Alien Invasive Aquatic Plant Species in Botswana: Historical Perspective and Management

Abstract

Aquatic ecosystems in Botswana have been under threat by the aquatic alien invasive plant species viz., salvinia Salvinia molesta Mitchell, water lettuce Pistia stratiotes L., and water hyacinth Eichhornia crassipes (Mart.) Solms-Laub. While salvinia has been termed the major threat to the Botswana wetlands, water lettuce and water hyacinth are considered to be of minor importance. This review presents the species biology, distribution, historical spread, negative impacts, control achieved right from their discovery in the country by referring to their control and management in the world.Having infested the Kwando-Linyanti-Chobe Rivers in the 1970s, salvinia was initially tried by the use of herbicides, paraquat and glyphosate, between 1972 and 1976. With the discovery of the host specific biological control weevil Cyrtobagous salviniae Calder and Sands in 1981, the weevil was introduced by Namibians on Kwando and Chobe Rivers in 1983 and by Botswana in 1986 in the Okavango Delta. While the control was slowly establishing in Kwando-Linyanti-Chobe Rivers, it became apparent that lakes and perennial swamps within and outside Moremi Game Reserve of the Okavango Delta were infested with salvinia from 1992 onwards.With continuous and sustained liberation of the weevil in the Kwando-Linyanti-Chobe Rivers and in the Okavango Delta between 1999 and 2000, salvinia control was achieved by 2003, and since then the weevil constantly keeps the weed at low levels. The success is mainly due to sustainable monitoring through the application of physical and biological control methods. However, salvinia is still threatening the Okavango Delta due to factors such as tourism activities, boat navigation fishing and transporttion by wild animals.The first occurrence of water lettuce was recorded on Kwando and Chobe Rivers in 1986. Its biocontrol weevil Neohydronomous affinis Hustache was released in the year 1987. The weevil became extinct in Selinda Canal and Zibadianja Lake on Kwando River due to dry and wet events for over 10 years and the weed had been under control biologically on Chobe River. Having surface covered the Selinda and a part of the Zibadianja in high flood and rainfall in 1999/2000 season, research was undertaken to contain water lettuce, which led to its eradication by 2005. Regular physical removal of the water lettuce prior to fruit maturity is an effective method of control or eradicating the weed in seasonal water bodies.The Limpopo Basin (shared by Botswana, South Africa, Zimbabwe and Mozambique) has become vulnerable to water hyacinth infestation. Water hyacinth infested the trans-boundary Limpopo River in 2010 sourced from Hartbeesport Dam on Crocodile River in South Africa. Botswana and South Africa have been consulting each other to implement integrated control of the weed jointly in the Limpopo River. Water hyacinth could be a continuous threat to the dams and the rivers in the Limpopo basin if its control is not taken seriously.These three species are found growing in Botswana in a range of pH...

Are the Enrichment Nutrient Feasible to the Vermicomposting Efficiency For Water Hyacinth (E. Crassipes)?

“…Among the floating macrophytes that normally occur in eutrophic freshwater bodies, it stands the aquatic weed water hyacinth Eichhornia crassipes (Martius) Solms-Laubach (Pontederiaceae). This species is originally from South America with widespread invasive potential (Howard & Harley, 1997;Koutika & Rainey, 2015;Kurugundla et al, 2016;Cordeiro et al, 2020).…”

Spatial Dynamics of Invasive Para Grass on a Monsoonal Floodplain, Kakadu National Park, Northern Australia

“…Some authors estimate the greatest global loss of wetlands has been in Asia [2]. Exotic weed invasions are assessed to be one of the main drivers of ongoing degradation of wetlands, globally [1,3,4]. The current causes of wetland degradation and loss (human land uses, invasive species, water extraction and pollution) are expected to be exacerbated by concomitant impacts of climate change (i.e., changed temperature and rainfall regimes; risk of inundation from sea-level rise) [5].…”

Malezas acuáticas invasoras en aguas epicontinentales y una propuesta de aprovechamiento de Eichhornia crassipes (jacinto de agua) para la producción de biogás

“…El lago Tana es el tercer lago más grande de la cuenca del Nilo, con un área total de más de 67 mil ha (hectáreas), en dicho lago se ha reportado la presencia de E. crassipes, pues de acuerdo con Tewabe (2017), en 2011 la cobertura era de 80 a 100 ha y desde el año 2013 esta maleza aumentó su cobertura de 112 a 1512 ha en 2017 (Asmare et al, 2020). (Kurugundla et al, 2016).…”

“…En el delta del Okavango se descubrió por primera vez en 1986 a S. molesta, a partir de ahí se ha extendido en varios canales fluviales confinados a la Reserva de Caza Moremi (por sus siglas en inglés MGR) y a algunas áreas fuera de la Reserva.Una observación notable en 1996 fue la cobertura del 80% de la maleza en el lago Dombo, un importante lugar turístico en MGR (Kurugundla et al, 2016). Naidu et al (2000) reportaron la presencia de S. molesta, en esa misma reserva.…”

“…Naidu et al (2000) reportaron la presencia de S. molesta, en esa misma reserva. Se encontraron reportes en los años 2000, 2001, 2003 y 2015 de que esta misma especie se extendió a lo largo de los 60 km del río Khwai (Kurugundla et al, 2016).…”