Africa

The African continent has approximately 99 large wetlands, of which 43 are floodplain systems. Some of the larger floodplain systems include the Zaire Swamps (200 000 km2), the Inner Niger Delta of Mali (320 000 km2 when flooded), the Sudd of the Upper Nile (16 500 km2 of permanent swamp and 15 000 km2 of seasonal floodplain), and the Okavango (14 000 km2 of permanent swamp and 14 000 km of seasonal floodplain). These floodplain systems are in dynamic equilibrium with the constant flux of pulsing events occurring within them at different spatial and temporal scales. Goods and services resulting from pulsing events include floodplain recession agriculture, fish production, wildlife habitat, livestock grazing, eco-tourism, and biodiversity, as well as natural products and medicine.

In semiarid and arid regions of Africa, floodplains are often the only source of year-round water. As in other floodplains around the world, vegetation distribution is strongly related to flooding frequency and duration and microtopography. Dense evergreen tree growth occurs on higher well-drained areas like levees and termite mounds, while grasslands tend to dominate lower, more frequently flooded areas. Typical grasses found growing in these frequently flooded areas (called swamp) include Phragmites, Typha, and Polygonum. Tree and bush genera in less frequently flooded areas include Hyphanene, Borassus, Acacia, Ficus, and Kigelia.

Floodplain areas are centers of high diversity of animal and plant life. These floodplain areas are of profound importance for fish production and probably serve as spawning and recruitment areas. Interannual fluctuations in fish production have been correlated with the flooding regime. Numerous bird species (over 400 in some flood-plains) can be found in these areas, including bee-eaters, jacanas, malachite kingfishers, grey herons, egrets, African fish eagles, and Zaire peacocks. The birds share the flood-plains with antelope (sitatunga, waterbuck, puku, and lechwe), hippopotamus, zebra, and buffalo; vegetation ranges from water lilies and papyrus to floodplain forests with minor topographical variations playing an important role in distribution of forest and grassland. Climatic variations are also important, with forest only occurring near rivers in drier areas while in wetter areas forests can extend for a considerable distance away from the river.

River meanders tend to be cut off during flooding periods, adding diversity to the floodplain topography.

Unfortunately, very few studies of the ecology of many of the African floodplain systems have been carried out. The most studied floodplain system in Africa is the Okavango Delta. Annual floods travel uninterrupted down the Okavango River and inundate the Okavango Delta from April to September. River water is characterized by moderate levels of nutrients, but when it enters the floodplain it becomes strongly enriched by nutrients via leaching from soil, detritus, and feces. Organic carbon enrichment comes from leaching of floodplain leaf litter and soil, although dissolved organic carbon release from leaf litter is over 2 orders of magnitude greater than for leached soils. This nutrient enrichment has a major impact on aquatic productivity in the delta and illustrates the strong links between terrestrial and aquatic ecosystems.

African floodplains face a different set of challenges as opposed to those in developed countries. In Africa, flood-plains generally occur in semiarid areas to arid regions, and flooding is the driving force behind the high productivity of these areas. From as early as the 900s, people have inhabited these areas, and pastoral and agricultural economies are dependent upon the continued presence of the floodplains. Continued pressures from agricultural practices within the floodplains themselves and population growth that demands the transfer of water to alleviate shortages outside of the floodplain need to be addressed to ensure survival of these important ecosystems.

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