Mekong River

• Category: Inland Aquatic Biomes.
• Geographic Location: Southeast Asia.
• Summary: Development along the 12th-longest river in the world has been slow, therefore sparing the region’s extraordinary biodiversity, but global economic pressures loom.

The biodiversity of the Mekong River and its drainage basin is almost incomparable. Only the Amazon River’s richness of plant and animal life outshines that of southeast Asia’s longest river. The Mekong’s eccentricity sprouts from the various ecosystems that it simultaneously creates and flows through. The river’s name comes from Mae Nam Khong, meaning the “mother of water.”

Up until the end of the 20th century, the river went mostly unhindered by human engineering, including the machinery of modern warfare, particularly that of the Second Indochina (or Vietnam) War, which exacted a heavy toll on the people and environment of mainland southeast Asia but largely spared the river’s contours and bedrock, along with most of the basin’s ecology. Today, as the world extols the virtues of the global marketplace, the economic dragons and tigers of Asia expect the Mekong to nurture regional development and generate financial wealth. While this is happening, the river and its surroundings are changing.

Biodiversity and Human Impact

Because the Mekong flows some 2,600 miles (4,200 kilometers) and generally from north to south, the Mekong region contains myriad ecosystems formed by an immense variety of flora and fauna: about 20,000 species of plants, 1,200 species of birds, 800 species of reptiles and amphibians, and 430 species of mammals, all specific to local types of terrain, temperature, precipitation, and drainage patterns.

The river joins five biomes that spread across parts of southeast Asia: Tropical Savanna, Tropical Savanna Altitudinal Zone, Tropical Rainforest, Humid Subtropical Altitudinal Zone, and Tropical/Subtropical Steppe Attitudinal Zone, all within the broader category of Humid Tropical. Although the classification of biomes depends on natural and geophysical circumstances, the river’s massive fan-shaped delta, unfolding into the South China Sea, has been so transformed by culture that this particular area of the river could now be classified as an Anthropogenic biome.

Carved into the delta are canals and irrigation ditches controlling the flow of the river and dividing its fresh waters among the intensively cultivated paddies, plantations, and fish ponds that, when seen from above, create a mosaic of distinctly human layout. With intensive agriculture comes high population density, which in turn gives birth to cities. Small wonder that one of the first recorded empires of southeast Asia—the Funan—arose from the nutrient rich soils of this plain, which now reaches all the way to Phnom Penh, the capital city of Cambodia. Ho Chi Minh City, Vietnam, sits more toward the end of the lines where sand, silt, and other sediments that have broken away from the 309,000-square-mile (800,000-square-kilometer) drainage basin reach the sea. Here, where freshwater encounters salt, were once thick mangrove forests.

Moving upstream away from the coast (as sometimes seawater does with devastating consequences on agricultural land), the Mekong remains within the Humid Tropical Zone but leaves the Tropical Rainforest of evergreen broadleaf trees, often hosting epiphytes and embracing lianas, to enter a Tropical Savanna region. Unlike the forest—which teems with wildlife including the Asian elephant, Siamese crocodile, leopard cat, agile gibbon, king cobra, Asian emerald cuckoo, sun bear, and Indochinese tiger—the savanna has an annual wet and dry season, a climate regime referred to as monsoon. Less overall rainfall yields a landscape covered with tall grasses, including bamboo, and interspersed with deciduous trees.

Tonlé Sap, the Great Lake of Cambodia, straddles these biomes; and though the Mekong curves around the lake, its tributaries with their cargo of sediment and biota shape the intricate ecology of the area, much of which has been designated a United Nations Educational, Scientific and Cultural Organization (UNESCO) Biosphere Reserve. Farmers and fisherman also rely on Mekong replenishment; they have done so here since the dawn of Angkorian civilization, the last of the great Indianized empires of southeast Asia.

