Location and General Description
The White Nile (known in various sections as the Bahr-el-Abiad, Bahr-el-Jebel, Albert Nile, and Victoria Nile) rises in the headwaters of Lake Victoria in a region of year-round rainfall, and after running through Uganda, overflows in southern Sudan into a shallow depression within the Kalahari Sands, creating the Sudd swamps at 380-450 m above sea level. The gradient of the river through the Sudd is greater than that on its subsequent course from Malakal to Khartoum (Beadle 1981). The southern portion of the floodplain is wetter than the northern, receiving on average about 800 mm/yr compared to the north’s 600 mm/yr. These rains fall between April and September (Moss 1998), and temperatures average 30-33oC during the hot season, dropping to an average of 18oC in the cold season. The Sudd swamps are extensive -- about 600 km long, and a similar distance wide. Vertisols are the main soils that have developed in the waterlogged conditions over these nutrient poor sediments, although fluvisols and patches of luvisols can be found along the river courses.
Since 1961, inflow to the Sudd has increased substantially, presumably due to increased rainfall in the headwaters around Lake Victoria. The inflow was 26,831 billion m3/year of water prior to 1960, but from 1960-1980, it averaged 50,324 billion m3/year (Hughes and Hughes 1992). The wetland area consequently increased dramatically until 1980, but the trends in recent years are not known.
The floodplain ecosystem supports a variety of plant species with a succession from those adapted to mesic environments to those adapted to xeric environs. Moving from the interior of the swamps, the ecological zones grade from the open-water and submerged vegetation of a river-lake, to floating fringe vegetation, to seasonally flooded grassland, to rain-fed wetlands and, finally, to floodplain woodlands (Hickley and Bailey 1987). Cyperus papyrus is dominant at riversides and in the wettest swamps. Phragmites and Typha swamps are extensive behind the papyrus stands and there is an abundance of submerged macrophytes in the open waterbodies. Seasonal flood plains, up to 25 km wide, exist on both sides of the main swamps. Wild rice (Oryza longistaminata) and Echinochloa pyramidalis grasslands dominate the seasonally inundated floodplains. Beyond the floodplain, Hyparrhenia rufa grasslands cover the rain-fed wetlands. Acacia seyal and Balanites aegypticaca woodlands border the floodplain ecosystem (Denny 1991).
The swamps and floodplains of the Sudd support a rich biota, including over four hundred bird species and one hundred mammal species. Migratory birds stopover and wetland birds inhabit the extensive floodplains of the Sudd, while large populations of mammals follow the changing water levels and vegetation.
During the 1980s, southern Sudan had among the highest population levels of antelope in Africa. Consequently, the IUCN/SSC Antelope Specialist Group (1999) has listed the Sudd as a key location for the recovery of threatened antelope in sub-Saharan Africa. Among the most abundant species found here are the white-eared kob (Kobus kob), the tiang (Damaliscus lunatus tiang) and the Mongalla gazelle (Gazella thomsonii albontata). These three antelopes make large-scale migrations over the relatively undisturbed habitat of the Sudd. For example, a million individuals of white-eared kob undertake a massive migration of over 1500 km, following the availability of floodplain grasses (Denny 1991). Over 800,000 individuals were estimated to inhabit Boma National Park in 1982/83 with population densities up to 1,000/km2 near food sources during the dry season (Fryxell and Sinclair 1988). The endemic Nile lechwe (Kobus megaceros) also occurs in this ecoregion, numbering about 30-40,000 individuals (Estes 1991). Listed as Threatened by the IUCN, it is subject to hunting and constrained by competition from cattle (Kingdon 1997). At present, its numbers are stable, although the Jonglei canal, irrigation or exploitation of oil in the region could change this (Kingdon 1997).
The floodplains provide important habitat for several species of birds. They support the largest population of shoebill (Balaeniceps rex) in Africa with an estimated population of roughly 5,000 (Stuart et al. 1990). The endangered white pelican (Pelecanus onocrotalus) flies over 2,000 km from Eastern Europe and Asia to reach one of its most important wintering grounds on the floodplains of the Sudd. The area is also a stronghold for the black crowned crane (Balearica pavonina), a species that has been designated Vulnerable by the IUCN (Newton et al. 1996; Shmueli et al. 2000).
