Environmental Impact of hyacinth carpet on water bodies
Consultant, Environmental Sciences, 22, Pollisetti Enclave, Vikrampuri, Seccunderabad 500 009, A.P.
Water hyacinth (Eichhornia crassipes
(Mart) Solms is a troublesome aquatic weed and has spread in almost
all lakes, ponds and rivers not only in our country but in the
entire tropical world. Therefore attention has been focused on
its environmental impact since its luxuriant growth in the water
bodies interferes in the activities of mankind, which has caused
great concern. Its wide spread occurrence in the fresh water lakes
and riverbeds is proving detrimental to fishing, rowing, and depleting
water content from the water bodies and interfering in water utilization
and other activities. In view of the alarming situation, it was
decided to control the weed growth by utilizing the Biocontrol
methods to control the water hyacinth menace.
Water hyacinth by its abundance of leaves, dense vegetation and innumerable rootlets in tertiary manner obstruct water flow in irrigation channels, hydroelectric power generation, interfere with navigation, impedes flow of water and displaces many aquatic grasses which were useful as fodder for cattle and also suppresses the phytoplankton growth.
NEGATIVE EFFECTS OF THE WEED
-While water hyacinths have some positive impact; the weeds can be expensive nuisance in many ways:
-They can clog dam outflows and disrupt hydro-electric power generation intakes and irrigation canals.
-Interfere with water supply systems by blocking pipes pumping water from the dam, impair navigation, ie. the mat formed by the weeds cannot allow the smooth passage of canoes and engine powered boats,
-Curtail recreation activities such as swimming, boat cruise and other attractions.
-Damage fisheries by making it difficulty for some fishing methods such as fishing nets to be spread on water.
-Weeds also deplete aquatic biodiversity where some fish species either die or migrate while free breeding is also inhibited.
-The weed also changes water chemistry by reducing its levels of oxygen leading to suffocation and eventual death of other living organisms including fish. This phenomenon could have led to the disappearance of the Kafue bream.
-The weeds become breeding places for mosquitoes and other creatures like snakes, frogs and snails-hence, diseases like malaria, schistosomiasis, encephalitis, filariasis and cholera.
-excessive wastage of water through transpiration. The rates of loss can be up to 13 times that from a free water surface.
-Weeds can also reduce the speed and quantity of water flowing in the dam thereby increasing the possibilities of flooding.
POSITIVE EFFECTS OF THE WEED
On the positive side water hyacinths
can be used as water purifiers because of their capability to
absorb high levels of poisonous chemicals such as sulphides and
other heavy metals. In some countries the weed is used to build
wetlands or as animal feeds and manure for farmlands.
Water hyacinth plants have a tremendous growth and reproductive rate and the free-floating mats cause substantial problems. Millions of dollars are spent each year in the United States for its management. Water hyacinth has been widely distributed because of the beauty of its large, purple to violet flowers.
Water hyacinth has not been found in the wild in Washington, but it is sold as an ornamental plant in plant nurseries. Although it is thought that water hyacinth cannot survive Washington's winters, its presence as an ornamental makes it possible for escape and growth in the wild. Water hyacinth does survive freezing conditions in other states where it is established and it may be possible for this plant to survive western Washington's relatively warm winters.
Thick mats of water hyacinth cause complete depletion of dissolved oxygen, which is essential for fish, birds and other aquatic life. Water hyacinth provides suitable breeding places for mosquitoes and other disease-carrying insects by stagnating the water in ditches and shallow areas. The plants are also known to carry pathogens, which infect several crops. The plant cover provides obnoxious smell, colouring matter and suspended particulate matter in water. The rate of organic matter production by water hyacinth is so high that the dead organic matter accumulates in the water body. The floating mats serve as excellent habitats for rats. Wherever these mats touch farmland and crop fields, the rodents attack everything that they can eat and then move from field to field increasing the rodent menace.
Water hyacinth can form impenetrable mats of floating vegetation. It reproduces by seeds and by daughter plants, which form on rhizomes and produce dense plant beds. In one study, two plants produced 1,200 daughter plants in four months. Individual plants break off the mat and can be dispersed by wind and water currents. As many as 5,000 seeds can be produced by a single plant and these seeds are eaten and transported by waterfowl. Seedlings are common on mud banks exposed by low water levels.
Reference: This extract is from the monograph on Environmental Biology of water hyacinth written by Dr. Mrs Kaiser Jamil, Deputy- Director Indian Institute of Chemical Technology, Hyderabad.