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Ecoregion Description


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Species Richness


# of Endemic Species


Threats

523: Lower Nile

Major Habitat Type:

xeric freshwaters and endorheic (closed) basins

Author:

Emily Peck, Conservation Science Program, WWF-US, Washington, DC, USA

Reviewers:

Robert Collins, University of California, Santa Barbara, USA and M. S. Farid, Water Resources Research Institute, Cairo, Egypt

Countries:

Egypt; Egypt, Administered by Sudan; Eritrea; Ethiopia; Sudan

Boundaries:

The lower Nile River provides a vital oasis for terrestrial and aquatic wildlife as it runs through the semi-arid Sahel and arid Saharan Desert of northern Sudan and Egypt. The boundaries of this ecoregion are defined by the lower Nile River from Khartoum, where the White and Blue Nile rivers converge, downstream to the Nile Delta [524]. Notable features of the ecoregion include four major cataracts over which the Nile flows before emptying into the Aswan High Dam’s massive reservoir, named Lake Nubia in Sudan and Lake Nasser in Egypt.

Drainages flowing into:

Mediterranean Sea

Main rivers or other water bodies:

 Primary water bodies in the ecoregion include the lower Nile River from Khartoum, where the White and Blue Nile rivers converge, downstream to the Nile Delta [524]; the areas draining to the lower Nile from the west; and areas draining from the east, including the Blue Nile and Atbara Rivers up to but excluding their uppermost reaches. Both the Blue Nile and the Atbara originate in the Ethiopian Highlands [525] and carry large amounts of sediments, estimated annually at 1.4 billion metric tons (Waterbury 2002).

Climate:

The arid desert climate in the central portion of the ecoregion becomes increasingly hostile toward the north. Two seasons occur in the ecoregion. A hot, dry summer exists from April though October, and a cooler winter exists from November through March. Northern Sudan experiences a high mean daily temperature of 35ºC in summer and 20ºC in winter, and receives a mere 20 mm of annual rainfall (Hughes & Hughes 1992). At Aswan in Egypt, temperatures range from a mean monthly minimum of 8ºC and maximum of 23ºC during the coolest month (January), to a minimum of 25ºC and maximum of 41ºC in the hottest month (August). Little to no precipitation falls in the Egyptian deserts. The western desert in Egypt experiences periods of years without rainfall, and precipitation in the hills of the eastern desert is highly variable. Streams can flow violently for several days after a storm drops up to 100 mm of precipitation, and then remain dry for several subsequent years (Hughes & Hughes 1992).

Freshwater habitats:

In the late spring, rain clouds from the South Atlantic reach the Ethiopian highlands and drop their precipitation, providing the annual Nile flood that reaches Egypt between mid-May and early July. Thereafter, the Nile surges with increasing volume for an average of 110 days, reaching its maximum height and volume in September. At the beginning of the flood in June, a parcel of water in the lower Nile will take twelve days to flow the six hundred miles from the Aswan High Dam to Cairo, but the same journey requires only six days in full flood in September. By November, the flood returns to its lower discharge levels (Collins 2002).

The total mean average annual flow of the Nile is 88 billion cubic meters (bilm³) of which the waters from Ethiopia (Blue Nile, Sobat, and Atbara) contribute 76 bilm³ or 86% of the total Nile discharge (Kendie 2001; Collins 2002). The Blue Nile flood is so large that it effectively blocks the flow of the White Nile at Khartoum, contributing an average 59%, or 52 billion m³, to the Nile’s total flow. Further north, the discharge from the Atbara contributes another 13% or 11 bilm³ (Collins 2002). Below the Atbara, the Nile flows through the harsh Nubian and Egyptian deserts for 2,415 kilometers without receiving any more water before discharging into the Mediterranean Sea. 

Lake Nubia/Nasser sits downstream of the Nile’s great “S” bend that is located between the Atbara confluence and the third cataract. When the reservoir behind the Aswan High Dam (Sadd al-Aali) is full, it covers an area of 6,850 km² and holds 140 billion m³ of water. The reservoir can be divided into three sections. The southern portion is situated in Sudan and is mainly riverine in nature; the middle section extends from Sudan north to Tushka in Egypt and has riverine characteristics only during seasonal floods; and the northern section, which lies entirely in Egypt, and is fully lacustrine (Hughes & Hughes 1992).

The Aswan High Dam has significantly altered the Nile\'s hydrologic regime (Beadle 1981). Previously, annual floods laden with nutria

nt-rich sediments sustained swamps between Khartoum and lower Egypt, and papyrus extended to the Nile Delta (Dumont 1986). The dam has caused the floodplains to virtually disappear (Welcomme 1979). When not in flood, the shallow (7-8 m average depth) lower Nile today has little energy and meanders through the wide, older channel, creating many in-channel islands (Abdelbary 1996; El-Sherbini et al. 1996).

A flat, featureless plain covers a majority of the ecoregion, though in the southeast the landscape rises sharply into the Ethiopian highlands through which flows the Great Abbai (Blue Nile) from Lake Tana. Fed by powerful tributaries, the Abbai runs through a deep canyon before entering onto the plains of the Sudan. The Blue Nile gorge has its own unique habitat with a narrow fringe of forest and scrub lining the river in its upper reaches (Rzóska 1978). From Khartoum downstream, the Nile valley is a broad flat plain over 300 km wide at its narrowest point and almost devoid of vegetation throughout the desert of northern Sudan. However, drought-tolerant plant species, such as Polygonum spp. and Potamogeton spp., occur in local stands and create narrow fringes along the mainstem Nile. Stands of Phragmites proliferate where the Nile flows into Lake Nubia (Dumont 1986; Hughes & Hughes 1992).