Annual floods, capable of inundating more than 15,000 km2 of land, are crucial to the maintenance of biological diversity in the Sudd. Rainfall fills the swamps one to two months before the rivers overspill on to the floodplain. Welcomme (1979) estimated that only 11% of the total flooded area was permanent water, although this proportion may have increased in recent years. The floodwaters regenerate the floodplain with nutrients and allow the growth of forage plants. Occasional fires may also be an important disturbance here, but little research has been carried out regarding their importance to healthy ecosystem functioning.
The effective habitat block of the Sudd swamp is at least 30,000 km2 and the peripheral effects of the swamp are believed to extend over the entire 154,325- km2 ecoregion. Much of the Sudd swamps remain as a vast near-wilderness area, although it appears that the war has left management of protected areas seriously compromised, with poaching of large mammals proceeding unchecked (Stuart et al. 1990). The situation is exacerbated by the incomplete, empty Jonglei canal, which is acting as a game trap. This canal may have significant effects on some populations of large mammals.
According to Hughes and Hughes (1992), there are three designated game reserves in the Sudd. These are Zeraf Island (6,750 km2), Shambe (1,000 km2) and Mongalla (75 km2). Boma and Badingilo national parks also encompass portions of the Sudd. A recent assessment considered the level of protection and management in Boma and Badingilo National Parks as "nil" (East and IUCN/SSC Antelope Specialist Group 1999). It has also been proposed that a large extension of Shambe Game Reserve would ensure the protection of the ecoregion’s biodiversity (Stuart et al. 1990).
The Dinka, Nuer, and Shiluk tribes coexist in the Sudd with tens of thousands of large herbivores. These people depend on the annual floods and rain to regenerate floodplain grasses which feed their herds of cattle (Denny 1991). Fishing in the Sudd is also a means of livelihood. The human population density is under 20 persons/km2, and is concentrated along major rivers, lakes, and floodplains. The swamps are inhospitable.
Types and Severity of Threats
The civil war in southern Sudan poses the largest threat to conservation here. Lack of effective management and protection in the parks means that poaching is uncontrolled, and it is believed that populations of elephant (Loxodonta africana) have been decimated by poaching. Furthermore, it appears as if many large carnivores have been extirpated over much of the country, but lack of data makes it difficult to ascertain their status in the Sudd (Ginsberg, 2001).
Plans have existed for many years to divert the waters of the White Nile around the Sudd swamps via the Jonglei canal. Work on the canal began in 1978 but was stopped in 1984 for technical, financial and political reasons (Hughes and Hughes 1992). Diversion would prevent much of the evaporative loss of water that occurs in the Sudd, and it would allow this water to be used for irrigation, or other purposes downstream. Diversion would also cause the Sudd swamps and associated floodplains to shrink dramatically, possibly threatening the fauna and flora that depend on them for their survival. Even if the high levels of Nile discharge continue and the building of the canal proceeds, the swamps would still be larger than they were in the early 1960’s (Stuart et al. 1990). The Jonglei canal is likely to have a significant impact on climate, groundwater recharges, silt and water quality; it is also likely to involve the loss of fish habitat and grazing areas, which, in turn, will have serious implications for the local people. Future climate change as a result of global warming will also threaten the Sudd through altered rainfall patterns and water regimes. Increased variability in the hydrological cycle could cause inland wetlands to dry out and hence reduce their species diversity (UNEP 2001).
Justification of Ecoregion Delineation
This extent of this ecoregion, which is dominated by the Sudd wetland complex, was delineated based on expert opinion. It is a simplification of White’s complex vegetation mosaic for the area that includes ‘edaphic grassland mosaics with semi-aquatic vegetation’ and ‘edaphic grassland in the Upper Nile basin’. The intention was to define a maximum extent for the Sudd, primarily based on faunal distribution patterns (J. Kingdon).
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Prepared by: Colleen Seymour
Reviewed by: In progress