Sudd wetlands

Category: Inland Aquatic Biomes.

Geographic Location: Africa.

Summary: This hydrologically dynamic ecosystem is a vital resource for many animal species as well as domesticated fauna; its location near arid, war-torn areas has disrupted conservation efforts.

The Sudd Wetlands biome of South Sudan, found in the lower reaches of Bahr-El-Jabal segment of the White Nile River, is the one of largest tropical wetlands in the world, and was designated as a Ramsar Wetland of International Importance in 2006. Sudd is derived from the Arabic word sadd, meaning “blockage of river channels, or obstruction to navigation.” The wetlands ranges 310 miles (500 kilometers) from south to north, and 124 miles (200 kilometers) east to west.

Hydrology and Climate

The average expanse of wetland or marshland here is 11,600–15,450 square miles (30,000–40,000 square kilometers), but this mushrooms to as vast an area as 50,000 square miles (130,000 square kilometers) during times of major flooding. The area contains thick grassland and vegetation over heavy clay soils that prevent absorption of surface water. Sandy earth is found 98 feet (30 meters) below ground, evidence that groundwater does not readily percolate to the surface of this biome. In general, Lake Victoria and its influence on the White Nile are the key sources of inundation here.

The mean annual temperature in the Sudd is 91 degrees F (33 degrees C) during the hot season, and 64 degrees F (18 degrees C) during the cold season. Annual rainfall ranges from 23 inches (600 millimeters) in the north to 39 inches (1,000 millimeters) in the extreme south of the wetland. The relative humidity is 23 percent during the dry season and a steamy 88 percent during the wet season. Because of hot, humid conditions, more than half of the inflowing water from the Nile system is lost through evapotranspiration across the permanent and seasonal floodplains. To avoid evaporation losses and increase the amount of water discharged at the outlet of the Sudd for agricultural and municipal uses, a planned 223-mile (360-kilometer) canal—the Jonglei Canal—is being constructed to bypass the swamps and carry some of the river’s waters directly to the main channel.

The nearby segment of the Nile River, called alternately the Upper White Nile or Albert Nile locally, is the extreme north outlet of Lake Albert. Its waters run north to the town of Nimule, South Sudan, where it is called Bahr-El-Jabal. The river’s meandering path here carves various channels and lagoons during the dry season and expands broadly over the partly flooded grasslands during the wet season.

Part of the wetlands fall within a sprawling system of mudflats in the arid Sahelian region of Africa. Essentially, the Sudd wetlands form as a function of the river channels exceeding their carrying capacity and periodically overflowing their banks. The Sudd wetlands are in a sense composed of interconnected river channels, associated with huge flood plains. Closer to the rivers are the permanent swamp areas. The more substantial part of the Sudd manifests as seasonal swamps, mainly created by Nile flooding but sometimes directly from heavy rainfall events when isolated ponds overflow.

Biodiversity

Ecologically, the Sudd Wetlands comprise various ecosystems: open water and submerged vegetation, floating fringe, seasonally inundated woodland, rain- and river-fed grasslands, and floodplain scrubland. The swamps and floodplains, in particular, support a rich biota with more than 400 bird and 100 mammal species. Migratory birds make favored stopovers here, while many wetland birds inhabit the extensive floodplains, including shoebills, great white pelicans, and black crowned cranes.

The wetlands are a haven for an estimated 1.2 million herd animals, including such migrating mammals as antelopes—among them the endangered Nile lechwe, reedbuck, tiang, and the world’s largest population of white-eared kob.

The Sudd also is a habitat for many species of freshwater mammals such as hippopotamus, and reptiles such as the crocodile, as well as amphibians. As a giant filter that controls and normalizes water quality and functions as an enormous sponge to stabilize regional water flow, the Sudd is the major source of water—and abundant grazing plants—for domestic livestock as well, especially Nilotic cattle.

The deep open water areas of the biome are mainly surrounded by a permanent swamp zone consisting of Cyperus papyrus, Vossia cuspidata, and Typha spp., which are important habitats for shoebill stork. This zone, in turn, tends to be surrounded by seasonally flooded grasslands consisting of Echinochloa stagnina, E. pyramidalis, and Oryza longistaminata, as well as Hyparrhenia ruffa at the edge of the wetland. The Cyperus papyrus, which is threatened elsewhere by pollution and flood control, flourishes in the pristine Sudd wetlands.

Human Interaction

The Sudd is the home of Suddia, a plant genus known only to exist in this region, and which is thus endemic. Trees, shrubs, and both perennial and annual grasses provide various ecological services in the area, and also play a vital subsistence role for nomadic herdsmen, small farmers, and urban dwellers.

The wetlands provide substantial socioecological values for the region’s Dinka, Nuer and Shilluk tribal communities. The Dinka and Nuer tribes depend on the annual floods and rain to regenerate floodplain grasses that feed their cattle herds; the indigenous communities also use the wetlands and scrublands for firewood, mud, and other construction material. Through this intimate relationship with the biome, these indigenous peoples have come to take pride in ownership and have developed custodial vigor in efforts to preserve the area’s balanced but dynamic natural resources.

Climate change has already arrived in the Sudd. The regular seasonal patterns have been somewhat disrupted, with the dry periods lasting longer than they did formerly, and the rainy seasons more often producing heavier, damaging flood events. The seasonal changes affect crop growth, holding back some farm types while expanding the grazing areas, and may contribute to extinction of plant species; these factors could easily combine to make the area more vulnerable to the less-predictable weather.

The local growth and in-migration of the human population is meanwhile putting new strain on the water supply system. This is presenting tough challenges in a region already wracked by a civil war that lasted from 1983 to 2005. These socio-economic developments, particularly the civil conflict, have hampered protection and conservation efforts well into the twenty-first century. However, South Sudan had made enough progress in its conservation measures that it submitted the Sudd Wetlands as a candidate for the United Nations Educational, Scientific and Cultural Organization (UNESCO) World Heritage List in 2017.

Bibliography

Dumont, H. J., ed. The Nile: Origin, Environments, Limnology and Human Use (Monographiae Biological). Dordrecht, Netherlands: Springer Science & Business Media B.V., 2009.

Postel, S. The World Watch Environment Alert Series. New York: Norton, 1992.

“Sudd Wetland.” United Nations Educational, Scientific and Cultural Organization, 2022, whc.unesco.org/en/tentativelists/6276/. Accessed 31 Aug. 2022.

Stanton, E. A. “The Great Marshes of the White Nile.” Journal of the Royal African Society 2 (1903).

Wetlands International. Waterbird Population Estimates. 3rd ed. Wageningen, Netherlands: Wetlands International, 2002.