The increased proliferation of water hyacinth in different water bodies across Zimbabwe has become a grim reality of the dangers of invasive alien species. Unprecedented growth of water hyacinth in water bodies over the years, entails urgent action to curb the problem, which is fast becoming an issue of national importance. Uncontrolled disposal of effluent, sewage and urban agriculture in upper catchment activities has caused an increased nutrient load in water bodies. Water pollution remains by far the leading factor responsible for promoting the growth of this unwanted water weed. Failure to deal with water hyacinth could further affect water quality, cause fish death, increase costs of water treatment and reduce the aesthetic use of the environment. Analysis of water hyacinth in the last 40 years from 1980 to present indicates that the problem is worsening each and every day. Drastic measures are therefore required in order to control the colonization of water bodies by water hyacinth.
Water hyacinth, botanically known as Eichhornia crassipes, is considered the most notorious, free-floating alien weed that originated from the Amazon basin and Ecuador regions of Brazil, South America. The plant is non-native to the environment and it inhibits growth of many species. The proliferation of water hyacinth is becoming a problematic global phenomenon.
The introduction of water hyacinth across the tropical, subtropical, and warm temperate regions of Africa, Asia, Australia, Europe, and North America was through human activity. Humans introduced water hyacinth as an ornamental species to adorn inland water bodies. The large blue, purple and violet flowers of water hyacinth, along with their glossy leaves, and bulbous petioles attributed to the popularity of water hyacinth as an ornamental species. The International Union for the Conservation of Nature (IUCN) has identified water hyacinth as one of the top 10 invasive alien species in the world.
The spread of Eichhornia crassipes has triggered adverse ecological, economic and social impacts in warm tropical and sub-tropical countries globally. Firstly, water hyacinth affects the ability to abstract water from water bodies. It also adversely affects the ability to undertake social and recreational activities at the water bodies. Selected recreational activities include boat cruising and canoeing. Water hyacinth is denoted by its’ thick, broad, glossy leaves and its floating characteristics. At its peak, water hyacinth grows almost four feet off the water’s surface and extends below the water surface with purple feather-like roots.
Water Hyacinth as an invasive alien species, reproduces quickly and can rapidly cover the surface of a water body in very little time. Consequently, sunlight is prevented from penetrating through the water column, leading to the death of native aquatic plants. The death of these native plants leads to an influx of bacteria that consume the decaying plant matter. These bacteria deplete the dissolved oxygen and available resources leading to the death of fish, and other types of aquatic life. Ecological effects of water hyacinth include the loss of local aquatic biodiversity. Social impacts of water hyacinth infestation include the reduction in water recreational activities (swimming, fishing and boating)
In the year 1937, Zimbabwe recorded the first presence of water hyacinth and by the end of 1988, the infestation had expanded to include the Lake Chivero, Manyame Dam, Manyame river and its tributaries, Lake Mutirikwi, wetlands in Chinamora, Mutoko and Bindura as well as dams in Triangle. Even if the invasion has affected many water bodies, Lake Chivero is of great concern, since it is the main water reservoir supplying Harare.
Lake Chivero, formerly known as Lake McIlwaine, stood as the most affected waterbody as a result of the diminished water quality. The spread and rapid invasion of water hyacinth in Lake Chivero is largely exacerbated by high levels of eutrophication aggravated by nutrient-rich agricultural run-off, effluent from sewage and industrial manufacturing.
Due to high levels of contamination, an increased level of chemicals is required for water treatment. This is also associated with increased cost of water purification.
Efforts to mitigate the spread of water hyacinth started in 1956 when herbicides were used as a control measure. In 1986 manual removal of weeds was adopted following the concern of the possible undesirable effects caused by herbicides. However, this method had limited success because physical removal of weeds proved to be expensive. Instead of reducing the spread of the weed, the manual removal becomes an indirect way of spreading the weed. This is because the physical removal releases the offspring plants hence promoting its infestation.
Curbing the problem of water contamination in Lake Chivero could be done through the practice of Integrated Water Resource Management (IWRM), Resource Efficient and Cleaner Production (RECP), catchment management, enforcement of environmental laws, watershed management and public awareness.
Scientific research confirms that water hyacinth is spreading in the water bodies of Zimbabwe, hence the need to promote measures that improve water quality. Within the next 20 years it may be difficult to carry out a boat cruise in some of our water bodies and the treatment of water will become more costly due to the deadly effects of water hyacinth. Action should begin now.
