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# of Endemic Species
520: Lake Chad
Major Habitat Type:
xeric freshwaters and endorheic (closed) basins
Ashley Brown, WWF-US, Conservation Science Program, Washington, DC, USA
Christian Lévêque, Centre National de la Recherche Scientifique (CNRS), Paris, France and Emmanuel Obot, Nigerian Conservation Foundation, Lagos, Nigeria
Cameroon; Central African Republic; Chad; Niger; Nigeria; Sudan
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.
Drainages flowing into:
Main rivers or 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).
The climate of Lake Chad is semi-arid to arid (Olivry et al. 1996). Conditions are dry and hot from March to June and dry and cool from November to February. On the east coast of the lake, the minimum and maximum air temperatures are about 14o C and 31.4o C in January, 24.2o C and 38.5o C in April, and 24.2o C and 31o C in August (Olivry et al. 1996). Precipitation occurs from June to October, with the northward movement of an unstable, maritime air mass. Average rainfall over the lake is 212 mm per year in the north and 288 mm per year in the east.
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).
The Sahara Desert, which borders the northern-most section of the lake, has little to no vegetative cover (Wanzie 1990).
A rich fish fauna adapted to seasonal flooding and large bird congregations distinguish the Lake Chad ecoregion (Ezealor 2002). During the period of Normal Chad, fish species exhibiting a wide distribution in the lake and its tributaries have included Lates niloticus, Synodontis schall, Labeo senegalensis, Distichodus rostratus, Hydrocynus forskalii, and Schilbe mystus.
The lake’s aquatic biota, and particularly its fish fauna, are highly susceptible to changes in water levels and chemistry, as evidenced by the 1972-75 drought (Bénech et al. 1983; Dumont 1992). During those years, decaying vegetation caused deoxygenation of waters and local fish mortality. The north basin, isolated from the rest of the lake, suffered large moralities due to fishing pressure and degraded environmental conditions in the waters that remained in the lake basin (Bénech et al. 1983). Low flows in rivers constrained the seasonal fish migrations (Dumont 1992). Lacustrine species, often migratory and more selective in spawning preference, suffered from high mortality and fewer accessible spawning sites (Bénech 1992).Local extinctions occurred for several species such as Heterotis niloticus and Hydrocynus brevis. Natural selection operating on the fish communities during this dry period favored the development of "marshy" species adapted to survive in harsh environments. Fish that became more dominant included lungfish (Polypterus senegalus), Oreochromis niloticus, Oreochromis aureus, Sarotherodon galilaeus, Brienomyrus niger, and Clarias spp. (Bénech et al. 1983; Dumont 1992). Lungfish cope with anoxic conditions through aerial breathing, while Oreochromis and Sarotherodon are tolerant of low oxygen conditions.
Other noteworthy aquatic biotic elements:
Waterbirds flock to the productive waters of Lake Chad during the wet season. Lake Chad is located along a major route for migratory birds, serving as a resting stop for southbound migrants (Dejoux 1983). Wading birds frequent the mud flats and over one million wintering ducks congregate along the edges of Lake Chad (Dejoux 1983; Denny 1991). The Hadejia-Nguru wetlands host large populations of several overwintering ducks, including the white faced whistling-duck (Dendrocygna viduata) (maximum count 47, 879 in 1996) and fulvous whistling-duck (D. bicolor) (maximum count 4080 in 1992) (Scott & Rose 1996; Ezealor 2002). The ducks often congregate around mats of submerged vegetation in the floodplain (Dejoux 1983). In a July 1997 count, 41,386 individual waterbirds from 38 species were counted in the Hadejia-Nguru wetlands. This number increased to 65 species and 274,993 individuals with inclusion of overwintering migrants (Dodman et al. 1999). On the Logone floodplains large populations of Anas querquedula have been reported (maximum count 25,000) (Scott & Rose 1996).
In addition, there are twenty-five species of aquatic molluscs reported from the ecoregion and three endemic species (Gabbiella neothaumaeformis, G. tchadiensis, and Biomphalaria tchadiensis); however, Brown (1994)) suggests that further studies may reveal that these species are more widespread(Brown 1994). The ecoregion is also home to 36 water-dependent frog species, with only one species strictly endemic to the ecoregion (Astylosternus nganhanus).
