Boundaries

The Middle Amu Darya ecoregion includes the basin of the Amu Darya from the former upper border of its delta (just south of the town of Urgench, Uzbekistan) upstream to the lower reaches of the Surkhandarya [Surkhondaryo] River, Kafirnigan [Kofarnihon] River, and Vakhsh and Kunduz [Qonduz] rivers. It also includes the lower Zeravshan (dowmstream from Pendzhikent [Panjikent]), lower Tedzhen [Tedjen = Hari Rud], and Murghab rivers, as well as the rivers of the northern spurs of Kopet-dag Ridge and the Karakumskiy Canal system.

The western border of the ecoregion (Turan Plain [450]) follows the 60° N meridian and, north of the town of Tedzhen, Turkmenistan, turns sharply to the northwest from the lower Tedzhen=Tedjen=Hari Rud and Murghab rivers. The northwestern elongation of the ecoregion includes the Karakumskiy Canal along the northern slopes of the Kopetdag Range. In the south, the border with the Upper Amu Darya [631] runs along the northern spurs of the Badkhyz Hills and the Karabil’ Hills,  and extends to the lower Panj and Vakhsh rivers in the southeast. The ecoregion also includes the plains of the lower Vakhsh, Kafirnigan [Kofarnihon], and Surkhandarya [Surkhondaryo] rivers. The border moves northward along the Chakchar Range up to Penjikent on the Zeravshan River, and along the Kyly River to lakes Tuzkan and Aidar. The ecoregion boundary includes the Bukantau Mountains and the Mynbulak Depression, and crosses the former delta of Amu Darya [Amudaryo = Amudar’ya = Dar’yoi Amu = Darya’-i Amu] south of Urgench (the border with 629).

Freshwater habitats

A characteristic feature of the Amu Darya valley around the confluence of the Pyandzha and Vaksha rivers up to Kerki is the presence of lake-like extensions. The floodplain of the river is covered by tugais (riparian forests), dense thickets of reeds, and numerous lakes and swamps. The river channel is split into anabranches with numerous islands. From Kerki up to the Ildzhik Narrow, the width of the Amu Darya valley fluctuates from 4 km to 25 km. Slight slopes of the valley gradually merge with the surrounding terrain. Between the Ildzhik and Tyuya-Muyun narrows the character of the valley changes. The river flows through bedrock represented mostly by a thick layer of sand and loose sandstones of the Tertiary Age. Here, the valley has steep, abrupt slopes 10-20 m high, and the Kyzyl Kumy and Kara Kumy deserts are nearby. Downstream from the Tyuya-Muyun Narrow, the valley of the Amu Darya widens to several dozen kilometers, narrowing only near the Dzhumurtau and Takhia-Tash narrows. In that part of the river the maximum number of cultivated lands are concentrated, irrigated by the largest irrigation systems.

The maximum water flow occurs in the spring and early summer, and minimum flow occurs in late summer to winter. Many rivers dry up along sections of their course or are reduced to isolated pools during the minimum-flow period. This natural condition is aggravated by water extraction for irrigation and other purposes; rivers tend to disappear before reaching their principal river or lake.

The Amu Darya ranks among the largest rivers on earth in its amount of suspended alluvium. The mean annual turbidity near Kerki is equal to 3.6 kg m^-3. The maximum amount of suspended alluvium is observed in May. From June its amount diminishes reaching its minimum in November – December.

The drying of the Aral Sea has been accompanied by a profound degradation not only of its own ecological system (ecoregion 629), but also of those neighboring it. The ecological degradation became especially critical south of the Aral Sea, in the lower reaches of the Amu Darya. This was the direct impact of water resource manipulation through the construction of dams and barrages and diversion of water for predominantly irrigation use. There has been a change in fish stocks of the major rivers, with sturgeon, shovelnose, and Aral trout virtually disappearing from them. While formation of reservoirs provided new environments for lacustrine fish species, these had to be introduced, largely from East Asia. Pollution through agrochemical inputs has caused a major problem, especially in the drainage-fed water bodies, where most of the fish are declared unsuitable for human consumption. Between 1960 and 1989 the Amu Darya’s average salinity increased from 540 mg/l to 1,161.2 mg/l, with 856.6 mg/l measured in 1990. The chemical character of the Amu Darya water has changed from calcium-carbonate dominated to sodium or potassium chloride dominated, with sulphate domination of anions. The river is contaminated by phenols, oil products, heavy metals, pesticides, and nitrogen compounds. The lakes that receive drainage waters are also undergoing a process of gradual increase in water salinity, which eventually makes the environment unsuitable for the great majority of freshwater fish species.

The impact of water uptake for irrigation from the Amu Darya can be followed by the total annual discharges, as measured between 1959-1992 in the middle course at Kerki, and in the mouth of the Amu Darya at Kzyljar. Before the full development of the irrigation system the irreversible uptake was about 25 km³/year. This has markedly increased since 1970 with the annual uptake reaching 50 km³/year, or even more. In some years, no water from the Amu Darya reached the Aral Sea.

Terrestrial habitats

The ecoregion is located in desert and steppe throughout most of its range, as well as piedmont.

