Water Hyacinth Ecological Value, Environmental Impacts

By Henrylito D. Tacio 

Laguna, 18 Aug 2009. It is a free-floating perennial aquatic plant native to tropical South America. With broad, thick, glossy, ovate leaves, it may rise above the surface of the water as much as one meter in height. The leaves are 10-20 centimeters across, and float above the water surface. It has long, spongy and 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 color with six petals. 

Experts call it water hyacinth but to most Filipinos it is known as “water lily.” Water hyacinth (scientific name: Eichornia crassipes) is considered the most productive plant on earth as it yields more than 200 tons of dry matter per hectare per year under normal conditions. On water containing high concentrations of sewage, it yields up to 657 tons of dry matter per hectare. 

“The plant is far more productive than the crops that have been carefully cultivated by man under near-ideal conditions of fertilization, irrigation, and pest control,” wrote John Bunton in an article which appeared in Far Eastern Agriculture. 

Water hyacinth was introduced into many parts of the world, including the Philippines, as an ornamental garden pond plant due to its beauty. But today, it is considered a pest as 10 plants could produce well over 650,000 offspring within eight months. 

In Laguna de Bay, for instance, water hyacinth is considered a nuisance. “These plants now cover some 20% of the lake's surface area,” said Edgardo Manda, general manager of Laguna Lake Development Authority. He added that such proliferation threatens survival of aquatic species there since these plants block sunlight’s penetration into the water. 

That is just one of its ecological impacts. Water hyacinth also reduces biological diversity, impacts native submersed plants, alters immersed plant communities by pushing away and crushing them, and also alter animal communities by blocking access to the water and/or eliminating plants the animals depend on for shelter and nesting. In Lake Victoria, African fishermen have 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 snakes have become more prevalent.  

The physical problems brought about by water hyacinth are now common knowledge. Water hyacinth mats clog waterways, making boating, fishing and almost all other water activities impossible. Many large hydropower schemes are suffering from the effects of water hyacinth. 

In the 1990s, the world reportedly spent US$3 billion a year just to control the weed, for the most part with little or no success. “Its phenomenal growth rate outstrips the systems employed,” Bunton claimed.

Currently, there are several popular control mechanisms for preventing the spread of or eradicating water hyacinth: biological, chemical and physical control. Each has its benefits and drawbacks. Chemical control is the least favored due the unknown long-term effects on the environment and the communities with which it comes into contact. Physical control, using mechanical mowers, dredgers or manual extraction methods, is used widely but is costly and cannot deal with very large infestations. It is not suitable for large infestations and is generally regarded as a short-term solution. Biological control is the most widely favored long- term control method, being relatively easy to use, and arguably providing the only economic and sustainable control.

In some parts of the world, researches have been done to make water hyacinth into a profitable crop instead of a serious pest. In Bangladesh, the Mennonite Central Committee has been experimenting with paper production from water hyacinth for some years. They have established two projects that make paper from water hyacinth stems. The water hyacinth fiber alone does not make a particularly good paper but when the fiber is blended with waste paper or jute the result is reportedly good.

Similar small-scale cottage industry papermaking projects have been successful in a number of countries, including the Philippines, Indonesia, and India.

Another application of water hyacinth is the production of rope. The fiber from the stems of the water hyacinth plant can be used to make rope. The stalk from the plant is shredded lengthways to expose the fibers and then left to dry for several days. The rope making process is similar to that of jute rope. The finished rope is treated with chemicals to prevent it from rotting. In Bangladesh, the rope is used by a local furniture manufacturer who winds the rope around a cane frame to produce an elegant finished product.  

In the Philippines, water hyacinth is dried and used to make baskets and matting for domestic use. The key to a good product is to ensure that the stalks are properly dried before being used. If the stalks still contain moisture then this can cause the product to rot quite quickly. In India, water hyacinth is also used to produce similar goods for the tourist industry. Traditional basket making and weaving skills are used.  

Charcoal briquetting is an idea which has been proposed in Kenya to deal with the rapidly expanding carpets of water hyacinth which are evident on many parts of Lake Victoria. The proposal is to develop a suitable technology for the briquetting of charcoal dust from the pyrolysis of water hyacinth. The project is still very much at the idea stage and both a technical and a socio-economic study are planned to evaluate the prospects for such a project.  

Water hyacinth can also be used to aid the process of water purification either for drinking water or for liquid effluent from sewage systems. In a drinking water treatment plant, water hyacinths have been used as part of the pretreatment purification step. In sewage systems, the root structures of water hyacinth (and other aquatic plants) provide a suitable environment for aerobic bacteria to function. Aerobic bacteria feed on nutrients and produce inorganic compounds which in turn provide food for the plants.

Using the water hyacinth as animal fodder is a traditional practice in many areas of Asia, including China, Bangladesh, Indonesia, India, Malaysia, the Philippines, and Thailand. In Malaysia, fresh water hyacinth is cooked with rice bran and fishmeal and mixed with copra meal as feed for pigs and ducks. However, it is suited to all animals as water hyacinth has high water and mineral content.

In China, it is common practice to mix water hyacinth in a pig swill containing a variety of other vegetable waste matter. The mix is boiled for hours until it is reduced to a mash. Coconut meal, fish meal and groundnut cake plus corn and rice bran, are often added to the mash.

5% of water hyacinth in the total diet of pigs leads to significantly weight gains. But feed containing 30 percent of more of hyacinth can reduce weight gain by over 90 percent. These tests show that water hyacinth as a feed for animals must be used with great care.

Water hyacinth is also a good feed for fish. For instance, 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 kilograms. It is an edible fish with a tasty white meat. It will eat submerged or floating plants and also bank grasses. The fish can be used for weed control and will eat up to 18-40 percent of its own body weight in a single day.

Other fish such as the tilapia, silver carp, and silver dollar fish are all aquatic and can be used to control aquatic weeds. Water hyacinth has also been used indirectly to feed fish. Dehydrated water hyacinth has been added to the diet of channel catfish fingerlings to increase their growth. It has also been noted that decay of water hyacinth after chemical control releases nutrients which promote the growth of phytoplankton with subsequent increases in fish yield.

Another agricultural use of water hyacinth is by turning them into green manure or as compost. As a green manure, it can be either ploughed into the ground or used as mulch. The plant is ideal for composting. After removing the plant from the water it can be left to dry for a few days before being mixed with ash, soil and some animal manure.

In Sri Lanka, water hyacinth is mixed with organic municipal waste, ash and soil, composted and sold to local farmers and market gardeners. In Bangladesh, farmers have started producing fertilizer made from water hyacinth.