Lake Tanganyika
| Lake Tanganyika | |
|---|---|
 | |
| Coordinates | |
| Lake type | Rift Valley Lake |
| Primary sources | Ruzizi River Malagarasi River Kalambo River |
| Primary outflows | Lukuga River |
| Catchment area | 231,000 km² |
| Basin countries | Burundi The DRC Tanzania Zambia |
| Max length | 673 km |
| Max width | 50km / 72km |
| Surface area | 32,900 km² |
| Average depth | 570m |
| Max depth | 1,470m |
| Water volume | 18,900 km³ |
| Shore length1 | 1,828 km |
| Surface elevation | 773m[1] |
| Settlements | Kigoma, Tanzania Kalemie, DRC |
| 1 Shore length is an imprecise measure which may not be standardized for this article. | |
Lake Tanganyika is a large lake in Central Africa that is estimated to be the second largest freshwater lake in the world by volume and the second deepest, in both cases after Lake Baikal in Siberia. It is also the world's longest freshwater lake and one of the world's oldest lakes, having been formed around twenty million years ago.
Located at the southern end of the Western Rift Valley, the lake is divided among four countries — Burundi, Democratic Republic of Congo (DRC), Tanzania, and Zambia. The water flows into the Congo River system and ultimately into the Atlantic Ocean. During the slave trading period, it was a major transshipment route for slavers. The old Arab slave-trading town of Ujiji, on the eastern shore of the lake, is where Henry Morton Stanley greeted David Livingstone with the words, "Dr. Livingstone, I presume?"
Geography
The lake is situated within the Western Rift of the Great Rift Valley that runs from Lebanon to Mozambique and is confined by the mountainous walls of the valley. It is the largest rift lake in Africa and the second largest lake by surface area on the continent. It is the deepest lake in Africa and holds the greatest volume of fresh water. It extends for 673 km in a general north-south direction and averages 50 km in width. Much of the lake's coastline is high escarpment, falling directly into the lake.
The lake covers 32,900 km², with a shoreline of 1,828km and a mean depth of 570 m and a maximum depth of 1,470 m (4,823 ft) (in the northern basin). It holds an estimated 18,900 km³ (4500 cubic miles). It has an average surface temperature of 25°C and a pH averaging 8.4. Additionally, beneath the 500 meters of water there is circa 4,500 meters of sediment overlaying the rock floor.
Of the four countries into which it is divided, the DRC (45 percent) and Tanzania (41 percent) possess the majority of the lake.
The enormous depth and tropical location of the lake prevent "turnover" of water masses, which means that much of the lower depths of the lake are so-called fossil water and are anoxic (lacking oxygen). The catchment area of the lake covers 231,000 km², with two main rivers flowing into the lake, numerous smaller rivers and streams (due to the steep mountains that keep drainage areas small), and one major outflow, the Lukuga River, which empties into the Congo River drainage.
The major inflows are the Ruzizi River, entering the north of the lake from Lake Kivu, and the Malagarasi River, which is Tanzania's second largest river, entering in the east side of Lake Tanganyika. The Malagarasi predates Lake Tanganyika and was formerly continuous with the Congo River.
Biology
Lake Tanganyika is home to more than 2,000 plant and animal species, and is one of the richest freshwater ecosystems in the world. About 600 of these species exist nowhere else in the world outside the Lake Tanganyika watershed.
The lake holds at least 250 species of cichlid fish and 150 non-cichlid species, most of which live along the shoreline down to a depth of approximately 600 feet. Lake Tanganyika is thus an important biological resource for the study of speciation in evolution.
The largest biomass of fish, however, is in the pelagic zone (open waters) and is dominated by six species — two species of "Tanganyika sardine" and four species of predatory Lates (related to, but not the same as, the Nile Perch that has devastated Lake Victoria cichlids).
Almost all (98 percent) of the cichlid species are endemic (exclusively native) to the lake and many, such as fish from the brightly colored Tropheus genus, are prized within the aquarium trade. This kind of elevated endemism also occurs among the numerous invertebrates in the lake, most especially the mollusks, (which possess similar forms to that of many marine mollusks), crabs, shrimps, copepods, jellyfishes, leeches, etc. Other animals found are the hippopotamus and the crocodile.
