Lake Chad



ID

520

Author(s)

Ashley Brown, WWF-US, Conservation Science Program, Washington, DC, USA


Countries

Cameroon
Central African Republic
Chad
Niger
Nigeria
Sudan

Reviewer(s)

Christian Lévêque, Centre National de la Recherche Scientifique (CNRS), Paris, France and Emmanuel Obot, Nigerian Conservation Foundation, Lagos, Nigeria


Major Habitat Type

Xeric freshwaters and endorheic (closed) basins

Drainages flowing into

Endorheic basin


Main rivers to other water bodies

Lake Chad falls within Niger, Chad, Cameroon, and Nigeria. The lake swells with seasonal river floods, and supports a rich fish fauna and large waterbird congregations within an otherwise xeric region. Due to Chad\'s flat lakebed, small changes in the water budget cause large variations in its area within and between years. For example, in 1965 the lake occupied 25,000 km2, while in 1973 it was reduced to 6,000 km2 (Carmouze et al. 1983b). By 2001 the lake was further reduced to less than 2,500 km2, due to the combined effects of increased water extraction upstream and climate desiccation (NASA 2001).

The lake’s water comes primarily from precipitation on the Adama Plateau in the south via the Logone River and from the northern highlands of the Central African Republic via the Chari River. These two rivers comprise 95% of the total lake inflow, with the Chari contributing 50% of the lake’s total water input in October and November (Carmouze & Lemoalle 1983; Evans 1996; Olivry et al. 1996). The Yobe in the northwest and the seasonally inundated riverbed El Beid contribute the remaining inflow. Flooding of the Logone and Chari occurs from September to December, while the El Beid floods from November to January. During high floods, water may pass from the Logone floodplains to the Niger River through the Mayo Kebbi System in the south of Chad.

The water chemistry of the lake is tied closely to climatic conditions. The Harmattan winds and dry season aridity contribute to high evaporation that often equals or exceeds water influx and can reach rates of up to 2,300 mm/year (Carmouze et al. 1983b; Hammer 1986). Wind also contributes to mixing of the shallow, polymictic lake, so that waters are always turbid: measurements of transparency have fluctuated from a mean of 1 m in 1965 when the water level was high, to 0.1 m in 1973 at the time of Sahelian drought (Carmouze & Lemoalle 1983). In spite of the lake’s endorheic nature and arid environment, water remains fresh as a result of hydrochemical regulation mechanisms. The salinity of the water, however, increases from the Chari delta to the north of the lake. The influx of fresh water from the south pushes the denser saline water to the north, where it leaves by seepage into a subterranean system (Dejoux 1983).



Description

Boundaries

Located at the southern edge of the Sahara desert, the Chad basin is bounded in the north by the Aïr and Tibesti Mountains, in the east by the Ennedi and Jebel Marra, and in the west by the Jos Plateau. This ecoregion encompasses the Lake Chad basin – a system with a large, floodplain lake in a xeric region on the edge of the Sahara.

Freshwater habitats

There are extensive floodplains on the Logone and Chari Rivers. These include the ‘Yaéré floodplain in Cameroon, composed of over 5,000 km2 of inundated land located between the Chari and Logone in the east and the Mandara Mountains in the west (Carmouze & Lemoalle 1983). Estimates of the total inundated area south of Lake Chad during the rainy season are as high as 90,000 km2 (Lowe-McConnell 1985). On the north-west side, the Hadejia-Nguru floodplain (6,000 km2), an important wetland for resident waterbirds and Palearctic migrants, drains to the Yobe River (Hollis et al. 1993; Ezealor 2002).

During a “Normal Chad” period, the lake landscape is a mixture of open water (38%), archipelagoes (23%) and reed belts (39%) (Dumont 1992). Separating the lake into north and south basins is the Grand Barrier, a ridge of land submerged when the lake is fully inundated. The south basin, with more inflow, is usually the larger basin. These basins and the southeastern archipelago zone, an area studded with sandy islands, comprise the three main sections of the lake (Carmouze & Lemoalle 1983).