Never-Tamed Stretches

More than 1,000 miles (1,600 kilometers) above the Great Lake, the Mekong begins its flow from the upper portion of a drainage seated in the Tibetan Plateau, the highest region in the world. It is the upper basin that makes the length of the Mekong notoriously un-navigable. The bedrock—raised, twisted, and folded by the tectonic foundation of the Indian subcontinent pushing toward the northeast—lines the river with rapids and waterfalls, and also supplies the contrastingly flat lower basin with half of its alluvium. On the basin plain live most of the 70 million people inhabiting the Mekong region, and in the lower course of the river, the largest collection of giant fish species in the world, including the giant Mekong catfish that can reach 9 feet (3 meters) in length. It is in the lower reaches, too, where the famous dugong or river dolphin is found.

Where the Mekong flows out of higher lands, the basin begins to narrow and biomes transition into Tropical Savanna Altitudinal Zone. This upper basin’s biomes are altitudinal, meaning that differences in land elevation are prime influences on the biotic and abiotic characteristics. For instance, as elevation increases, average temperatures decrease—and generally so does biodiversity. The difference in elevation between the source of the Mekong in the Tibetan Plateau and the mouth of the river in the delta is approximately 15,000 feet (4,500 meters). At one end is an evergreen rainforest, or, rather, an anthropogenic biome 10 percent of which is covered by old growth forest; in the middle, deciduous and coniferous trees and bushes in the savanna; and at the other end, a rocky desert of ice sheets, alpine glaciers, and orographic (mountain-created) rainfall—the true mother of waters in the Mekong.

Through the rugged mountains of China’s Yunnan province, the Mekong, Salween, and Yangtze Rivers etch parallel gorges that UNESCO has designated a natural heritage site. Below, the pristine gorges give way to hydroelectric dams. Since this region contributes only 15 to 20 percent to the Mekong’s water volume, the dams’ effect on water supply downstream is tolerable, except when the wet monsoon disappoints. Water held up by dams on many of the Mekong’s tributaries also makes dry spells worse for those depending on the river for their livelihood. Fluctuating water levels, typical of dammed-up river systems, disrupt traditional trade and transport networks, and the corresponding increase in water temperature is responsible for a recent rapid decrease in aquatic species in the Tonlé Sap and in other internationally recognized eco-preserves.

The mainstream section of the Mekong in southeast Asia remains free of dams. Even so, river traffic tends to be localized, leaving long stretches of the river undisturbed by barges, boats, or shoreline development. Few sturdy roads line the banks and fewer bridges connect them; many backwater ports seem more like simple docks. But this may all change soon as China, India, Japan, and even the United States design a future for the region that will, they promise, expand river-based economies, increase standards of living, and integrate the nations of the region: China, Burma (Myanmar), Laos, Thailand, Cambodia, and Vietnam.

However, for such economic dreams to become reality, far more of the length of the Mekong will have to become navigable and also supply a source of electricity. Blasting away river banks, rapids, and waterfalls to make room for ships, dams, bridges, and ports would only be the beginning of a long process that may recast all of the Mekong as a biome. The Mekong River Commission, founded in 1995 to promote sustainable development and scientific management of the Basin, hopes to prevent the negative aspects of this from happening.

Threats

The Mekong River has managed to withstand large dam infrastructure, overfishing, and sand mining. Recent dam construction and the promise of further development has created a looming threat, particularly to water levels. Many experts identify hydropower dams as the biggest threat to the Mekong river and its tributaries. The dams block nutrient-rich sediment from traveling down river. In Vietnam, farmers are watching land being washed away as a consequence of the lack of sediment and an effect of erosion. Dredging of the river further exacerbates the problem of erosion, starving the river of the sediment needed to maintain the natural balance of the ecosystem.

However, droughts caused by global warming have created an environmental crisis. In 2019, the monsoon rains did not arrive as usual in May, and the Mekong dropped to its lowest level in 100 years. When the monsoon rains finally did arrive, they did not last as long as usual. By 2020, some parts of the river had nearly dried up and the water has changed color because of algae. The fish in some areas are emaciated and can only be used to feed other fish. A 2024 report painted a bleak picture, stating parts of the river were on the verge of collapse and one-fifth of the fish in the river faced extinction. Experts fear that the river may be at its breaking point, and the people who depend upon it for their livelihood may be in trouble. This is especially true of severe drought continues to affect the river.

Bibliography

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