Tonlé Sap (; , ; or commonly translated as
'Great Lake
') is a
lake
A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...
in the northwest of
Cambodia
Cambodia, officially the Kingdom of Cambodia, is a country in Southeast Asia on the Mainland Southeast Asia, Indochinese Peninsula. It is bordered by Thailand to the northwest, Laos to the north, and Vietnam to the east, and has a coastline ...
. Belonging to the
Mekong River
The Mekong or Mekong River ( , ) is a transboundary river in East Asia and Southeast Asia. It is the world's List of rivers by length, twelfth-longest river and List of longest rivers of Asia, the third-longest in Asia with an estimated l ...
system, Tonlé Sap is the largest freshwater lake in
Southeast Asia
Southeast Asia is the geographical United Nations geoscheme for Asia#South-eastern Asia, southeastern region of Asia, consisting of the regions that are situated south of China, east of the Indian subcontinent, and northwest of the Mainland Au ...
and one of the most diverse and productive ecosystems in the world. It was designated as a
Biosphere Reserve
A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, funga, or features of geologic ...
by
UNESCO
The United Nations Educational, Scientific and Cultural Organization (UNESCO ) is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) with the aim of promoting world peace and International secur ...
in 1997 due to its high
biodiversity
Biodiversity is the variability of life, life on Earth. It can be measured on various levels. There is for example genetic variability, species diversity, ecosystem diversity and Phylogenetics, phylogenetic diversity. Diversity is not distribut ...
. During the 21st century, the lake and its surrounding ecosystems have come under increasing pressure from
deforestation
Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or urban use. Ab ...
, infrastructure development and
climate change
Present-day climate change includes both global warming—the ongoing increase in Global surface temperature, global average temperature—and its wider effects on Earth's climate system. Climate variability and change, Climate change in ...
.
Geography
Tonlé Sap Lake is located in the northwest of the lower Mekong plain, formed by the collision and collapse of the
Indian Plate
The Indian plate (or India plate) is or was a minor tectonic plate straddling the equator in the Eastern Hemisphere. Originally a part of the ancient continent of Gondwana, the Indian plate broke away from the other fragments of Gondwana an ...
and the
Eurasian Plate. The lower Mekong plain used to be a bay, and the sea level rose rapidly at the end of the last
glacial period
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
. About high, cores from this period found near Angkor contain tidal deposits, as well as salt marshes and
mangrove swamp
Mangrove forests, also called mangrove swamps, mangrove thickets or mangals, are productive wetlands that occur in coastal intertidal zones. Mangrove forests grow mainly at tropical and subtropical latitudes because mangrove trees cannot withs ...
deposits,
deposited in caves about 7,900-7,300 years ago The sediments of Lake Sap also show signs of marine influence. The current river morphology of the Mekong Delta was developed over the past 6,000 years,
while the remaining waters in the northwest corner of the lower Mekong plain formed the Tonlé Sap.
Hydrology
The Tonlé Sap
drainage basin
A drainage basin is an area of land in which all flowing surface water converges to a single point, such as a river mouth, or flows into another body of water, such as a lake or ocean. A basin is separated from adjacent basins by a perimeter, ...
is bordered to the southwest by the
Cardamom Mountains
The Cardamom Mountains (, ; , ), or the Krâvanh Mountains, is a mountain range in the southwest part of Cambodia and Eastern Thailand. The majority of the range is within Cambodia.
The silhouette of the Cardamom Mountains appears in the Sea ...
, with heights of more than , and to the north are the Piandan Mountains with an average height of . The basin covers an area of . The -long Tonlé Sap River connects the Tonlé Sap Lake with the Mekong River and contributes 9% of the flow of the Mekong River.
[ The size and water volume of the lake varies greatly throughout the year, with a minimum area of about and a volume of about in the dry season,][ and the water body expands in the rainy season, increasing the depth to . The maximum area is , and the volume is about .][
About 34% of the water in the Tonlé Sap comes from the rivers that enter the lake, about 53.5% from the Mekong River, and 12.5% from precipitation.][ May to October is the rainy season in the lower Mekong plain, and November to March is the dry season. The annual rainfall is . Almost all the precipitation is in the rainy season.] At the end of the dry season, the Tonlé Sap Lake has a typical depth of . As the monsoon rain begins, the water level
Water level, also known as gauge height or stage, is the elevation of the free surface of a sea, stream, lake or reservoir relative to a specified vertical datum.