Vegetation of the south basin is mainly composed of Cyperus papyrus, Phragmites mauritianus, Vossia cuspidata, and other associated wetland macrophytes. The more saline northern basin supports Phragmites australis and Typha australis. The shoreline is lined with the reed Cyperus laevigatus in the north and Cyperus articulatus, Pycreus mundtii and Leersia hexandra in the south (Iltis & Lemoalle 1983). Hyphaene thebaïca (doum palm) marks the base of the slope of the dunes, which are colonized by Balanites aegyptiaca, Leptadenia pyrotechnica, Calotropis procera, and Acacia spp. Submerged vegetation (such as Ceratophyllum demersum, Potamogeton schweinfurthii, and Vallisneria spiralis) grows in the lake. Over 1,000 species of algae have also been described from the lake (Compére & Iltis 1983).

Terrestrial habitats

The Sahara Desert, which borders the northern-most section of the lake, has little to no vegetative cover (Wanzie 1990). 

Ecological phenomena

As the influent Chari and Logone Rivers swell as a result of seasonal rains, fish migrate from the lake up the rivers and onto productive floodplains for feeding and breeding. Flooding brings high phytoplankton and zooplankton productivity to the floodplains, as well as increased macrophytic growth, creating ideal feeding and spawning habitat (Carmouze et al. 1983a). For example, macrophytic vegetation of floodplains, such as the Yaéré floodplains, provides shelter, breeding, or feeding habitat for juveniles of many different species (Bénech et al. 1983; Dumont 1992). Migratory species that move to floodplains to spawn include Alestes baremose, A. dentex, Distichodus rostratus, Brachysynodontis batensoda, and Marcusenius cyprinoides

Justification for delineation

As with the Inner Niger Delta [508], the Lake Chad ecoregion is distinguished based on the ecological role it plays for migrating wetland birds. The ecoregion is also characterized by a relatively widespread, Sudanian freshwater fauna and is included within the Nilo-Sudan bioregion. During the Pleistocene, Lake Chad was likely connected to the Niger, Nile, and probably Congo River basins. At present, the Chad basin occasionally connects with the Niger basin during flooding of the Mayo Kebbi system in southern Chad (Olivry et al. 1996). However, the Gauthiot Falls between the Benue River (within the Niger basin) and the Mayo-Kebi (Chad basin) has prevented the dispersal of some Niger basin aquatic species into the Lake Chad basin. Fish species such as Citharidium ansorgii, Arius gigas, Synodontis ocellifer, and Cromeria nilotica, among others, inhabit the Benue River, but do not occur in the Chad basin (Lévêque 1997). The recent isolation of the lake basin and the large fluctuations in water level explain the absence of aquatic endemics in such a historically large lake (Dumont 1992; Lévêque 1997).

Level of taxonomic exploration

Good


References

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  • Bénech, V., Durand, J. R. and Quensière, J. (1983). "Fish communities of Lake Chad and associated rivers and floodplains" J. P. Carmouze, J. R. Durand and C. Leveque (Ed.) Lake Chad, Monographiae Biologicae 53 ( pp. 293-356 ) The Hague: Dr W. Junk Publishers.
  • Brown, David (1994). "Freshwater snails of Africa and their medical importance" London, UK: Taylor & Francis.
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  • Carmouze, J. P., Durand, J. R. and Lévêque, C. (1983). "The lacustrine ecosystem during the "Normal Chad" period and the drying phase" J. P. Carmouze, J. R. Durand and C. Leveque (Ed.) Lake Chad, Monographiae Biologicae 53 ( pp. 527-560 ) The Hague: Dr W. Junk Publishers.
  • Carmouze, J. P. and Lemoalle, J. (1983). "The lacustrine environment" J. P. Carmouze, J. R. Durand and C. Leveque (Ed.) Lake Chad: Monographiae Biologicae 53 ( pp. 27-63 ) The Hague: Dr W. Junk Publishers.
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  • Dejoux, C. (1983). "The fauna associated with the aquatic vegetation" J. P. Carmouze, J. R. Durand and C. Leveque (Ed.) Lake Chad, Monographiae Biologicae 53 ( pp. 273-292 ) The Hague: Dr W. Junk Publishers.
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