Amu Darya River

Category: Inland Aquatic Biomes.

Geographic Location: Asia.

Summary: The Amu Darya is the longest river in central Asia. Its lower reaches have been so negatively affected by human engineering that it now can be regarded as an ecological tragedy.

The Amu Darya is one of the most iconic rivers of the Old World, shimmering like the Nile, Euphrates, and Tigris Rivers. Known to the Greeks as the Oxus and to the Arabs as the Gihon or Jeihoon (one of the four rivers of paradise), the Amu Darya rushes down from the high peaks of the Pamir, Hindu Kush, and Alayskiy mountains—all part of the western portion of the Himalayas—and gently flows in a northwesterly direction through the central Asian lowlands toward the Aral Sea, which was the world's fourth-largest inland sea before it was strangled in recent decades by irrigation dams, canals, and reservoirs. Its sister river, Syr Darya, flows on a course roughly parallel to the Amu but drains a much smaller volume of water into the northern section of the sea.

Human beings have lived along both rivers for more than 3,000 years. Alexander the Great, Zoroaster, Genghis Khan, and the Russian czars spent considerable time exploring these environs at a time when they were least transformed by culture. The ecoregions within the desert biome that set the conditions that give life to the Amu Darya have changed dramatically, and so have the long-term ecological characteristics defining this once-celebrated river.

The Darya (the Persian word for river) emerges within a dry and desert biome, which is subdivided into eight large-scale ecoregions. The 1,600-mile-long (2,575-kilometer-long) Amu, named after the medieval city of Amul, has a drainage basin of 193,051 square miles (500,000 square kilometers) that joins three of these regions: Tropical/Subtropical Desert Altitudinal Zone, Tropical/Subtropical Steppe Altitudinal Zone, and Temperate Desert Province Mid-Latitude. The climate and landforms of each region enable certain kinds of plants and animals to thrive, including those in rivers, seas, and other water bodies. It is this interrelationship that defines the biogeography of the Amu Darya, yet human cultures' participation in this relationship should be emphasized to understand the present ecological condition of the river.

Although the location of the source of the Amu Darya is debatable, most geographers agree that the river begins at the confluence of the Pandj and Vakhsh Rivers, on the southwestern border of Tajikistan. These tributaries, along with others joining the main channel, flow from the highest reaches of the western portion of the Himalayas in what is called a Tropical/Subtropical Desert Altitudinal Zone, where melting alpine glaciers and snow provide up to 80 percent of the Amu's water. This cold, arid, high-altitude region has little vegetation, mainly lichens and mosses that grow on boulders and rocks. Shrubs, herbaceous plants, and grasses can flourish within the region, but at lower altitudes and often in small patches. Meadows form; trees such as juniper and poplar take root at still lower altitudes. In the vicinity of the confluence of the Amu's major tributaries, where the average height of the mountains has decreased significantly and the general location of the Amu and its tributaries trends slightly southward, the river becomes part of the Tropical/Subtropical Steppe Altitudinal Zone. The transition is almost imperceptible.

Dam Construction

The rivers of the altitudinal regions move swiftly, from high peaks to low, through Afghanistan, Kyrgyzstan, Tajikistan, and Uzbekistan, cutting V-shaped valleys into the landscape. Such natural architecture offers an ideal setting for the construction of dams for hydroelectricity, agricultural irrigation, and flood prevention. Because the economies of the altitudinal regions depend deeply on local agriculture, the water of the Amu is a precious resource and, therefore, a cause of contention. The building of dams anywhere in the mountain drainage basin—a surface area that constitutes about half the total area of the basin—is the most contentious issue.

By the end of the 20th century, a network of dams had been built across the Amu, but mostly beyond the mountains. During the era when most of central Asia was under the control of the Soviet Union, however, the tallest of these dams—in fact, the tallest in the world at 984 feet (300 meters)—was erected on the Vakhsh River at Norak (Nurek), Tajikistan. Another hydroelectric dam, the Rogan project, was in the works on the same river until the fall of the Soviet Union. Now an independent Tajikistan intends to complete the project, and if successful, Rogan would be the tallest in the world. Yet as global warming reduces Himalayan glaciers, populations in host countries are increasing, and so is the demand for water.

Eventual peace in war-torn Afghanistan, a country that contributes more water to the Amu than any other, will also place heavy demands on the river as restarted economic development will carry the need for hydropower, irrigation, and drinking water. For these reasons, governments including that of Turkmenistan are attempting to negotiate an arrangement that promotes fair and sustainable use of the river. If unsuccessful, these countries will lose more than the riverine political boundaries that separate them.

