Irrawaddy River ecosystem

• Category: Inland Aquatic Biomes.
• Geographic Location: Southeast Asia.
• Summary: The main river running entirely through the country of Burma, the Irrawaddy is relatively undeveloped, but human activity is approaching a tipping point that could devastate species such as the Irrawaddy river dolphin.

The Irrawaddy River (Ayeyarwaddy River in Burmese) is the principal river of Burma (or Myanmar), and is the most important commercial shipping route in the country. The name Irrawaddy is believed to come from the Sanskrit word meaning elephant river. The Irrawaddy River drains most of Burma, through a region known as the Chindwin Valley, and also drains parts of India and Thailand. It originates at the confluence of the N’mai and Mali Rivers, which are fed by glacial runoff from remote mountains in the northern regions of the country and in Tibet, China. The river flows generally from north to south, emptying into the Andaman Sea area of the Indian Ocean.

The Irrawaddy River is approximately 1,350 miles (2,170 kilometers) long. Between the Burmese cities of Myitkyină and Mandalay, the Irrawaddy flows through three narrow gorges, or defiles. Its total drainage area is 158,000 square miles (411,000 square kilometers). At its mouth, the river discharges between 82,000 and 1,152,000 cubic feet (2,300 to 32,600 cubic meters) of water per second into the Irrawaddy Delta. The delta begins around 58 miles (93 kilometers) north of Hinthada; the edges of the delta are formed by the southern tip of the Arakan Mountains to the west and the Pegu Mountains to the east. The delta’s nine arms cover 26,870 square miles (69,600 square kilometers). The Irrawaddy is the fifth-most heavily silted river in the world, and this makes the delta incredibly fertile.

The Irrawaddy River embodies two climate zones: the northern sections of the river run through a humid subtropical climate, while the south passes through a humid tropical climate. Both zones are affected by the South Asia summer monsoons, which bring heavy rain from May to October. During this six-month span, the region receives between 60 and 100 inches (150 and 250 centimeters) of precipitation.

At the Burmese capital Rangoon (Yangon), in the lower half of the river, temperatures fluctuate between an average of 77 degrees F (25 degrees C) in January to 86 degrees F (30 degrees C) in June. At Myitkyina, in the upper basin of the river, the temperature averages 64 degrees F (18 degrees C) in January, and 82 degrees F (28 degrees C) in June. Temperatures decrease farther north, as altitude increases toward the glaciers that feed the rivers, averaging below 68 degrees F (20 degrees C) annually.

The Irrawaddy River passes through several cities between Myitkyinā and Rangoon. The river is Burma’s principal shipping route, as the Chindwin Valley has no railroad. In fact, the Irrawaddy has been used for transport and trade since the sixth century. Only a handful of the cities have large port facilities; the other towns can only accommodate one or two small barges at a time. It is likely the government will push to upgrade all these facilities, which will bring pressure on river habitats, but also present the opportunity to “get it right” ecologically.

Because the delta is a major rice growing area, rice is an important commodity in trade along the river. One of the Irrawaddy’s downstream tributaries, the Mu river, has been used for agriculture since the ninth century. The Mu Valley irrigation project is the largest such activity in the country, allowing for dry season growing of corn, peanuts, wheat, sesame, millet, cotton, and other dry crops. Native flora along the river ranges from hardwoods like teak, to conifer stands, swaths of bamboo, and in the delta area, extensive mangrove swamps.

Wildlife

The Irrawaddy River is home to a wide range of wildlife, including 79 known species of fish and four known endemic bird populations. New species of fish are still being discovered, including a new species of hill stream catfish. The biodiversity of the river is at risk due to human expansion, dam building, and pollution. The two species most at risk are the Irrawaddy dolphin and the Irrawaddy river shark.

The Irrawaddy dolphin (Orcaella brevirostris) is most closely related to the orca whale (Orcinus orca). It has a sparse distribution in the shallow, coastal waters of the Indian Ocean from the Philippines to northeastern India. Freshwater populations are isolated to the Irrawaddy River; Mahakam River in Indonesia; Malampaya Sound in the Philippines; the Mekong River in Laos, Cambodia, and Vietnam; and Songkhla Lake in India. Marine populations stretch from India all the way to Australia.