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 , 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:
Bénech, V. (1992)"The northern Cameroon floodplain: Influence of hydrology on fish production" In Maltby, E.;Dugan, P.;LeFueve, J.C. (Ed.). Conservation and development: the sustainable use of wetland resources. (pp. 155-164) Gland, Switzerland: IUCN.
Bénech, V., Durand, J. R., et al. (1983)"Fish communities of Lake Chad and associated rivers and floodplains" In Carmouze, J.P.;Durand, J.R.;Leveque, C. (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.
Carmouze, J. P., Durand, J. R., et al. (1983)"The lacustrine ecosystem during the "Normal Chad" period and the drying phase" In Carmouze, J.P.;Durand, J.R.;Leveque, C. (Ed.). Lake Chad, Monographiae Biologicae 53. (pp. 527-560) The Hague: Dr W. Junk Publishers.
Carmouze, J. P., Durand, J. R., et al. (1983) Lake Chad: Ecology and productivity of a shallow tropical ecosystem. The Hague: W. Junk.
Carmouze, J. P.,Lemoalle, J. (1983)"The lacustrine environment" In Carmouze, J.P.;Durand, J.R.;Leveque, C. (Ed.). Lake Chad: Monographiae Biologicae 53. (pp. 27-63) The Hague: Dr W. Junk Publishers.
Compére, P.,Iltis, A. (1983)"The phytoplankton" In Carmouze, J.P.;Durand, J.R.;Leveque, C. (Ed.). Lake Chad, Monographiae Biologicae 53. (pp. 145-198) The Hague: Dr W. Junk Publishers.
Dejoux, C. (1983)"The fauna associated with the aquatic vegetation" In Carmouze, J.P.;Durand, J.R.;Leveque, C. (Ed.). Lake Chad, Monographiae Biologicae 53. (pp. 273-292) The Hague: Dr W. Junk Publishers.
Denny, P. (1991)"Africa" In Finlayson, M.;Moser, M. (Ed.). Wetlands. (pp. 115-148) London, UK: International Waterfowl and Wetlands Research Bureau.
Dodman, T., Béibro, H. Y., et al. (1999). "African waterbird census 1998" Dakar, Senegal: Wetlands International.
Dumont, H. J. (1992). "The regulation of plant and animal species and communities in African shallow lakes and wetlands" Revue Hydrobiological Tropical 25(4) 303-346.
Hammer, Theodore U. (1986). "Saline lake ecosystems of the world" Dordrecht, The Netherlands: Dr W. Junk.
Hollis, G. E., Adams, W. M., et al. (1993). "The Hadejia Nguru wetlands. Environment, economy and sustainable development of a Sahelian floodplain wetland" Gland, Switzerland: IUCN.
Iltis, A.,Lemoalle, J. (1983)"The aquatic vegetation of Lake Chad" In Carmouze, J.P.;Durand, J.R.;Leveque, C. (Ed.). Lake Chad, Monographiae Biologicae 53. (pp. 125-143) The Hague: Dr W. Junk Publishers.
Lévêque, C. (1997) Biodiversity dynamics and conservation: The freshwater fish of tropical Africa. Cambridge, UK: Cambridge University Press.
Lowe-McConnell, R. H. (1985)"The biology of the river systems with particular reference to the fishes" In Grove, A.T. (Ed.). The Niger and its neighbors. (pp. 101-140) The Netherlands: A. A. Balkema.
Nasa (2001) "A shadow of a lake: Africa's disappearing Lake Chad" <http://www.gsfc.nasa.gov/topstory/20010227lakechad.html>(2003)
Olivry, J. C., Chouret, A., et al. (1996) Hydrologie du lac Tchad, Monographie Hydrologique, 12. Paris: ORSTOM.
Scott, D. A.,Rose, P. M. (1996). "Atlas of Anatidae populations in Africa and Western Eurasia. Wetlands International Publication 41" Wageningen, T he Netherlands: Wetlands International.
Wanzie, C. S. (1990). "Water resources management and wildlife conservation in the Lake Chad Basin" Mammalia 54(4) 579-585.