Description of endemic fishes

Dwarf sturgeon (Pseudoscaphirhynchus hermanni), also known as Amu Darya shovelnose sturgeon, is an endemic of the Amu Darya River, primarily in its lowland section. It attains a maximum length of 27.5 cm, and is a typical inhabitant of wide, turbid, fast-running streams. Due to the construction of canals, it has penetrated into the lower Kashkadarya and Zarafshan rivers. It is a rare fish, known at present by only a few findings. It is included in the Red Data Book of USSR, Turkmenistan, and Uzbebistan; and is listed as Critically Endangered in the IUCN Red List (A1aeD).

Amu Darya sturgeon (Pseudoscaphirhynchus kaufmanni) is an endemic of the Amu Darya River. Similar to P. hermanni, it was once mostly distributed in the river’s lowland section. This species attains a maximum length of 75 cm, and is also a typical inhabitant of wide, turbid, fast-running streams. Due to the construction of canals, it has also penetrated into the lower Kashkadarya and Zarafshan rivers. It is not as rare as P. hermanni, but it is also extremely threatened. It is included into the Red Data Book of USSR, Turkmenistan, and Uzbekistan; and is listed as Endangered in the IUCN Red List (A1acd).

Zeravshan dace (Leuciscus lehmanni) is a poorly known rheophilic dace. It is naturally present in the Zarafshan River, and only in the lower reaches of the Surkhob River in the Amu Darya system. This species became rare in most native habitats due to the regulation of rivers; however, it is known to have colonized some water reservoirs through canals.

Troglocobitis starostini is an endemic species and the only representative of cave species in subterranean water bodies of the former USSR. This species is blind, devoid of pigment, and its scales are not developed. It is known from only one locality – a subterranean lake in a sinkhole near the foot of a spur of the Kukgitang, east of the village of Karlyuk, Turkmenistan.

Other noteworthy fishes

Eastern crested loach (Nemacheilus longicaudus) is a poorly known loach that is commonly considered conspecific with Western crested loach (Paracobitis malapterura), although clearly morphologically different. It is widely distributed in the Amu Darya and Zarafshan systems, and also in streams of the northern slope of Kopetdag. It inhabits both slow and fast current waters, both turbid and clear. It is not clear from the literature which species occurs in Tedzhen (Har Rud) and Murghab; originally P. malapterura was described from Syria, and it was also reported from the Helmand River in Sistan. This group of Paracobitis species needs further study.

Bukhara roach (Rutilus rutilus bucharensis) is a subspecies that is clearly morphologically different from the geographically close R. rutilus aralensis, which, before the regulation of the Amu Darya, had never migrated above the delta. Rutilus rutilus bucharenis is distributed in plain sections and lakes of the main Amu Darya course and lower sections of its tributaries. At present, because of unregulated translocations of different forms of roach throughout Middle Asia, it is not clear where native populations of the Bukhara roach still occur.

Capoeta capoeta heratensis from the Tedzhen (Herirud) and Murgab rivers in Afghanistan and Turkmenistan, and Capoeta capoeta steindachneri from the upper Amu Darya, Zeravshan (from Pendzhikent down to lower reaches), Kafirnigan (from lower reaches to upstream), and upper Syr Darya (this needs confirmation) need special taxonomic studies with regard to the species complex, Capoeta capoeta, which is widely distributed from Kura to Amu.  

Triplophysa dorsalis kafirnigani is only known from the original description from the Kafirnigan River (upper Amu tributary).

Ecological phenomena

In the past the Amu Darya River played an important role in maintaining fish stocks of the Aral Sea. Its floodplains and delta, with its lakes, have created favorable conditions for the natural reproduction of the major economic fish such as bream, carp, and roach. In the Amu Darya River, the migratory Aral barbel (Luciobarbus brachycephalus) and Fringebarbel sturgeon (Acipenser nudiventris), which fed in the sea, migrated more than 1000 km into rivers for spawning.

The number of riverine fish species declined and the distribution of Amu Darya sturgeon (Pseudoscaphirhynchus kaufmanni) and pike asp (Aspiolucius esocinus) became narrower. Their lower distribution boundary is now 200 km and 600 km, respectively, further upstream than before. The Fringebarbel sturgeon (Acipenser nudiventris) and dwarf sturgeon (P. hermanni) completely disappeared from the river, but may still occur in the system in the Karakum Canal. It is thought that the main reason for their disappearance is the change in the water chemical composition. The migratory stocks of Aral barbel (L. brachycephalus) disappeared, but a strictly riverine stock exists in the upper part of the lowland course of the Amu Darya.

Justification for delineation

The ecoregion encompasses a large river drainage, Amu, with its historic tributaries, Tedzhen and Murghab (now interconnected by canals). The mountainous zones occupy a separate ecoregion, the Upper Amu Darya [631]. The border between the Middle Amu Darya and the Upper Amu Darya [631] is not sharp, but it is clear. The main criterion is the distribution of Pseudoscaphirhynchus species and other fishes preferring flatland sections, plain lakes, and channels with slow to moderately running water. The fauna of the ecoregion is different from the Lower and Middle Syr Darya ecosystem [626], which is similar to this ecoregion by the presence of two endemic species of Pseudoscaphirhynchus, one endemic species of Leuciscus, the presence of Capoeta (probably natively absent from Syr Darya), at least five species of Balitoridae, and some other features.

Level of taxonomic exploration

The level of taxonomic exploration is fair in general, although poor for some groups of species, especially balitorids.