots are purple-black. An erect stalk supports a single spike of 8–15 conspicuously attractive flowers, mostly lavender to pink in colour with six petals. When not in bloom, water hyacinth may be mistaken for frogbit (Limnobium spongia) or Amazon frogbit (Limnobium laevigatum).
One of the fastest-growing plants known, water hyacinth reproduces primarily by way of runners or stolons, which eventually form daughter plants. Each plant additionally can produce thousands of seeds each year, and these seeds can remain viable for more than 28 years. Common water hyacinths are vigorous growers, and mats can double in size in one to two weeks. In terms of plant count rather than size, they are said to multiply by more than a hundredfold in number in a matter of 23 days.
In their native range, the flowers are pollinated by long-tongued bees, and the plants can reproduce both sexually and clonally. The invasiveness of the hyacinth is related to its ability to clone itself, and large patches are likely to all be part of the same genetic form.
Water hyacinth has three flower morphs and is termed “tristylous”. The flower morphs are named for the length of their pistils: long (L), medium (M), and short (S). Tristylous populations are, however, limited to the native lowland South American range of water hyacinth; in the introduced range, the M-morph prevails, with the L-morph occurring occasionally and the S-morph is absent altogether. This geographical distribution of the floral morphs indicates that founder events have played a prominent role in the species’ worldwide spread.
Its habitat ranges from tropical desert to subtropical or warm, temperate desert to rainforest zones. The temperature tolerance of the water hyacinth is:
- Its minimum growth temperature is 12 °C (54 °F)
- Its optimum growth temperature is 25–30 °C (77–86 °F)
- Its maximum growth temperature is 33–35 °C (91–95 °F)
Its pH tolerance is estimated at 5.0–7.5. Leaves are killed by frost and plants do not tolerate water temperatures more than 34 °C (93 °F). Water hyacinths do not grow where the average salinity is greater than 15% that of sea water (around 5 g salt per kg). In brackish water, its leaves show epinasty and chlorosis, and eventually die. Rafts of harvested water hyacinth have been floated to the sea, which kills it.
Azotobacter chroococcum, a species of nitrogen-fixing bacteria, is probably concentrated around the bases of the petioles, but the bacteria do not fix nitrogen unless the plant is suffering extreme nitrogen deficiency.
Fresh plants contain prickly crystals. This plant is reported to contain hydrogen cyanide, alkaloids, and triterpenoids, and may induce itching. Plants sprayed with 2,4-dichlorophenoxyacetic acid (2,4-D) may accumulate lethal doses of nitrates and other harmful elements in polluted environments.
II. How to Grow and Care
Watering
Thriving in its native tropical habitats, water hyacinth has adapted to flourish with high humidity and frequent water contact. This species is highly water-loving, displaying a preference for consistent moisture without being drought-tolerant. Care should include watering every week to maintain its lush growth. As an aquatic plant often grown outdoors, water hyacinth benefits from the natural ebb and flow of rain cycles, which helps regulate its growth and flowering phases according to seasonal water availability.
Propagation
The ideal time to propagate water hyacinth tends to be during Spring and Summer seasons. Favor the Cutting method for efficient propagation. Success can be observed through new leaf growth and root development. Maintain optimal hydration to ensure successful propagation.
Transplanting
Optimal transplanting for water hyacinth coincides with the mid to late summer warmth. Choose sunny spots with abundant water. If necessary, gently handle and ensure minimal root disturbance for a seamless transition.
III. Uses and Benefits
Bioenergy
Because of its extremely high rate of development, Pontederia crassipes is an excellent source of biomass. One hectare (2.5 acres) of standing crop thus produces more than 70,000 m3/ha (1,000,000 cu ft/acre) of biogas (70% , 30% ). According to Curtis and Duke, one kg (2.2 lb) of dry matter can yield 370 litres (13 cu ft) of biogas, giving a heating value of 22,000 kJ/m3 (590 Btu/cu ft) compared to pure methane (895 Btu/ft3)
Wolverton and McDonald report approximately 0.2 m3/kg (3 cu ft/lb) methane, indicating biomass requirements of 350 t/ha (160 short ton/acre) to attain the 70,000 m3/ha (1,000,000 cu ft/acre) yield projected by the National Academy of Sciences (Washington). Ueki and Kobayashi mention more than 200 t/ha (90 short ton/acre) per year. Reddy and Tucker found an experimental maximum of more than 1⁄2 tonne per hectare (1⁄4 short ton/acre) per day.
Bengali farmers collect and pile up these plants to dry at the onset of the cold season; they then use the dry water hyacinths as fuel. The ashes are used as fertilizer. In India, one tonne (1.1 short tons) of dried water hyacinth yields about 50 liters ethanol and 200 kg residual fiber (7,700 Btu). Bacterial fermentation of one tonne (1.1 short tons) yields 26,500 ft3 gas (600 Btu) with 51.6% methane (), 25.4% hydrogen (), 22.1% carbon dioxide (), and 1.2% oxygen (). Gasification of one tonne (1.1 short tons) dry matter by air and steam at high temperatures (800 °C or 1,500 °F) gives about 40,000 ft3 (1,100 m3) natural gas (143 Btu/ft3) containing 16.6% , 4.8% , 21.7% (carbon monoxide), 4.1% , and 52.8% (nitrogen). The high moisture content of water hyacinth, adding so much to handling costs, tends to limit commercial ventures. A continuous, hydraulic production system could be designed, which would provide a better utilization of capital investments than in conventional agriculture, which is essentially a batch operation.