The Gombe Stream National Park and the Mahale Mountains National Park, both on the eastern shore, are famous for their chimpanzees.
Industry
It is estimated that 25–40 percent of the protein in the diet of the people living around the lake comes from lake fish, and that population amounts to around one million. Currently there are around 100,000 people directly involved in the fisheries operating from almost 800 sites. The lake is also vital to the estimated 10 million people living in the basin. Lake Tanganyika fish can be found throughout East Africa.
Commercial fishing began in the mid-1950s and has had an extremely heavy impact on the pelagic fish species; in 1995 the total catch was around 180,000 tons. Former industrial fisheries, which boomed in the 1980s, have subsequently collapsed. Poor farming practices in the surrounding hills coupled with aggressive deforestation has brought heavy amounts of sediment into Lake Tanganyika, smothering its vegetation, which is vital to the fish population. In addition, unregulated large-scale commercial fishing has further depleted the lake’s resources.
Sports fishing targets include some of the largest fresh water species such as the Nile Perch, Golden Perch, Goliath Tigerfish, Lake Tanganyika Yellow Belly (Ncupi), and large Vundu Catfish.
researchers have found multiple lines of evidence showing that increasing air and water temperatures and related factors are shrinking fish and algae populations in a major lake. The lake holds 18 percent of the world’s liquid freshwater and is a critical food source in East Africa.
Reporting in the August 14, 2003, issue of the journal Nature, Catherine O'Reilly of Vassar College, Andrew Cohen of the University of Arizona, Simone Alin of the University of Washington, Pierre-Denis Plisnier of the Royal Museum for Central Africa in Belgium, and Brent McKee of Tulane University in Louisiana, announce that climate change in the region is harming Lake Tanganyika's ecosystem, decreasing fish stocks by as much as 30 percent over the past 80 years.
Lake Tanganyika is large and deep, filling the chasm of a rift valley bordering the Democratic Republic of Congo, Tanzania, Zambia and Burundi. An ecosystem unto itself, the lake supports many types of fish. Only a few species are eaten by people, yet they supply 25 to 40 percent of the animal protein for the communities of that region. Recently, the fish supplies have diminished, and catches are shrinking.
"Our research provides the strongest link to date between long-term changes in lake warming in the tropics, recorded by instruments, and declining productivity of the lake's ecosystem, as seen in sediment cores," said Cohen. "This work provides a clear indication of the regional effects of global climate change, and especially global warming, on tropical lake ecosystems."
The researchers measured lake water temperatures, along with air temperatures and wind velocities, and compared data to equivalent records from the past eight decades. Those factors help determine how well water circulates within the lake, a critical factor for the distribution of nutrients that support life in the lake's food chain.
"This is an important study that demonstrates the dramatic response of a lake ecosystem to changes in climatic and environmental conditions over a relatively short period of time," said Jarvis Moyers, director of the Division of Atmospheric Sciences at the National Science Foundation (NSF), the independent federal agency that supports fundamental research and education across all fields of science and engineering and a sponsor of this research.
Ultimately, O'Reilly and her colleagues found that temperatures have increased 0.6 degrees Celsius in the air above the lake, with a proportional increase in the water temperature, while wind velocities have decreased.
Those temperature changes stabilize the water column in lakes, especially in the tropics where, unlike in temperate regions, winter cooling and mixing is absent. The increased stability decreased circulation, hampering the re-supply of nutrients from the deep water to the surface waters of the lake where they help algae grow. The algae, which form the base of Lake Tanganyika's food chain, ultimately feed the commercially important fish.
Future predictions for this region indicate a roughly 1.5 degree Celsius rise in air temperature, said O'Reilly—further stabilizing the lake and reducing mixing, with potentially devastating effects on fish stocks.
"Continued climate warming has some severe implications for the nutrition and economy of the region's people, who depend heavily on the lake as a natural resource," said O'Reilly. "To date, most studies have found significant effects of climate change in the northern hemisphere," she added, "while our study indicates that substantial warming is also occurring in the tropics, and that it is having a negative impact on some ecosystems."