Over long distances, neglecting external forcings (such as wind), water level ten ...
of the river begins to rise, eventually reversing the flow of the river. The water level of the Tonlé Sap increases by about , the flow of the Mekong gradually decreases at the end of the rainy season, and the flow of the Tonlé Sap then reverses and begins to replenish the flow of the Mekong.
The extreme hydrodynamic complexity of the Tonlé Sap Lake, both in time and space, makes it impossible to measure specific flow, and water level rather than velocity and volume determines the movement of water as it shapes the landscape. 72% of the modern sediments deposited in the Tonlé Sap come from the Mekong River, while only 28% come from the catchments upstream of the lake.[ Sediment-bound phosphorus acts as the basis of the food chain through phytoplankton, and internal nutrient cycling plays a crucial role in the productivity of the ]floodplain
A floodplain or flood plain or bottomlands is an area of land adjacent to a river. Floodplains stretch from the banks of a river channel to the base of the enclosing valley, and experience flooding during periods of high Discharge (hydrolog ...
and, therefore, the long-term sustainability of the lake's entire ecosystem.
Ecology
The land cover of the Tonlé Sap Lake Basin is 55% of the forest land and 45% of the agricultural land.[ The lake is surrounded by freshwater mangroves known as "flood forests",][ accounting for 3% of the basin area,][ and the floodplain is surrounded by low hills and covered with evergreen or deciduous seasonal tropical plants. The forest is dominated by ]Dipterocarpaceae
Dipterocarpaceae is a family (biology), family of flowering plants with 22 genera and about 695 known species of mainly lowland tropical forest trees. Their distribution is pantropical, from northern South America to Africa, the Seychelles, India ...
, Leguminosae
Fabaceae () or Leguminosae,[International Code of Nomen ...](_blank)
, Lacelandaceae, and in some places Pinaceae, Rohan pineaceae or bamboo. As the distance from the lake becomes farther and farther away, the forest gradually turns into a thicket, and finally into a meadow.[ In areas with higher quality soils or higher altitudes, deciduous mixed forests and semi-evergreen forests occur.][ This diversity of vegetation types underlies the species diversity of the Tonle Sap ecosystem, with interlocking forests, grasslands and swamps providing refuge for local wildlife.]
The lake is home to at least 149 species of fish, 11 of which are globally endangered, and the lake area is also home to 6 near-threatened species, including spotted-billed, great bald, bengal, black-bellied, and Grey-headed fish eagle and Far Eastern reed, in addition to supporting reptile populations including the endangered Siamese crocodile
The Siamese crocodile (''Crocodylus siamensis'') is a medium-sized freshwater crocodile native to Indonesia (Borneo and possibly Java), Brunei, East Malaysia, Laos, Cambodia, Myanmar, Thailand and Vietnam. The species is critically endangered and ...
and numerous freshwater snakes, and although much of the Lake District has been turned into farmland, 200 species of higher plants are still recorded. The Mekong giant catfish, which lives in the Tonlé Sap Lake, is one of the largest freshwater fish in the world. A fisherman caught a Mekong giant catfish weighing nearly 648 pounds in May 2004, but its population has been declining since the mid-1970s. It is currently illegal for fishermen to catch and retain Mekong giant catfish, and only a few are used for scientific research.
As a natural flood reservoir for the entire Mekong River system, Tonlé Sap Lake regulates floods in the lower reaches of Phnom Penh during the rainy season, and is also an important supplement to the dry season flow of the Mekong Delta
The Mekong Delta ( or simply ), also known as the Western Region () or South-western region (), is the list of regions of Vietnam, region in southwestern Vietnam where the Mekong, Mekong River River delta, approaches and empties into the sea th ...
. In 1997, UNESCO
The United Nations Educational, Scientific and Cultural Organization (UNESCO ) is a List of specialized agencies of the United Nations, specialized agency of the United Nations (UN) with the aim of promoting world peace and International secur ...
designated the Tonle Sap as a biosphere reserve, but scientists have been concerned that high dams built in southern China and Laos will affect the strength and flow of countercurrents into the Tonlé Sap, reducing the number of fish in the lake. Tonle Sap habitat for nesting, breeding, spawning, and foraging in the floodplain, which will adversely affect fish productivity and overall biodiversity in the Tonle Sap.