Below Lake Nasser, the Nile flows across a desert plateau, dividing it into two regions: the western desert, Sahara el Gharqiya, and the eastern desert, Sahara el Sharqiya (Hughes & Hughes 1992). The western desert is an arid sea of blown sand, becoming rocky towards the mainstem Nile. The eastern desert is bound by a discontinuous range of mountains that separates the Nile valley from the Red Sea. These mountains are extensively dissected by wadis (dry riverbeds that sometimes flow during flood events). The valley of the Nile River below Aswan Dam varies between 20-30 km in width and is confined by steep sides (Collins 2002).

At the northern edge of the ecoregion, west of the Nile mainstem, Lake Qârûn lies at the bottom of the Fayum depression, which is 71 km long and 20 km wide. Once fed by the Nile, Lake Qârûn now receives most of its flow as runoff from surrounding irrigated lands. As a result, its waters are becoming increasingly saline (Collins 2002).

Fish Fauna:

The lower Nile River provides vital habitat within a desert environment for an array of fish and other wildlife. Over 70 species of fish live in the ecoregion, many belonging to the families Alestiidae, Cichlidae, Citharinidae, Claroteidae, Cyprinidae, Mochokidae, and Mormyridae. 

Description of endemic fishes:

No fish are endemic to the lower Nile ecoregion. 

Other noteworthy aquatic biotic elements:

In the northeastern corner of the ecoregion, Lake Qârûn supports large number of waterbirds; several grebes, as well as Aythya fuligula, Fulica atra, and Anas crecca, are abundant. In the winter of 1989/90, over 32,000 birds congregated at the lake (Baha El Din 2001). Three species of turtle live within the lower Nile.

Of the nearly 50 indigenous taxa of molluscs within the entire Nile basin, 9 species are endemic. Within the Lower Nile ecoregion, 15 gastropods and 9 bivalves occur. Palearctic and Afrotropical species of gastropods overlap in the Saharan portion of the Nile basin, as well as in parts of the headwaters of the Blue Nile. For example, Brown (1994) (Brown 1994)observed Armiger crista living together with Ceratophallus natalensis and Segmentorbis angustus in a pool alongside a tributary to the Blue Nile River.

Justification for delineation:

The headwaters of the Blue Nile and Atbara Rivers are also separated into the Ethiopian Highlands ecoregion [525] due to their swift-flowing, steep nature and different aquatic fauna. The valley of the Nile River was inundated by the Tethys Sea up through the Cretaceous period (approximately 65 million years ago) (Dumont 1986). Five geologic phases of the Egyptian Nile can be distinguished, each separated by a dry period of no flow: the Eonile, Palaeonile, Protonile, Prenile, and the present Neonile (Rzóska 1978; Dumont 1986). The present Nile valley developed at the end of the Miocene. The rise of the high volcanic plateaus in Ethiopia, probably during the Oligocene, is responsible for the origin and direction of the Blue Nile and the Atbara River (Rzóska 1978). Tectonic movement and climatic changes have changed the Nile’s course and flow many times. The Nile Basin has few endemic fish, due to the frequent cessation of flow that inhibited the evolution and persistence of aquatic species (Beadle 1981; Dumont 1986).

Level of taxonomic exploration:

Good

References/sources:

Abdelbary, M. R. (1996)"Effects of the Aswan High Dam on Nile water and bed levels" In Shady, A.M.;El-Moattassem, M.;Abdel-Hafiz, E.A.;Biswas, A.K. (Ed.). Management and development of major rivers. (pp. 444-463) Calcutta, India: Oxford University Press.

Baha El Din, S. M. (2001)"Egypt" In Fishpool, L.D.C.;Evans, M.I. (Ed.). Important bird areas in Africa and associated islands: Priority sites for conservation. (pp. 241-264) Newbury and Cambridge, UK: Pisces Publications and Birdlife International.

Beadle, L. C. (1981). "The inland waters of tropical Africa" England: Longman Group Limited.

Brown, David (1994). "Freshwater snails of Africa and their medical importance" London, UK: Taylor & Francis.

Collins, R. (2002). "The Nile" New Haven, CT, USA: Yale University Press.

Dumont, H. J. (1986)"The Nile River system" In Davies, B.R.;Walker, K.F. (Ed.). The ecology of river systems. (pp. 61-74) Dordrecht, The Netherlands: Dr W. Junk Publishers.

El-Sherbini, A., El-Moattassem, M., et al. (1996)"Water quality condition of the Nile River" In Shady, A.M.;El-Moattassem, M.;Abdel-Hafiz, E.A.;Biswas, A.K. (Ed.). Management and development of major rivers. (pp. 162-175) Calcutta, India: Oxford University Press.

Hughes, R. H.,Hughes, J. S. (1992). "A directory of African wetlands" Gland, Switzerland, Nairobi, Kenya, and Cambridge, UK: IUCN, UNEP, and WCMC.

Kendie, D. (2001). "Egypt and the hydro-politics of the Blue Nile River" Northeast African Studies 6(1) 141-169.

Rzóska, J. (1974). "The upper Nile swamps, a tropical wetland study" Freshwater Biology 4 1-30.

Rzóska, J. (1978). "On the nature of rivers with case stories of Nile, Zaire and Amazon" The Hague, The Netherlands: Dr W Junk.

Waterbury, John (2002). "The Nile Basin: National determinants of collective action" New Haven, CT, USA: Yale University Press.

Welcomme, Robin L. (1979)"Fisheries ecology of floodplain rivers" In London, U. K. and New York, NY: Longman.

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