In addition to finding evidence of warming in lake water temperatures and decreased windiness from instrument records, the researchers analyzed organic matter from well-dated lake sediment cores and found clues that life in the ecosystem has been on the decline.
Information from the sediments indicated that algae abundance declined 20 percent over the 80-year period for which data exists. The researchers believe the decline is a direct result of the reduction in lake circulation. Based on earlier studies of other lakes, that decline would lead to a 30 percent reduction in fish stocks, in addition to any possible effects of over-fishing.
"The fisheries of Lake Tanganyika currently yield approximately 200,000 tons of fish per year, and are far and away the most important source of animal protein for human consumption in this region of Central Africa," said Cohen. "Given the already significant problems of malnutrition and civil conflict in central Africa, a significant decline in fishing yields resulting from climate change could lead to extremely serious consequences for the region’s food supply," he added.
Transport
Two ferries carry passengers and cargo along the eastern shore of the lake - the MV Liemba between Kigoma and Mpulungu and the MV Mwongozo, which runs between Kigoma and Bujumbura.
- The port town of Kigoma is the railhead for the railway from Dar es Salaam in Tanzania.
- The port town of Kalemie is the railhead for the DRC rail network.
History
Formed during the upheavals that created the Great Rift Valley twenty million years ago, the African Great Lakes were affected by the ice age of eighteen thousand years ago. The increased aridity caused Lake Victoria to dry up completely, while the shorelines of Lake Tanganyika and Lake Malawi fell at leaat 400 meters below their present levels.
The Ha tribespeople who live at the northern end of the lake today have an oral tradition that they have always lived in the region they call Buha. Therefore, they may have been among the first Bantu groups to arrive from Central Africa, about two thousand years ago.
Slaves captured by Arab traders from as far west as the Congo River basin were transported in the nineteenth century across Lake Tanganyika to Ujiji. From there they were marched to the Indian Ocean, a 1,200-kilometer walk that took from three to six months. It has been estimated that during the fifty years that the Omani Arabs controlled the route, over a million East Africans were shipped to the coast this way.
The first known Europeans to find the lake were the explorers Richard Burton and John Speke, in 1858. They located it while searching for the source of the Nile River.
World War I
The Lake was the scene of two famous battles during World War I. The Germans had complete control of the lake in the early stages of the war. When the Allies cut off the railway link in July 1916, the Germans abandoned the area. To avoid his prize ship falling into Allied hands, they scuttled the vessel, which was later resurrected and renamed as the MV Liemba.
Recent history
An earthquake along the East African Great Rift Valley fault line struck on December 5, 2005, approximately 6 miles (10 km) below the surface of Lake Tanganyika. Its estimated magnitude was between 6.3 and 6.8 on the Richter scale.
Early reports indicated that the heaviest damage was sustained by the eastern provinces of the Democratic Republic of Congo, a region already ravaged by extensive war and extreme poverty. The area houses tens of thousands of refugees displaced by conflicts. Dozens of houses collapsed in the DRC city of Kalemie.
The quake was centered roughly below Lake Tanganyika and — in addition to the DRC, where the most widespread damage was reported — it was felt in Burundi, Tanzania, Rwanda, and as far away as the capital cities of Kenya and Angola.
The lake is hemmed in by mountains that run parallel with its shores. The mountains and the lake are all oriented northwest to southeast along the boundary of the Somalian and Nubian plates. The most dramatic elevation change is beneath the surface of the lake, where Lake Tanganyika plunges to a depth of 1,470 meters. If the geologic forces that created the lake continue, eastern Africa will eventually break away from the rest of Africa and the Great Rift Valley will become ocean.
ReferencesISBN links support NWE through referral fees
Sources and further reading
- Finke, Jens. 2003. The Rough Guide to Tanzania. 1st ed.
External links
- Food and Agriculture Organization of the United Nations
- [1] Food and Agriculture Organization of the United Nations
- [2] Action Against Hunger Retrieved October 2, 2007
- [3] Lake Tanganyika Biodiversity Project
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