Lake Chad
Flat, changed annually shorelines
Lake Chad is an endorheic lake in West, Central Africa. It lies on the southern edge of the Sahara in the Chad Basin, and is divided among the States Chad, Cameroon, Nigeria and Niger. Two Dreiländerecke are located in the Lake: Cameroon - Chad - Nigeria in the southeastern part and Niger Chad Nigeria in the northwestern part. Both are no longer covered by the open water surface of the lake, the water remaining area is divided into Chad and Cameroon.
In the public view of the lake came in the last decades by a dramatic drop in the water level ( adjacent satellite imagery), but this is based on a rather one-sided conservative point of view of a lake. Lake Chad has variable shorelines and water volume since time immemorial. As early as 1450, for example, dried out the southern basin of the lake, which was based on a shift of its main inflow and led to a flood disaster in the following years. In colonial times the region reported colonial officials that they have to do it year by year with changing shorelines of the lake. In a year they were able to cross areas of the sea floor on dry ground, in the following year they had for the selbige route using a boat. The fact is that the volume of Lake Chad is subject to long-term changes. His current volume is indicated generally at 73 km ³, but this only partially correlated with the changes in its water balance.
General
Lake Chad is one of the world's largest endorhëischen fresh water body, which is a unique and globally important ecosystem can by its marginal position to the desert Erg Kanem arise. He is referred to by its historically verifiable different water levels in the last one thousand years as the great, normal and small Chad. From the large Lake Chad is when the free water surface covered over 24,000 km ², level over 284.2 meters above sea level. Normal Lake Chad covered an area 18000-22000 km ², level 279-282 meters above sea level. From the small Lake Chad is when the free water surface between 2000 bis 14,000 km ² varies, levels below 278.5 meters. Under the mark of 2,000 km ², the then remaining Chad to the characteristics of a very large wetland.
The lake basin of Lake Chad normal is divided into a northern and a southern basin, which are separated by the Altdünenzone the Great Barrier or Grande barrier, thus have taken place hydrochemical exchanges only when water levels over 280 meters. The fourth geographical sector of the normal Lake Chad is called Archipelago, it lies to the northeast of the eastern bulge of the lake. The northern basin has a depth of seven meters, the southern a depth of three to four meters. In the eastern part of the southern lake basin, the valley of Wadi Bahr -el- Ghazal joins, this forms an overflow channel of the lake, towards the deepest valley in the Chad Basin, the Bodélé depression. This is flooded from a level of 13 meters above lake bottom, most recently in 1962 and 1964.
The since the 1970s observed regression of the lake peaked in the late 1990 's. The no longer constantly covered by the open water surface of the lake areas nowadays form of a large wetland that is designated by the WWF, the Lake Chad flooded savanna. This area stands out as the Lake Chad Wetlands protected under the Ramsar Convention, whose largest dimension are in Nigeria, where they are referred to as Lake Chad Game Reserve since 2008. It is the first protected transboundary wetland of international importance on the African continent.
History
The history of Lake Chad is closely linked to the climatic conditions of the region, but also reflects the climate history of the whole earth resist. Thus, the expansion of the lake to almost 2 million square kilometers about 50,000 years ago were found. It extended from the Tibesti and Ennedi mountains to the Central African emerging from. The lake dried up in the age of Ogolien or Kanemien until about 22,000 years ago completely out of which was to last until about 12,000 years ago. Then the humid phase of the first Nigéro - Tschadien dawned, in which the lake has a depth of 15 meters reached before he dried again 11,000 years ago. In Nigéro - Tschadien II, 9000 years ago, the lake was able to recover and reached a depth of 38 meters before he fell to one of the current magnitude comparable size. The biggest expansion during the era of Nigéro - Tschadien reached the sea 6000-4000 years ago today, he reached a water depth of approximately 65 meters and an area of approximately 350,000 km ². After that, its water surface reduced to 60,000 km ² in 2000 years ago, with 36.000 km ² 1,000 years ago. The smallest size yet assignable size reached Lake Chad in 1908, when he dried up to a few wetlands in northern and southern basin. He then actively embarrassed to a size 22900-25000 km ² in 1963. Early 1970s began a series of droughts in which the lake continues to shrink, down to a maximum of 4000 km ² in 2001. In 2008 he had a minimal extension of 30 x 40 km at the mouth of the Shari, which corresponded to an open water area of 2,500 km ².