The labor involved in harvesting water hyacinth can be greatly reduced by locating collection sites and processors on impoundments that take advantage of prevailing winds. Wastewater treatment systems could also favorably be added to this operation. The harvested biomass would then be converted to ethanol, biogas, hydrogen, gaseous nitrogen, and/or fertilizer. The byproduct water can be used to irrigate nearby cropland.
Phytoremediation, wastewater treatment
Water hyacinth removes arsenic from arsenic-contaminated drinking water. It may be a useful tool in removing arsenic from tube well water in Bangladesh.
Water hyacinth is also observed to enhance nitrification in wastewater treatment cells of living technology. Their root zones are superb micro-sites for bacterial communities.
Water hyacinth is a common fodder plant in the third world especially Africa though excessive use can be toxic. It is high in protein (nitrogen) and trace minerals and the goat feces are a good source of fertilizer as well.
Water hyacinth is reported for its efficiency to remove about 60–80% nitrogen and about 69% of potassium from water. The roots of water hyacinth were found to remove particulate matter and nitrogen in a natural shallow eutrophicated wetland.
The plant is extremely tolerant of, and has a high capacity for, the uptake of heavy metals, including cadmium, chromium, cobalt, nickel, lead, and mercury, which could make it suitable for the biocleaning of industrial wastewater.
The roots of Pontederia crassipes naturally absorb some organic compounds believed to be carcinogenic, in concentrations 10,000 times that in the surrounding water. Water hyacinths can be cultivated for waste water treatment (especially dairy waste water).
In addition to heavy metals, Pontederia crassipes can also remove other toxins, such as cyanide, which is environmentally beneficial in areas that have endured gold-mining operations.
Water hyacinth can take in and degrade ethion, a phosphorus pesticide.
Agriculture
In places where water hyacinth is invasive, overabundant, and in need of clearing away, these traits make it free for the harvesting, which makes it very useful as a source of organic matter for composting in organic farming. It is used internationally for fertilizer and as animal feed and silage for cattle, sheep, geese, pigs, and other livestock.
In Bengal, India the kachuri-pana has been used primarily for fertilizer, compost or mulch, and secondarily as fodder for livestock and fish. In Bangladesh, farmers in the southwestern region cultivate vegetables on “floating gardens” usually with a bamboo-built frame base, with dried mass of water hyacinth covered in soil as bedding. As a large portion of cultivable land goes under water for months during monsoon in this low-lying region, farmers have grown this method for many decades now. The method of this agriculture is known by many names including dhap chash and vasoman chash.
In Kenya, East Africa, it has been used experimentally as organic fertilizer, although there is controversy stemming from the high alkaline pH value of the fertilizer.
Other uses
In various places in the world, the plant is used for making furniture, handbags, baskets, rope, and household goods/interior products (lampshades, picture frames) by businesses launched by NGOs and entrepreneurs.
- Woven products
American-Nigerian Achenyo Idachaba has won an award for showing how this plant can be exploited for profit as woven procuts in Nigeria.
- Paper
Though a study found water hyacinths of very limited use for paper production, they are nonetheless being used for paper production on a small scale. Goswami pointed out in his article that water hyacinth has the potential to make tough and strong paper. He found that adding water hyacinth pulp to the raw material of bamboo pulp for anti-grease paper can increase the physical strength of paper.
- Edibility
The plant is used as a carotene-rich table vegetable in Taiwan. Javanese sometimes cook and eat the green parts and inflorescence. Vietnamese also cook the plant and sometimes add its young leaves and flower to their salads.
- Medicinal use
In Kedah (Malaysia), the flowers are used for medicating the skin of horses. The species is a “tonic”.
- Potential as bioherbicidal agent
Water hyacinth leaf extract has been shown to exhibit phytotoxicity against another invasive weed Mimosa pigra. The extract inhibited the germination of M. pigra seeds in addition to suppressing the root growth of the seedlings. Biochemical data suggested that the inhibitory effects may be mediated by enhanced hydrogen peroxide production, inhibition of soluble peroxidase activity, and stimulation of cell wall-bound peroxidase activity in the root tissues of M. pigra.
IV. How to Control
Control depends on the specific conditions of each affected location such as the extent of water hyacinth infestation, regional climate, and proximity to human and wildlife.
Chemical control
Chemical control is the least used of the three controls of water hyacinth, because of its long-term effects on the environment and human health. The use of herbicides requires strict approval from governmental protection agencies and skilled technicians to handle and spray the affected areas. The use of chemical herbicides is only used in case of severe infiltration of water hyacinth.