Forest loss
Deforestation or forest clearance is the removal and destruction of a forest or stand of trees from land that is then land conversion, converted to non-forest use. Deforestation can involve conversion of forest land to farms, ranches, or u ...
hotspots are located in low floodplain areas where protected areas are located, significant farmland expansion is mainly in the intersection between the lower and upper floodplains, population growth, fuelwood gathering and logging are the main causes of forest loss, intensification of agricultural activities and upstream hydropower development reduces buffers to natural habitats and increases the risk of forest loss. By the 2030s, hydropower development may lead to large-scale changes in habitat, with the area of coastal forests likely to decrease by 82%, while the area of rain-fed habitats may increase by 10–13%. In July 2020, under the influence of the El Niño phenomenon and the impoundment of dams in the tributaries of the Mekong River, the water level of the Tonle Sap Lake hit a record low for the same period in the past 60 years.
Fishery
The Tonlé Sap Lake District has always been a vital fishing and agricultural production area for Cambodia, and it has largely maintained Angkor
Angkor ( , 'capital city'), also known as Yasodharapura (; ),Headly, Robert K.; Chhor, Kylin; Lim, Lam Kheng; Kheang, Lim Hak; Chun, Chen. 1977. ''Cambodian-English Dictionary''. Bureau of Special Research in Modern Languages. The Catholic Uni ...
, the largest pre-industrial settlement complex in history. While many fish left lakes and ponds to spawn in flooded forests at the onset of floods, the inflow of Mekong floods brought large numbers of fry, which found shelter and food in flooded forests and floodplains.[
The approximately 1.2 million people who live in the Tonlé Sap Lake area, which accounts for about 60% of Cambodia's annual freshwater catch of over 400,000 tons, account for 60% of the country's population's protein intake.] Most fish are eaten fresh, and savory and fermented fish paste Prahoc is usually marinated from the least popular fish or leftover fish that cannot be sold fresh. For more than a century, the most productive lake areas have been privatized through a government-lease system of fishing grounds, providing more than $2 million in tax revenue annually.
Since Buddhism is against killing, fishermen tend to limit their catch to what they can feed their families. They do not kill the fish with their own hands but wait for the fish to die naturally after they leave the water. At the end of the rice season, people restore canoes that have been in use for hundreds of years or build new canoes when they can't be repaired in temples along the river, in preparation for the boating competition of the water festival. After two days of racing all the canoes come together to celebrate the Naga, the water serpent, who supposedly spit out the lake into the sea at the end of the rainy season, while bringing fish into the Mekong through the Tonlé Sap River.[
The area is home to many Cambodians of Vietnamese origin who live in floating villages on boats by the lake.] Most of the fishermen of Tonlé Sap Lake are of Vietnamese origin. They have lived in Cambodia for a long time and are the main suppliers of the country's fishery market. They had to flee to Vietnam during the Khmer Rouge reigning era from 1975 to 1979. Only returned after the downfall of the regime and continued to fish in the Tonle Sap.
See also
References
Further reading
* Kuenzer, C. (2013): "Field Note: Threatening Tonle Sap: Challenges for Southeast-Asia’s largest Freshwater Lake." In: ''Pacific Geographies'' 40, pp. 29–31.
* Milton Osborne, ''The Mekong, Turbulent Past, Uncertain Future'' (Atlantic Monthly Press
Grove Atlantic, Inc. is an American independent publisher, based in New York City. Formerly styled "Grove/Atlantic, Inc.", it was created in 1993 by the merger of Grove Press and Atlantic Monthly Press. As of 2018 Grove Atlantic calls itself " ...
, 2000)
External links
*
*
Australian Mekong Resource Centre
Cambodia National Mekong Committee
THE STRATEGIC SIGNIFICANCE OF THE MEKONG By: Osborne, Milton
*
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{{DEFAULTSORT:Tonle sap
Lakes of Cambodia
Biosphere reserves of Cambodia
Shrunken lakes
Tributaries of the Mekong River
Freshwater ecoregions