Hydrology
The water catchment area of Lake Chad has an area of about 967,000 km ² and is referred to by the Lake Chad Basin Commission as a conventional basin. About 90 percent of its water received by the lake from the tributaries of the Chari (French Chari ) and in N'Djamena opening into the Chari Logone. Less than ten percent of the feed come from Nigerian rivers and the local rainfall. Primarily, it involves the Komadugu Yobe and the El Beid. Of lesser importance are the Ngadda and Yedseram, however, reach most Nigerian rivers, except the El Beid, since the great droughts of the 1960s - 80s no longer the open water of the small Lake Chad. All these rivers carry water all year round, but are subject to seasonal fluctuations in level. The regional rainfall occurs in the months of June to September. They are controlled by the intensity of the West African monsoon system. There are only between 250 and 450 mm of rainfall per year in the region of Lake Chad. The lake is generally described as a typical representative of fresh water lakes in the Sahel, these are characterized by their very low salinity.
Thus, the water balance of Lake Chad is very much dependent on rainfall in common, about 800 km distant catchment area of Chari and Logone. The Rhythm of the rainy seasons varies the water level of the lake and flooded miles of flat land or withdraws accordingly. In the small depth ( in large areas of the lake it is less than one meter, at the lowest points hardly more than five) and the high evaporation rate ( generally one goes annually by 2300 mm ) to its banks shift constantly. Due to increasing population, there was also amplified to water use and withdrawal from the lake and its tributaries (drinking water, agriculture). When reduced, the goods transported by Shari water quantities by more than 50 percent during the 1960s, its surface had decreased dramatically. The regression took through the droughts of the 1970s to even dramatic proportions. The northern lake basin dried up completely; in the south remained low water surface. Nigeria lost its share of the open water surface completely. New settlements on trockengefallenem lakeside emerged in all the countries mentioned above, since the released land is very fertile and can thus be used well for agriculture. In some cases they had to be abandoned in part, after the shorelines of shallow water areas shifted in opposite directions by an increase in precipitation. Whether this will continue in the future since 1998 observed transgression, is uncertain. There are considerations to supply water from the opening into the Congo Ubangi via a channel to the Chari and thus Lake Chad. These plans are seen by environmental groups critical ( displacement of native plant and animal species).
Swaying With average rainfall to several decimetres, the lake level is currently at about 240 m above sea level. Sea level and covers approximately 23,000 km ². A comparable with the Caspian Sea expansion - such as the extent of 300,000 square kilometers - had the lake around 4000 BC The water level was then about 50 m higher. For this ancient lake basins, the term Mega - Chad was introduced by geoscientists.
Ecology
To understand the ecology of the current Lake Chad, it is appropriate to look at the lake with its highly variable coastlines. Its water level varies not only seasonally, but also between years. The period of low water is in the months of May / June. With the arrival of the summer monsoon rainfall, the lake begins to expand. The flood season in its tributaries reach the lake in October / November, so that the lake in December / January reached its maximum water mark to then shrink again. The lake flooded a large area of several thousand square kilometers a year. 1998, however, was the minimal size of the lake about 1750 km ², its maximum extent approximately 6000 km ². 2001 fluctuated between 4,000 km ² water surface, with 19.000 km ². The water coverage in the northern basin mainly depends on the inflow of Komadugou Yobe and Ngadda; This has an approximate volume of 0.5 to 0.8 km ³ per year. In water-rich years can be up to 6000 square kilometers, the water coverage in low-water years, however, it is dry. In this hydrodynamic and ecological point of view, the term lake near Lake Chad in part is also misleading, more appropriate to consider the Lake Chad as a wetland, on the one hand, the water depth of the free water surface is only one to three meters on average. On the other hand, large parts of the normal Lake Chad with islands and sedge islands are covered. This Archipelago called area makes up about 62 % of the total area of the normal Lake Chad, which the free water surface is only 38%. (: Lake Chad wetlands dt ) denotes For this reason, the Lake Chad is the WWF ecoregion as the Lake Chad Flooded Savanna. The extension of this ecoregion is approximately 19,000 km ² and includes the geographically separated Hadejia - Nguru wetlands with a. Another special feature of the lake is quite a long four-to five-month flood season in its tributaries. This long flood season results from the four - to six-month monsoon season in the headwaters and the vast wetlands of the Chari / Logone / El Both- flow system. These wetlands in the Massenya level, level of Bahr Aouk / Salamat, Logoneebene / Toupouri Valley and the Grand Yaeres together have an area of about 80 to 90,000 km ². Take on much of the monsoon rainfall in the upper reaches of the rivers, but give it off slowly. The ecology of wetlands contributes to the richness of algae of Lake Chad. Due to the flooding and drying of the levels created ideal conditions for the growth of algae, zoo - and phytoplankton, together over 1000 species have been detected in the lake of the food and form the basis for the diverse fish fauna.