The Irrawaddy shark (Glyphis siamensis) is a river shark only found in the Irrawaddy River near Rangoon. There is little information on the shark; the only studied specimen was found in the late nineteenth century at the mouth of the Irrawaddy River. It exists only as a museum specimen. Though no other specimens have been found to confirm that it is not extinct, it is classified as Critically Endangered on the ICUN Red List.

Human Impact

The Irrawaddy River has its share of problems and environmental concerns. In this energy-driven age, power sources are a major commodity in the region. This river is a potential power source in which China continues to show great interest. The government in Burma put the $3.6 billion Myitsone dam project on hold in September 2011. As of March 2012, the Chinese government has been increasing pressure on Burma to restart construction. In 2024, China resumed negotiations with coup junta to try to revive the dam project. Thousands of individuals have already been displaced from various small villages and farmland surrounding the river. The implications of blocking the river are far-reaching for local populations and the environment. Besides the displacement of thousands of people, harm to local fish and dolphin populations, damming would have a large impact on water flow through the delta, and therefore to delta agriculture.

Another current environmental concern comes from overzealous gold mining along the banks of the river. Mercury and cyanide are both harmful byproducts of blasting for gold. This, and oil leaking from the boats that run along the river, badly disrupt the ecosystem, killing off both fish and dolphins and causing serious health problems for people living in nearby villages.

Finally, local fisherman use methods that can be harmful to wildlife. Electrode-fishing is a method utilizing an electrode to run a high voltage current through the water, paralyzing or killing fish. The fish then float to the surface, where they are netted. Dolphins also fall prey to the current. Another method involves the use of gill nets; some dolphins, usually young calves, become trapped in the nets, where they soon drown. Overfishing also can deplete fish populations, causing drastic and negative effects on the food chain.

In 2011, local governments, environmental and human rights groups managed to suspend construction of the Myitsone dam project. Burmese activists feared that if the dam project moved forward, its impact would extend to communities downstream that rely on the river flow and adequate nutrients to sustain the rice production on which the country depends. Meanwhile, the Chinese and the China Power Investment Corporation are pressuring the Myanmar government to resume construction of the dam since companies have already invested heavily in the project.

Climate change is anticipated to significantly alter river's ecosystem. The global mean surface temperature of the river is projected to increase 0.3 degrees to 0.7 degrees C from 2016 to 2035. Extreme storms, heavy rainfall, and severe drought will affect the river's ecosystem. Experts are concerned about a reduction in sediment, which may alter the flow of the river and decrease its depth.

Bibliography

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"Myanmar Mulls Options to Keep Suspended Chinese Dam Project Alive." Radio Free Asia, 30 Jan. 2019, www.rfa.org/english/news/myanmar/myanmar-mulls-options-01302019174902.html. Accessed 26 Nov. 2024.

Sirisena, T.A.J.G. et. al. "Climate Change and Reservoir Impacts on 21st-Century Streamflow and Fluvial Sediment Loads in the Irrawaddy River, Myanmar." Frontiers in Earth Science, 23 Mar. 2021, doi.org/10.3389/feart.2021.644527. Accessed 26 Nov. 2024.

Smith, Brian D., and Randall R. Reeves. “River Cetaceans and Habitat Change: Generalist Resilience or Specialist Vulnerability?” Journal of Marine Biology 2012, no. 1 (2012).

Smith, Jeff. “Two Rivers: The Chance to Export Power Divides Southeast Asia.” National Geographic Daily News, 25 Oct. 2011, www.nationalgeographic.com/science/article/111026-mekong-irrawaddy-hydropower-dams. Accessed 26 Nov. 2024.

Thant, Mynt-U. Where China Meets India—Burma and the New Crossroads of Asia. New York: Farrar, Straus & Giroux, 2012.