Tonlé Sap wetlands
The Tonlé Sap wetlands, located in central Cambodia, encompass Southeast Asia's largest freshwater lake and its extensive floodplain, covering approximately 27,027 square miles (70,000 square kilometers). Known for its rich biodiversity, the region has been recognized as a UNESCO Biosphere Reserve, highlighting its ecological significance, cultural heritage, and economic importance. This unique ecosystem experiences pronounced seasonal fluctuations in water levels, with the lake expanding significantly during the rainy season and contracting in the dry season, resulting in diverse habitats that support a wide range of plant and animal species.
The Tonlé Sap wetlands are home to around 200 plant species and approximately 225 bird species, including several that are globally threatened. The lake is vital for fisheries, contributing over half of Cambodia's freshwater fish catch, which supports the livelihoods of about 3 million people. Human activities, including fishing, rice cultivation, and urban expansion, have placed enormous pressure on this ecosystem, leading to habitat loss and pollution. Conservation initiatives, such as the establishment of fish sanctuaries, aim to protect the area, but ongoing efforts are necessary to ensure its sustainability in the face of challenges like climate change and overexploitation.
Subject Terms
Tonlé Sap wetlands
Category: Inland Aquatic Biomes.
Geographic Location: Asia.
Summary: Characterized by annual climatic changes and hydrological fluctuations, these wetlands form a unique ecosystem that has great economic, social, environmental, and cultural significance.
Located in central Cambodia, the Tonlé Sap, or Great Lake, is the largest freshwater lake in Southeast Asia. The lake’s drainage basin includes many major tributaries and covers almost 27,027 square miles (70,000 square kilometers). Its low-lying floodplain extends up to 186 miles (300 kilometers) and spans up to 62 miles (100 kilometers) in width.
The Tonlé Sap and its surrounding wetlands are rich in biodiversity and have been recognized by both local and international organizations as a unique ecosystem with significant economic, social, environmental, and cultural value. In October 1997, Tonlé Sap and parts of its floodplain were nominated as a Biosphere Reserve under the Man and the Biosphere Program of the United Nations Educational, Scientific, and Cultural Organization (UNESCO). This was followed by a Cambodian Royal Decree in April 2001 that officially established the Tonlé Sap Biosphere Reserve. The area is to serve various functions, including fostering sustainable development, providing support for projects and education, and conserving biological diversity.
The Tonlé Sap wetlands are characterized by annual climatic changes and hydrological fluctuations that make this ecosystem a unique ecological phenomenon. The area is subject to a tropical monsoon climate, with distinct dry and rainy seasons. As a result, the Tonlé Sap expands and contracts seasonally following precipitation patterns.
The hydrological fluctuations also cause the flow of the Tonlé Sap to reverse twice a year. During the dry season, water flows out from the Tonlé Sap to the Mekong River. However, during the rainy season, the flow direction reverses, due to large volumes of rainwater entering the Mekong, and water flows back from the Mekong into Tonlé Sap.
The lake volume can fluctuate significantly, from 0.3 cubic miles (1.3 cubic kilometers) during the dry season to as much as 17 cubic miles (70 cubic kilometers) during the wet season—with its depth increasing from 3 to 33 feet (1 to 10 meters). At the peak of the wet season, the lake is estimated to cover up to 8 percent of the land area of Cambodia, as its surface area expands from 965 square miles (2,500 square kilometers) to 6,178 square miles (16,000 square kilometers).
Biodiversity
The annual flood pulse, nutrient cycling, and high sediment fluxes in the Tonlé Sap wetlands support the survival and proliferation of many species of vegetation and wildlife, making the Tonlé Sap ecosystem one of the most productive inland waters in the world. The area is home to approximately 200 plant species, many of which have adapted to withstand significant water-level fluctuations. Many of these flora species are found exclusively in the Tonlé Sap wetlands, that is, they are endemic to the biome. The vegetation in the area includes aquatic herbaceous communities, seasonally flooded freshwater swamp forests, and dense short-tree shrublands.
The Tonlé Sap Wetlands habitat also supports close to 50 species of mammals and more than 40 species of reptiles and amphibians, including globally threatened species such as the long-tailed macaque, Germain’s silver leaf monkey, Siamese crocodile, and yellow-headed temple turtle. The lake and its wetlands also form an important breeding, nesting, and feeding site for birds. About 225 bird species have been observed, including globally threatened species such as the spot-billed pelican and black-headed ibis.
Out of all the freshwater systems of the world, the Tonlé Sap wetlands support the greatest known biodiversity of snails. Other invertebrates, such as crabs, shrimp, and more than 200 species of insects, have also been found in the area.
In terms of biomass and species diversity, fish represent the largest and most important vertebrate faunal group in the Tonlé Sap wetlands. The area yields about 197,865–271,169 tons (179,500–246,000 metric tons) of fish annually, accounting for more than half of all freshwater fish catches in Cambodia and providing food for more than 3 million people. Due to the unique fluctuating hydrological patterns of the Tonlé Sap ecosystem, many of the fish species in the area migrate laterally within the ecosystem itself or longitudinally to the Mekong. Globally threatened fish species, such as the Mekong giant catfish and Jullien’s golden carp, have been found in Tonlé Sap.
Human Activity and Conservation Efforts
Tonlé Sap and its wetlands also support a huge human population. The lake has played a significant role in shaping Khmer history and culture. It is believed that Tonlé Sap helped the Khmer Angkor civilization thrive, and many traditions and festivals still revolve around the lake. Currently, an estimated 470,000 people live within the lake’s inundation zone, and more than 3 million people live in the immediate surroundings of Tonlé Sap and its wetlands.
About 80,000 people live in 170 floating villages on the lake itself. The villages range in size from two to 100 households. The people living on and in the periphery of the Tonlé Sap depend heavily on its natural resources for survival. The lake is responsible for about 75 percent of Cambodia’s inland fish catch each year. The main economic activities of the Tonlé Sap communities include fishing, rice cultivation, and wood collection.
The Tonlé Sap ecosystem has been significantly affected by the large volume of human activity in the area. Overhunting and overfishing of animals have resulted in the extirpation of many species here, such as the Irrawaddy dolphin and the greater flamingo. Significant amounts of vegetation have been destroyed by human activity, such as through the conversion of animal habitats for rice cultivation.
Pollution is also prevalent in the area, especially through excessive noise, use of agrochemicals and petrochemicals, and unregulated release of untreated urban and domestic waste. Climate change impacts in the area may include greater than normal areas of flooding and more prolonged flooding.
Conservation efforts have been undertaken by various organizations to protect the Tonlé Sap ecosystem. Eight designated fish sanctuaries have been established in the reserve, which prohibit fishing and boat entry during the dry season. However, more needs to be done to promote conservation and ensure that human activity in the area does not result in irreversible long-term effects to this unique and important ecosystem.
Bibliography
Bunnara, Min and Cornelis van Tuyll. Case Study: Tonle Sap Biosphere Reserve. Phnom Penh, Cambodia: MekongInfo, 2000.
Davidson, Peter J. A. The Biodiversity of the Tonle Sap Biosphere Reserve: 2005 Status Review. Phnom Penh, Cambodia: Wildlife Conservation Society, Cambodia Program, 2006.
“Local Communities.” Wildlife Conservation Society, 2021, cambodia.wcs.org/Wild-Places/Tonle-Sap-Lake-Floodplain/Local-Communities.aspx. Accessed 29 Aug. 2022.
Matsui, Saburo, et al. Tonle Sap: Experience and Lessons Learned in Brief. Kasatsu, Japan: International Lake Environment Committee Foundation, 2006.