Flora and Fauna
The information on the fish fauna are different in the highest degree. To occur in the Lake Chad fish species include the African osteoglossid ( Heterotis niloticus ), carp fish Labeo coubie that Salmlerarten Citharinus citharus and Citharinus distichodoides and various Alestes species, catfish of the genera Clarias, Schilbe and Synodontis, the Nile perch (Lates niloticus ), cichlids of the Tilapia relationship, including Oreochromis niloticus and the pufferfish Tetraodon fahaka. Endemic is the Salmlerunterart Brycinus nurse dageti.
From the avifauna of about 372 species of birds have been identified. The region of Lake Chad has been designated by BirdLife International as an Important Bird Area (IBA ). The wetlands of the lake have a special significance for migratory birds from the northern hemisphere, which use the wetlands as a resting and wintering quarters. Thus, in the seasonal wetlands before under other Ruff ( Philo pugnax ), the Witwenpfeifgans ( dendrocygna viduata ), the Garganey (Anas querquedula ) and Pintail ( Anas acuta).
The lake and its wetlands includes the Nile come ( Crocodylus niloticus ), hippopotamus (Hippopotamus amphibius) and on the banks of animals such as antelopes, elephants and monkeys.
The flora in the vegetation zone of the southern lake basin is determined by the large areas with the genuine papyrus ( Cyperus papyrus ), Phragmites the mauritianus, Vossia cuspidata and other marsh plants are covered. On the open water of the lake the water lettuce floating ( Pistia stratiotes ) and this covers a large area of the lake. In the area of the northern lake basin the reed (Phragmites australis) and Typha australis dominate the vegetation. The plants like papyrus also have a significant economic importance. This is from the Buduma ( Yedina ) used to build their reed boats. Thor Heyerdahl used the knowledge of three Buduma Reed boat builder to build the Ra I which should 1969 5.000 km above the Atlantic Ocean sailing year.
Seasonal arises in the southern shore of the lake region the Yaérés vegetation. This is dominated by the grasses Echinochloa pyramidalis, Vetiveria nigritana, Oryza longistaminata and Hyparrhenia rufa. The Yaéré vegetation dies in the dry season. The humid zones of Yaérés be referred to as the Karal or Firki levels. The tree stands in these planes are mostly by seyal (Acacia seyal ) and the Fragrant acacia ( Acacia nilotica ) is formed. The vegetation in this savannah is formed by up to 2 to 3 meters tall herbs and grasses, such as the Caperonia palustris, Echinochloa colona, Hibiscus asper, Hygrophila auriculata and Schoenfeldia gracilis.
Research history to Lake Chad
Near its shore archaeologists found the oldest pottery in West Africa and in Konduga in Northeast Nigeria a dugout, whose age is dated to eight thousand years. The lake surrounding landscape at that time with a more humid and cooler climate than today, a crisscrossed by numerous tributaries Savannah, the people living there provided ample food resources and was settled very early. Several long-term regression phase and weaker transgressions can be read at the former beach ridges that have been mapped by geomorphological investigations and after analysis of satellite photos. Beyond the wide beach ridge system, the Bama and Ngelewa Beach Ridges created sprawling lagoon landscapes with clay dark Vertisolen. From 1800 BC, people increasingly penetrated into the former lagoon areas where settlements were established on the flood- free sandy islands in the Lehmebene. At the local level the southwest of the lake altitude area of Firki levels the Gajiganna culture marks the beginning of the Holocene colonization by the early and mittelholozänen high water levels of Lake Chad. The most famous archeological site of this early culture of West Africa is Zilum, this had been in the late phase of Gajiganna culture proto- urban trains on how moats and ramparts. Other archaeological sites of this culture are Kursakata, Mege and Ngala. The archaeological evidence of Gajiganna culture are mostly simple clay figures of people and animals, as well as pottery with simple decorations, such as prints by Matt braids. After the fourth century BC, no evidence of this culture more known. With this culture, the transition from a society of hunter -gatherers to food producers in the savanna West / Central Africa could be documented.
