Water hyacinth

The water hyacinth (Eichhornia crassipes ) is an aquatic plant commonly found in the southern United States, including Florida, Texas, the Gulf Coast, and California. As an introduced species , it has spread rapidly and is now viewed as
a noxious weed. Like other aquatic weeds, water hyacinth can grow rapidly and clog waterways, damaging underwater equipment and impairing navigational and recreational facilities. It is also viewed as a weed in many tropical parts of the world.

Water hyacinths can be either free-floating or rooted, depending on the depth of the water. The plant height may vary from a few inches to 3 ft (0.9 m). The leaves, growing in rosettes, are glossy green and may be up to 8 in (20 cm) long and 6 in (15 cm) wide. The showy, attractive flowers may be blue, violet, or white and grow in spikes of several flowers. The leaf blades are inflated with air sacs, which enable the plants to float in water. The seeds are very longlived. Studies show that seeds that have been buried in mud for many years remain viable under the right conditions, leading to reinfestation of lakes long after chemical treatment.

Weed harvesting methods to control water hyacinth growth are expensive and not very effective. The weight and volume of the harvested material usually adds greatly to the costs of hauling and disposal. Attempts to use the harvested material as soil fertilizer or enhancer have failed because of the low mineral and nutritive content of the plant's tissue. Chemical methods to control water hyacinth usually require careful and repeated applications. Commonly used herbicides include Rodeo and Diquat.

In some situations, aquatic weeds serve beneficial purposes. Aquatic plants can be integral components of wastewater treatment, particularly in warm climates. Wastewater is routed through lagoons or ponds with dense growths of water hyacinth. In waters containing excess nutrients (nitrates and phosphates ) and turbidity, water hyacinth plants have been shown to improve water quality by taking up the excess nutrients into the plant and by settling the suspended solids which cause turbidity. They also add oxygen to the water through photosynthesis . Oxygen is an essential requirement for the decomposition of wastewater, and oxygen deficiency is a common problem in waste treatment systems. Water hyacinth has been used successfully in California and Florida, and more states are exploring the possibility of using water hyacinth in waste treatment systems.

[Usha Vedagiri ]

RESOURCES

BOOKS

Hammer, Donald A. Constructed Wetlands for Waste Treatment. Chelsea, MI: Lewis Publishers, Inc., 1989.

Schmidt, James C. How to Identify and Control Water Weeds and Algae. Milwaukee: Applied Biochemists, Inc., 1987.