Desert Region and Evaporation

If the altitudinal ecoregions are the source of water nourishment, the temperate desert region is the grounds for depletion not only of water, but also of the river's biodiversity. When it reaches the temperate desert, where differences in seasonal temperatures can be extreme and water bodies turn to ice during the winter, the Amu becomes one of the world's most turbid rivers, suspending a high amount of sediment scraped from high-mountain-valley walls by the intense force of the river system's currents. Gradually, as the drainage basin levels, the Amu's current slows, and the channel not only becomes wider, but also divides and braids as deposition of sand and silt creates numerous intermittent islands, ponds, and lakes. The constant shifting of alluvium deposition makes the river hardly navigable. Endemic fish species, however, such as the Amu Darya sturgeon and its much smaller cousin, the shovelnose sturgeon, both of the caviar kind, still ply these muddy waters. Their presence, however, like that of other fish species (namely pike, trout, and roach), is becoming less evident.

Since the mid-20th century, evaporation, irrigation, and infiltration have been the primary influences on the life of the river. As the Amu flows toward and through the Kyzyl Kum and Kara Kum deserts, an area that receives about 2,500 to 3,000 hours of sunshine and less than four inches (10 centimeters) of rainfall annually, much of its water evaporates into the atmosphere. The barrage of dams, canals, and reservoirs diverts the channels mainly for irrigation of cultivated land. Earlier, the Soviets realized their goal of making central Asia one of the largest cotton-producing regions in the world, but they did so with unsustainable technology and practices. Canals seeped water, and the resulting flooding of large swaths of desert not only increased evaporation—thus turning floodplain and desert into infertile salt flats—but also layered the surface with agrochemicals that contaminated and grossly changed the Amu's biota.

Tugai Forests

The influences of flooding and agrochemical contamination together have had a devastating effect on one of the most unique riparian ecosystems in the world: the Tugai forests. In the temperate desert region of central Asia, these deciduous forests are like oases lining the banks of rivers and narrowly expanding across floodplains. Trees such as willows, buckthorn, poplars, oleasters, and tamarix are stabilizers around which grow lianas, as well shrubs such as briar roses and honeysuckles. Interspersed throughout are herbaceous meadows, tussocks of reeds, and meadow-swamp wetlands.

These verdant sanctuaries are habitats for mammals including the dormouse, badger, wild boar, jackal, Tolai hare, and tamarix gerbil. Less common are the otter, Bukhara deer, hyena, and goitered gazelle. The Caspian tiger, once positioned at the apex of the food chain, has not been seen for more than 50 years. Among common amphibians and reptiles are the Anatolian frog, central Asian cobra, Caspian turtle, and Turkestan gecko. Common birds of the Tugai are shikra, pheasant, scops owl, kestrel, penduline tit, and cuckoo. In wetland ecosystems, common species are the pelican, cormorant, heron (with the rarer aquatic species being gulls), white-headed duck, marbled teal, and flamingo. The wetlands offer temporary accommodations for more than 150 species of birds, most flying in from Kazakhstan and western Siberia to winter, nest, or rest and recoup before migrating onward.

At the beginning of the 20th century, the gallery-like forests along the Amu Darya once covered an area of around 200 square miles (518 square kilometers). At the beginning of the 21st century, all that remained was 20 square miles (52 square kilometers), and in that area, only a few forests are intact and flourishing.

Water pollution and depletion have dramatically changed the habitat and the river's ecosystem to the point where both are now nearly devoid of their most common denizens: birds and fish, respectively. At present, just two percent of the forest along the Amu is protected in several small preserves, the largest of these being the Badai-Tugai and Kyzyl-Kum Reserves, both in Uzbekistan.

Tugai forests, reed jungles, lush lakes and bogs, and swamps enclosed between sand dunes were once characteristic of the distributaries that formed the Amu Delta. Salt- and drought-resistant plants now dominate the dry and gritty landscape, which is deflating for lack of water. Of the 178 animal species that have evolved with this ecosystem, only 38 have survived the recent rapid changes imposed on this ecoregion.

The mid-latitude westerly winds still blow over the delta and Aral Sea, but they offer little moisture for the thirsty winds that have always carried water across the deserts and into the majestic Himalayas, where it falls as rain and snow, streams into the upper Amu and its tributaries, and then begins its journey back to the sea. The winds are drier now, carrying salt and pesticides. The shimmering Oxus no longer reaches the sea.

Bibliography

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Shahgedanova, Maria. The Physical Geography of Northern Eurasia. Oxford, UK: Oxford University Press, 2003.

Veregin, Howard. Rand McNally. Goode's World Atlas. 22nd edition. Upper Saddle River, NJ: Prentice Hall, 2009.

Zheng, Wang, et al. "Analysis of the Water Demand-Supply Gap and Scarcity Index in Lower Amu Darya River Basin, Central Asia." International Journal of Environmental Research and Public Health, vol. 19, p. 743, doi.org/10.3390%2Fijerph19020743. Accessed 17 Jul. 2022.