Duckweed, a growing concern...in two Eastern Cape Rivers

Phillippa C. Muskett, Jackie M. Hill, Phillip S.R Weyl - Department of Zoology and Entomology, Rhodes University, Grahamstown

Lemna spp, Spirodela spp and Wolffia spp (referred to as Duckweed) are considered native ubiquitous plants in South Africa that are becoming a growing concern in slow moving water bodies due to their extremely rapid growth.

Duckweed populations often dominate water bodies, in some cases with 100% cover, resulting in trickle down effects in the ecosystem.
These are very similar problems to those commonly associated with other invasive plants such as Water hyacinth (Eichhornia crassipes), Kariba weed (Salvinia molesta) and Water lettuce.

Several physiochemical as well as a bio control aspects of the Bushmans and the Bloukrans river systems in the Eastern Cape were studied.

These included macro invertebrate diversity, abundance and functional feeding groups as well as basic water parameters and nutrient analysis to gain an understanding of whether the populations are bottom-up or top-down driven.

Management of this nuisance plant may then require a reduction in available nutrients in problematic areas.

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