Swamps of the Upper White Nile

The Sudd swamps developed from a large lake which extended north to Khartoum during the Pleistocene. The main channels are stable over decades, but the bends show upstream migrations of about 20 m in 3 years. In permanent swamps the channels often have a band of Vossia, backed by papyrus, which in turn is backed by an extensive area of Typha domingensis. Before 1950 the Nile Cabbage, Pistia stratiotes, was an important part of the floating vegetation in permanent swamps, but in recent years it has been largely replaced by Eichhornia crassipes.

Seasonal flooding enables the growth of grasses such as Echinochloa spp. and Oryza longistaminata. Further from the channels, where rain is the main source of water, Hyparrhenia rufa is the main grass. The grasslands grade into open woodland with Acacia seyal and Balanites aegyptiacus.

A rich fauna was associated with Pistia, and a similarly rich fauna has developed around the invasive Eichhornia. The marginal vegetation shelters an association of microcrustacea, with a biomass 100 times that in the open water. Macroinvertebrates are also abundant and diverse; for instance there are at least 70 species of aquatic Coleoptera, 60 species of mosquitoes, and a special fauna of terrestrial forms occurs in the umbels of papyrus. About 68 species of fish occur, and they occupy a wide range of niches, from mud feeders to carnivores.

Mammalian swamp dwellers include Hippopotamus, and several antelopes such as the Sitatunga and Nile Lechwe, while the White-eared Kob makes large migrations in the seasonal grasslands.