LAKE KIVU is one of the
African Great Lakes
African Great Lakes . It lies on the border
Democratic Republic of the Congo
Democratic Republic of the Congo and
Rwanda , and is in
Albertine Rift , the western branch of the
East African Rift
East African Rift .
Lake Kivu empties into the
Ruzizi River , which flows southwards into
Lake Tanganyika . People on the shore at
Gisenyi , Rwanda.
* 1 Geography
* 2 Chemistry
* 3 Biology and fisheries
* 4 See also
* 5 References
Lake Kivu is approximately 90 km (56 mi) long and 50 km (31 mi) at
its widest. Its irregular shape makes measuring its precise surface
area difficult; it has been estimated to cover a total surface area of
some 2,700 km2 (1,040 sq mi). The surface of the lake sits at a height
of 1,460 metres (4,790 ft) above sea level. The lake has a maximum
depth of 475 m (1,558 ft) and a mean depth of 220 m (722 ft), making
it the world's eighteenth deepest lake by maximum depth, and the ninth
deepest by mean depth.
Some 1,370 km2 or 58 percent of the lake's waters lie within DRC
The lake bed sits upon a rift valley that is slowly being pulled
apart, causing volcanic activity in the area.
The world's tenth-largest island on a lake ,
Idjwi , lies in Lake
Kivu, within the boundaries of
Virunga National Park . Settlements on
the lake's shore include
Kabare , Kalehe , Sake , and
Gisenyi , Kibuye , and
Cyangugu in Rwanda.
Lake Kivu is a fresh water lake and, along with Cameroonian Lake Nyos
Lake Monoun , is one of three that undergo limnic eruptions .
Around the lake, geologists found evidence of massive biological
extinctions about every thousand years, presumably caused by
outgassing events. The trigger for lake overturns is unknown in Lake
Kivu's case, but volcanic activity is suspected. The gaseous chemical
composition of exploding lakes is unique to each lake. In Lake Kivu's
case, methane and carbon dioxide due to lake water interaction with a
The amount of methane is estimated to be 65 cubic kilometres. If
burnt over one year, it would give an average power of about 100
gigawatts for the whole period. There is also an estimated 256 cubic
kilometers of carbon dioxide. The water temperature is 24 °C, and the
pH level is about 8.6. The methane is reported to be produced by
microbial reduction of the volcanic CO2. The risk from a possible
Lake Kivu overturn is catastrophic, dwarfing the historically
documented lake overturns at Lakes Nyos and Monoun, because
approximately two million people live in the lake basin.
Cores from the
Bukavu Bay area of the lake reveal that the bottom has
layered deposits of the rare mineral monohydrocalcite interlain with
diatoms , on top of sapropelic sediments with high pyrite content.
These are found at three different intervals. The sapropelic layers
are believed to be related to hydrothermal discharge and the diatoms
to a bloom which reduced the carbon dioxide levels low enough to
Scientists hypothesize that sufficient volcanic interaction with the
lake's bottom water that has high gas concentrations would heat water,
force the methane out of the water, spark a methane explosion, and
trigger a nearly simultaneous release of carbon dioxide. The carbon
dioxide would then suffocate large numbers of people in the lake basin
as the gases roll off the lake surface. It is also possible that the
lake could spawn lake tsunamis as gas explodes out of it.
The risk posed by
Lake Kivu began to be understood during the
analysis of more recent events at Lake Nyos. Lake Kivu's methane was
originally thought to be merely a cheap natural resource for export,
and for the generation of cheap power. Once the mechanisms that caused
lake overturns began to be understood, so did awareness of the risk
the lake posed to the local population.
An experimental vent pipe was installed at
Lake Nyos in 2001 to
remove gas from the deep water, but such a solution for the much
Lake Kivu would be considerably more expensive. No plan has
been initiated to reduce the risk posed by Lake Kivu. The
approximately 500 million tonnes of carbon dioxide in the lake is a
little under 2 percent of the amount released annually by human fossil
fuel burning. Therefore, the process of releasing it could potentially
have costs beyond building and operating the system.
This problem associated with the prevalence of methane is that of
mazuku , the Swahili term "evil wind" for the outgassing of methane
and carbon dioxide that kills people and animals, and can even kill
vegetation when in high enough concentration.
A methane extraction platform.
Lake Kivu has recently been found to contain approximately 55 billion
cubic metres (1.94 trillion cubic feet) of dissolved biogas at a depth
of 300 metres (1,000 ft). Until 2004, extraction of the gas was done
on a small scale, with the extracted gas being used to run boilers at
Bralirwa brewery in
Gisenyi . As far as large-scale exploitation
of this resource is concerned, the Rwandan government has negotiated
with a number of parties to produce methane from the lake.
