THE STUDY OF A SPECIOUS INVASIVE PLANT, WATER HYACINTH (EICHHORNIA CRASSIPES): ACHIEVEMENTS AND CHALLENGES

Abstract

Water hyacinth (Eichhornia crassipes) originated in the state of Amazonas, Brazil, spread to other regions of South America, and was carried by humans throughout the tropics and sub_tropics. It is now widespread and recognized as one of the top ten weeds in the world. Water hyacinth has invaded Africa, Asia, North America and Oceania, occurs in at least 62 countries and causes extremely serious ecological, economic and social problems in regions between 40°N and 45°S. Water hyacinth forms dense monocultures and can threaten local native communities, reduce native species diversity, and change the physical and chemical aquatic environment, thus altering ecosystem structure and function by disrupting food chains and nutrient cycling. Water hyacinth has had a great impact on local economic development. The large, dense monoculture formed by this species covers lakes and rivers, thus blocking waterways and interfering with the water transport of agriculture products, tourism activities, water power and irrigation of agricultural fields. Dense mats of water hyacinth can lower dissolved oxygen levels in water bodies and reduce aquatic production, including fish production, thereby reducing fish catches. Annual global costs associated with water hyacinth have increased greatly in recent years. Also, the lifestyles of local people who use and depend on water bodies invaded by water hyacinth have been affected greatly. Water hyacinth is very efficient at taking up calcium, magnesium, sulfur, iron, manganese, aluminum, boron, copper, molybdenum zinc, nitrogen, phosphorus and potassium favoring its growth over other species. When water hyacinth dies, sinks and decomposes, the water becomes more eutrophic due to the large release of nutrients. Water quality can deteriorate, threaten clean drinking water and impact human health. At present, solutions for controlling the spread of water hyacinth are divided into three general categories: physical, chemical and biological control. Biological control has been promoted as the best means for controlling water hyacinth and currently is an important area of research. Biological control includes the utilization of natural enemies, pathogens and allelopaths; however, our knowledge and understanding of the biology and ecology of water hyacinth is limited. To effectively control water hyacinth through biological means, it will be necessary to study more thoroughly the physiology, population and community dynamics, and ecosystem ecology of this species as well as interspecific competition, predation and its evolution. In this paper, we review the costs and benefits associated with the different control methods. We suggest that water hyacinth populations can be reduced and controlled by using an integrated management approach that combines biological control with a watershed management strategy that minimizes pollution and promotes a long term sustainable approach for effective water management in a region.