Effects of Water Hyacinth on the freshwater ecosystem

Posted on 24 Aug 2021

Water hyacinth (Eichhornia crassipes) is considered to be the world’s worst aquatic weed species due to its invasive potential, the negative impact it has on aquatic ecosystems, and the high costs involved in controlling the species. In South Africa, the species has been classified as a category 1b invasive species in the new 2020 Alien and Invasive Species List as part of the National Environmental Management: Biodiversity Act, 2004 9 Act no. 10 of 2004.

 

Originating in the Amazon basin, the free-floating plant quickly spread into other tropical and sub-tropical regions of the world, and eventually arrived in South Africa in the early 1900s. Due to the nutrient rich conditions of South Africa’s waters, the invasive weed was able to spread rapidly throughout South Africa’s waterways.

 

Water hyacinth degrades aquatic ecosystems due to its ability to rapidly infest water bodies which then suppress the native aquatic biodiversity, the obstruction of river flows which may aggravate flooding and promotes siltation, interfere with water utilization for activities such as recreation or irrigation, and increased rates of evapotranspiration from the water storages. The plant also allows provides ideal breeding conditions habituates for malaria-carrying mosquitos’ larvae as well as disease vectors such as the bilharzia snail.

 

Due to these factors and the limited water sources in South Africa, the species has been declared as a category 1b weed in terms of the National Environmental Management: Biodiversity Act (2004): Alien and Invasive Species regulations, 2012 which necessitates or eradication wherever possible.

 

Since the 1970s, control programs have been established in South Africa in an attempt to control the spread of the weed. Herbicides have traditionally been used to control the species with some success with biological control agents being less effective as an herbicide. Research (van Wyk, 2002) however indicates that that the cost-effectiveness of herbicidal control agents are five times less effective than either biological control or integrated control measures as it requires resource intensive follow up measures and thereby indicating that biological control agents are currently the most cost-effective control a for a sustainable, long term control strategy for the species. Species such as the small plant hopper (Megamelus scutellaris) has already been recorded to be an effective biological control species in South Africa and is currently being used along with twelve (12) other species in a control program on the Hartbeespoort dam.

 

ENVASS is more than capable to conduct site visits, identification, listing confirmation and the overall control and management programmes to ensure compliance with the latest laws and regulations. Feel free to contact us on 012 460 9768 or at info@envass.co.za for quotes on any environmentally related services!

 

Van Wyk, E. and Van Wilgen, B.W., 2002. The cost of water hyacinth control in South Africa: a case study of three options. African Journal of Aquatic Science27(2), pp.141-149.