Tonlé Sap
NASA satellite image
Coordinates	12°53′N 104°04′E / 12.883°N 104.067°E / 12.883; 104.067Coordinates: 12°53′N 104°04′E / 12.883°N 104.067°E / 12.883; 104.067
Primary outflows	Tonle Sap River
Basin countries	Cambodia
Surface area	2,700 km² (normal) 16,000 km² (monsoon)

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Tonle Sap lake seen from Phnom Bakheng.

The Tonlé Sap (Khmer: ទន្លេសាប IPA: [tunleː saːp], "Large Fresh Water River", but more commonly translated as "Great Lake") is a combined lake and river system of major importance to Cambodia.

The Tonlé Sap is the largest freshwater lake in South East Asia and is an ecological hot spot that was designated as a UNESCO biosphere in 1997.^[1]

The Tonlé Sap is unusual for two reasons: its flow changes direction twice a year, and the portion that forms the lake expands and shrinks dramatically with the seasons. From November to May, Cambodia's dry season, the Tonlé Sap drains into the Mekong River at Phnom Penh. However, when the year's heavy rains begin in June, the Tonlé Sap backs up to form an enormous lake.

Map of Tonle Sap Lake and its floodplain

Scenery, overlooking the lake

Seasonal direction of flow[link]

For most of the year the lake is fairly small, around one meter deep and with an area of 2,700 square km. During the monsoon season, however, the Tonlé Sap river, which connects the lake with the Mekong river, reverses its flow. Water is pushed up from the Mekong into the lake, increasing its area to 16,000 square km and its depth to up to nine meters, flooding nearby fields and forests. The floodplain provides a great breeding ground for fish.

The pulsing system with its large floodplain, rich biodiversity, and high annual sediment and nutrient fluxes from Mekong makes the Tonlé Sap one of the most productive inland fisheries in the world, supporting over three million people and providing over 75% of Cambodia's annual inland fish catch and 60% of Cambodians' protein intake. At the end of the rainy season, the flow reverses and the fish are carried downriver.

Water dwelling on the lake of Tonle Sap near Siem Reap.

National Highway 6A crosses the Tonle Sap river in Phnom Penh

Sedimentation[link]

National and local observers often state that the Tonlé Sap Lake is rapidly filling with sediment. However, recent long-term sedimentation studies show that net sedimentation within the lake proper has been in the range of 0.1-0.16 mm/year since circa 5,500 years before present (BP) and hence there is no threat of the lake filling up with sediment. The nutrients bound to suspended sediments are important for the Tonle Sap system, particularly to maintain its long-term sustainability.^[2]

The reversal of the Tonlé Sap river's flow also acts as a safety valve to prevent flooding further downstream. During the dry season (December to April) the Tonlé Sap Lake provides around 50% of the flow to the Mekong Delta in Vietnam.

The lake occupies a depression created due to the geological stress induced by the collision of the Indian subcontinent with Asia. In recent years, there have been concerns from scientists about the building of high dams and other changed hydrological parameters in Southern China and Laos that has threatened the strength and volume of the reverse flow into Tonle Sap, which in turn decreases nesting, breeding, spawning, and feeding habitats in floodplain, which results in adverse impacts on fish productivity and overall biodiversity.^[3]

Biosphere reserve[link]

The Tonle Sap Lake and its surrounding provinces are part of the Tonle Sap Biosphere Reserve. There are nine provinces that are part of the Tonle Sap Biosphere Reserve. These are Banteay Meanchey, Battambang, Kampong Chhnang, Kampong Thom, Preah Vihear, Pursat, Siem Reap, Otdar Meanchey, and Krong Pailin.^[4]

The Preak Toal Bird sanctuary in the lake is known to be home to large colonies of spot billed pelicans, oriental darter, painted stork and greater adjutant stork.

People and culture[link]

A dwelling at the side of the lake

The area is home to many ethnic Vietnamese and numerous Cham communities, living in floating villages around the lake.

References[link]

Further Reading[link]

• Milton Osborne, The Mekong, Turbulent Past, Uncertain Future (Atlantic Monthly Press, 2000) ISBN 0-87113-806-9

External links[link]

Wikimedia Commons has media related to: Tonlé Sap

• Tonle Sap Biosphere Reserve : Environmental Information Database
• THE STRATEGIC SIGNIFICANCE OF THE MEKONG By: Osborne, Milton
• Washington Post
• Country Profile
• International Journal of Water Resources Development - Tonle Sap Special Issue
• Tonle Sap Modelling project (WUP-FIN) under Mekong River Commission
• Protected areas in Cambodia

v t e Provinces of Cambodia Provinces Banteay Meanchey Battambang Kampong Cham Kampong Chhnang Kampong Speu Kampong Thom Kampot Kandal Koh Kong Kratié Mondulkiri Oddar Meancheay Pursat Preah Vihear Prey Veng Ratanakiri Siem Reap Stung Treng Svay Rieng Takéo Municipalities Kep Phnom Penh Sihanoukville (Kampong Som) Pailin

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Leafhoppers and ants feed here off plant sap

Sap of pine

Sap is a fluid transported in xylem cells (tracheids or vessel elements) or phloem sieve tube elements of a plant. The xylem cells transport water and nutrients throughout the plant.

Xylem sap consists primarily of water, with hormones, mineral elements and other nutrients dissolved in it. Transport of sap in xylem is characterized by movement from the roots toward the leaves. Over the past century, there has been some controversy regarding the mechanism of xylem sap transport; today, most plant scientists agree that the cohesion-tension theory, along with evapotranspiration best explains this process.

Phloem sap consists primarily of water, with sugars, hormones, and mineral elements dissolved in it. It flows from where carbohydrates are produced or stored to where they are used. The pressure flow hypothesis proposes a mechanism for phloem sap transport.

Sap droplets of Sansevieria trifasciata

Maple syrup is made from reduced sugar maple xylem sap. It is often from the Sugar Maple, or Acer saccharum. In some countries (e.g., Russia, Latvia, Estonia or Finland) it is common to collect the early spring sap of birch trees (so called "birch juice") for human consumption; the sap can be used fresh or fermented and contains xylitol.

See also[link]

• Latex
• Resin

Wikimedia Commons has media related to: Plant sap

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