In 2011 ContourGlobal, a U.S. based energy company focused on
emerging markets, secured project financing to initiate a large-scale
methane extraction project. The project will be run through a local
Rwandan entity called KivuWatt, using an offshore barge platform to
extract, separate, and clean the gasses obtained from the lake bed
before pumping purified methane via an underwater pipeline to on-shore
gas engines . Stage one of the project aims to build and supply three
"gensets" along the lake shore, totaling 25 MW of electrical capacity.
Initial project operations are scheduled to commence in 2012.
In addition to managing gas extraction, KivuWatt will also manage the
electrical generation plants and on-sell the electrical power to the
Rwandan government under the terms of a long-term Power Purchase
Agreement (PPA). This allows KivuWatt to control a vertically
integrated energy offering from point of extraction to point of sale
into the local grid. Extraction is said to be cost-effective and
relatively simple because once the gas-rich water is pumped up, the
dissolved gases (primarily carbon dioxide, hydrogen sulphide and
methane) begin to bubble out as the water pressure gets lower. This
project is expected to increase Rwanda's energy generation capability
by as much as 20 times, and will enable
Rwanda to sell electricity to
neighboring African countries. The firm was awarded the 2011 Africa
Power deal of the year for innovation in the financing arrangements it
obtained from various sources for the KivuWatt project. The $200
million power plant was operating at 26 MW in 2016.
BIOLOGY AND FISHERIES
Fishing boats on Lake Kivu, 2009. The sky reflected on
The fish fauna in
Lake Kivu is relatively poor with 28 described
species, including four introduced species . The natives are the Lake
Rukwa minnow (Raiamas moorii), four species of barb (
Ripon barbel ,
East African red-finned barb , Enteromius.
Redspot barb , Enteromius kerstenii and Pellegrin\'s
barb , Enteromius pellegrini), an
Amphilius catfish, two Clarias
catfish (C. liocephalus and C. gariepinus ),
Nile tilapia (Oreochromis
niloticus) and 15 endemic
Haplochromis cichlids. Another c. 20
possibly undescribed species of cichlids are known from the lake. The
introduced species are three cichlids, the longfin tilapia
(Oreochromis macrochir), O. leucostictus and redbreast tilapia
(Coptodon rendalli), and a clupeid, the
Lake Tanganyika sardine ,
The exploitable stock of the
Lake Tanganyika sardine was estimated at
2000–4000 tons per year. It was introduced to
Lake Kivu in the late
1959 by a Belgian Engineer A. Collart. At present,
Lake Kivu is the
sole natural lake in which L. miodon, a sardine originally restricted
to Lake Tanganyika, has been introduced initially to fill an empty
niche. Prior to the introduction, no planktivorous fish was present in
the pelagic waters of Lake Kivu. In the early 1990s, the number of
fishers on the lake was 6,563, of which 3,027 were associated with the
pelagic fishery and 3,536 with the traditional fishery. Widespread
armed conflict in the surrounding region from the mid-1990s resulted
in a decline in the fisheries harvest.
Following this introduction, the sardine has gained substantial
economic and nutritional importance for the lakeside human population
but from an ecosystem standpoint, the introduction of planktivorous
fish may result in important modifications of plankton community
structure. Recent observations showed the disappearance during the
last decades of a large grazer, Daphnia curvirostris , and the
dominance of mesozooplankton community by three species of cyclopoid
copepod: Thermocyclops consimilis , Mesocyclops aequatorialis and
Tropocyclops confinis .
The first comprehensive phytoplankton survey was released in 2006.
With an annual average chlorophyll a in the mixed layer of 2.2 mg
m−3 and low nutrient levels in the euphotic zone, the lake is
Diatoms are the dominant group in the lake,
particularly during the dry season episodes of deep mixing. During the
rainy season, the stratified water column, with high light and lower
nutrient availability, favour dominance of cyanobacteria with high
numbers of phototrophic picoplankton. The actual primary
production is 0.71 g C m−2 d−1 (≈ 260 g C m−2 a−1).
A study of evolutionary genetics showed that the cichlids from lakes
in northern Virunga (e.g., Edward , George , Victoria ) would have
evolved in a "proto-lake Kivu", much older than the intense volcanic
activity (20,000-25,000 years ago) which cut the connection. The
elevation of the mountains west of the lake (which is currently the
Kahuzi-Biega National Park , one of the largest reserves of eastern
lowland (or Grauer's) gorillas in the world), combined with the
elevation of the eastern rift (located in eastern Rwanda) would be
responsible for drainage of water from central
Rwanda in the actual
Lake Kivu. This concept of "proto-lake Kivu" was challenged by lack of
consistent geological evidence, although the cichlid's molecular
clock suggests the existence of a lake much older than the commonly
cited 15,000 years.
Lake Kivu is the home of four species of freshwater crab , including
two non-endemics (
Potamonautes lirrangensis and P. mutandensis ) and
two endemics (P. bourgaultae and P. idjwiensis ). Among Rift Valley
Lake Tanganyika is the only other with endemic freshwater
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