However, the most successful use of herbicides is when it is used for smaller areas of infestation, because in larger areas, more mats of water hyacinths are likely to survive the herbicides and can fragment to further propagate a large area of water hyacinth mats. In addition, it is more cost-effective and less laborious than mechanical control, yet it can lead to environmental effects, as it can penetrate into the groundwater system and can affect not only the hydrological cycle within an ecosystem, but also negatively affect the local water system and human health. Also of note, the use of herbicides is not strictly selective of water hyacinths; keystone species and vital organisms such as microalgae can perish from the toxins and can disrupt fragile food webs.
The chemical regulation of water hyacinths can be done using common herbicides such as 2,4-D, glyphosate, and diquat. The herbicides are sprayed on the water hyacinth leaves and lead to direct changes to the physiology of the plant. The use of the herbicide known as 2,4-D leads to the death of water hyacinth through inhibition of cell growth of new tissue and cellular apoptosis. Almost a two-week period may be needed before mats of water hyacinth are destroyed with 2, 4-D. Between 75,000 and 150,000 acres (30,000 and 61,000 ha) of water hyacinth and alligator weed are treated annually in Louisiana.
The herbicide known as diquat is a liquid bromide salt that can rapidly penetrate the leaves of the water hyacinth and lead to immediate inactivity of plant cells and cellular processes. The herbicide glyphosate has a lower toxicity than the other herbicides, so takes longer for the water hyacinth mats to be destroyed (about three weeks). The symptoms include steady wilting of the plants and a yellow discoloration of the plant leaves that eventually leads to plant decay.
Physical control
Physical control is performed by land-based machines, such as bucket cranes, draglines, or boom, or by water-based machinery such as aquatic weed harvesters, dredges, or vegetation shredders. Mechanical removal is seen as the best short-term solution to the proliferation of the plant.
A project on Lake Victoria in Africa used various pieces of equipment to chop, collect, and dispose of 1,500 hectares (3,700 acres) of water hyacinth in a 12-month period. It is, however, costly and requires the use of both land and water vehicles, but many years were needed for the lake to become in poor condition, and reclamation will be a continual process.
It can have an annual cost from $6 million to $20 million and is only considered a short-term solution to a long-term problem. Another disadvantage with mechanical harvesting is that it can lead to further fragmentation of water hyacinths when the plants are broken up by spinning cutters of the plant-harvesting machinery. The fragments of water hyacinth that are left behind in the water can easily reproduce asexually and cause another infestation.
Transportation and disposal of the harvested water hyacinth is a challenge, though, because the vegetation is heavy in weight. The harvested water hyacinth can pose a health risk to humans because of the plant’s propensity for absorbing contaminants, and it is considered toxic to humans. Furthermore, the practice of mechanical harvesting is not effective in large-scale infestations, because this aquatic invasive species grows much more rapidly than it can be eliminated. Only one to two acres (1⁄2 to 1 ha) of water hyacinth can be mechanically harvested daily because of the vast amounts in the environment. Therefore, the process is very time-intensive.
Biological control
As chemical and mechanical removals are often too expensive, polluting, and ineffective, researchers have turned to biological control agents to deal with water hyacinth. The effort began in the 1970s, when USDA researchers released into the United States three species of weevils known to feed on water hyacinth, Neochetina bruchi, N. eichhorniae, and the water hyacinth borer Sameodes albiguttalis. The weevil species were introduced into the Gulf Coast states, such as Louisiana, Texas, and Florida, where thousands of acres were infested by water hyacinth.
A decade later, a decrease was found in water hyacinth mats by as much as 33%, but because the lifecycle of the weevils is 90 days, the use of biological predation to efficiently suppress water hyacinth growth is limited. These organisms regulate water hyacinth by limiting its size, vegetative propagation, and seed production. They also carry microorganisms that can be pathological to the water hyacinth. These weevils eat stem tissue, which results in a loss of buoyancy for the plant, which will eventually sink. Although meeting with limited success, the weevils have since been released in many other countries. However, the most effective control method remains the control of excessive nutrients and prevention of the spread of this species.
In May 2010, the USDA’s Agricultural Research Service released Megamelus scutellaris as an additional biological control insect for the invasive water hyacinth species. M. scutellaris is a small planthopper insect native to Argentina. Researchers have been studying the effects of the biological control agent in extensive host-range studies since 2006 and concluded that the insect is highly host-specific and will not pose a threat to any other plant population other than the targeted water hyacinth. Researchers also hope that this biological control will be more resilient than existing biological controls and the herbicides that are already in place to combat the invasive water hyacinth. Another insect being considered as a biological control agent is the semiaquatic grasshopper Cornops aquaticum. This insect is specific to the water hyacinth and its family, and besides feeding on the plant, it introduces a secondary pathogenic infestation. This grasshopper has been introduced into South Africa in controlled trials.
The Rhodes University Centre for Biological Control is rearing M. scutellaris and the water hyacinth weevils N. eichhorniae and N. bruchi en masse for biological control at dams in South Africa, including the Hartbeespoort Dam. The moth Niphograpta albiguttalis (Warren) (Lepidoptera: Pyralidae) has been introduced to North America, Africa, and Australia. Larvae of this moth bore in the stems and flower buds of water hyacinth.