The settlement of the Lake Chad continues, about 2000 years ago, dip the first archaeological evidence of people who produced iron objects and used, south of Lake Chad on. The Iron Age cancels this time in this region of Lake Chad. A well-known archeological site of this period is Mdaga. In this period also marked the beginning of the Trans-Saharan trade is suspected in the region of Lake Chad is said to have played an important terminus on the route between Tripoli, the Fezzan and the Kaouar Valley. Notes on such trade can be found in Herodotus and Claudius Ptolemy, the latter reported on a country Agisymba in the 2nd century, which to this day is controversial, where this country really was. The next archaeological assignable culture in the region of Lake Chad can be found from the sixth century AD, with the appearance of Sao culture. Occupation is the Sao culture until the 17th century. Typical of this culture is the production of large urns and small terracotta figures.
According to the generally accepted historical research wandered in the 7th century nomadic Zaghawa in today's region of Kanem, northeast of Lake Chad area, a. They are considered the founder of the kingdom of Kanem, the mythical founding father Sef (Arabic: Saif ) was, however, the exact circumstances of the Empire are largely in the dark. According to the Immigration theory of the Bayreuth Dierk Lange, refugees from the defunct in the 6th century BC Assyrian Empire should have reached around 600 BC, the region of Lake Chad and have taken significant influence on the cultures of the region. According to this theory, the Assyrians are said to have the actual founding fathers of the empire, however, this theory is highly speculative, since no archaeological, cultural and historical evidence has been provided. Evidence can be early Islamization of the region around the lake in 10-11. Century, through the power of the Sayfawa dynasty in the kingdom of Kanem.
First written accounts of the region of Lake Chad can be found in al - Yaqubi in his end of the 9th century published Kitaab al - Buldaan ( Geography of the World or book the country ), in which he reports from the land Kanim, but without mention of the Lake Chad. About the Lake Chad can be found only in the 11th century, Abū ʿ Ubayd information on Al- Bakri. Therefore, one can only since this time geographically clearly between Kanem, east, and Bornu, west of Lake Chad, differ. He also tells of great mosques, as well as havens and are on individual ethnic groups information. However, it is believed that the Niger and Lake Chad are part of the Nile River system. Another source is Ibn Said, in Granada / Spain -born Muslim cartographer. He reports from Kuuri Lake, which is part of the stream of the Nile from Ghana to Egypt. He also reports that Kanimis navigated over the lake and the southern Seeanwohner, the Sao, would not disdain human flesh, while the inhabitants of Kanimis were good Muslims. Other Arab sources are Al - Dimashqi (1256-1327) from Damascus and Abu `l - Fida ( 1273-1331 ), also from Damascus, is known.
The first European mention of Lake Chad can be found in Leo Africanus, who traveled in the region in 1513 and reported Shary and Lake Gaoga in his work Descrittione dell'Africa of a country. Other sources can be found in the Encyclopedia L' Universale Fabrica, written by Giovanni Lorenzo Anania, this describes the Rio Negro, the Niger, and the Lago di Sauo, Lake Chad. This work was published in 1571-1592 in several volumes and served until the 19th century many cartographers as the source literature for the description of the region.
As sub-Saharan Africa represented a kind of terra incognita until the 19th century for the European cultural area, these are the only sources of the region of Lake Chad from the Middle Ages to the Renaissance. The first modern reports submitted by the German Friedrich Conrad Hornemann, who traveled in the region in 1800 in the British mandate; other reports submitted by Denham, Clapperton and Oudney from the year 1822. Probably the most famous travel reports where the Lake Chad was mentioned, derived from Heinrich Barth, Adolf Overweg and Gustav Nachtigal.