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Ecoregion Description


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629: Aral Sea Drainages

Major Habitat Type:

large lakes

Author:

Nina Bogutskaya, Zoological Institute, Russian Academy of Sciences, Russia

Countries:

Kazakhstan; Turkmenistan; Uzbekistan

Boundaries:

The Aral Sea Drainages ecoregion lies in the countries of Kazakhstan, Uzbekistan, and Turkmenistan. The ecoregion comprises the remnants of the former Aral Sea, including the Large Aral (or so-called Bol’shoy Aral in the southern part of the former sea where the Amu Darya River flowed), and adjacent deserted land. It excludes the Small Aral (Maly Aral) that belongs to the Lower and Middle Sry Darya [629] ecoregion.

The ecoregion’s western boundary is shared with the Turan Plain [450] along the spurs of the Ust-Urt [Ustyurt] Plateau and Assake-Audan Depression. The Sarakamysh [Sariqamish Kuli = Sarygamysh Koli] Depression (now a lake) is included in the ecoregion. The southern boundary crosses the former delta of Amu Darya south of Urgench and extends eastward to the Mynbulak Depression. Then it rounds the Bukantau Mountains and is contiguous with the Lower and Middle Syr Darya [626] ecoregion along the entire lower course of the Syr Darya River. This ecoregion also includes the waterless area between the lower Syr Darya and the Irgiz-Turgay area [601] - Peski Priaral’skiy Karakumy [Aral Mangy Qaraqumy], Peski Malyye Barsuki Desert, and Peski Bol’shiye Barsuki Desert [Ulken Borsyq Qumi]. The border shared with the Volga-Ural [410] ecoregion runs along the Chagray [Shaghyray Ustirti] Plateau.

Drainages flowing into:

Caspian Sea (West Asian endorheic basin)

Main rivers or other water bodies:

The main water bodies in the ecoregion include the Large Aral, Lake Sarakamysh [Sariqamish Kuli = Sarygamysh Koli], and irrigational canals of the lower Amu Darya River.

The Aral Sea is not deep. In the middle its depth is only 20-25 m, and only along the western coast does it reach 30 m (the maximum depth is 68 m). The sea level has been subject to considerable changes. The fluctuations mainly depend on water inflow from the Syr Darya and Amu Darya rivers since the average annual evaporation, some 920 mm, shows little variation. The water level is also influenced by strong winds, especially from the north. These winds in the spring and autumn can raise the water level up to 2-3 m between the mouths of the Syr and Amu, causing coastal flooding for many kilometers. There are also daily changes due to seiches.

Over the past few decades the Aral Sea has rapidly and steadily shrunk as countries in the Aral Sea basin have increasingly taken inflow from the Syr Darya and Amu Darya for irrigation expansion. In 1989 desiccation caused the Aral Sea to split into two parts: the Small Aral in the north and the Large Aral in the south. The difference in the hydrological regimes of the two new lakes has led to stabilization of the sea level and salinity in the Small Aral, whereas the Large Aral Sea has continued to dry up and salinize.

After the division in 1989, the Small Aral stabilized at 40 m asl and began to slowly rise due to a positive water balance. In contrast, the Large Aral sea level continued to decline due to a negative water balance, and salinity rapidly increased. It was quickly transformed from a mesohaline to a hyperhaline water body. In autumn 2002 salinity exceeded 70 g/l. The rapid decline of the Large Aral level actually destroyed large parts of the lower delta of the Amu Darya. Unlike the delta of Syr Darya where natural rehabilitation processes began after a dam along the Berg Strait was built, rapid degradation of Amu Darya delta continues (the delta does not actually exist – the water of Amu does not reach the former coast of the sea by the distance of several hundred kilometers). Restoration and rehabilitation of the Large Aral is practically impossible, as it would require large amounts of both the Syr Darya and Amu Darya waters that are diverted for irrigation. Syr Darya inflows to the Aral Sea have been greatly reduced, and almost nothing remains of Amu Darya inflows because all countries in the upper basin continue to divert almost all of it for irrigation. Most of the water from the irrigational canals of the lower reaches of the Amu Darya flows into some terminal reservoirs, both artificial and natural. One of the natural reservoirs is Sarakamysh Depression, which is now a lake.

Topography:

The Aral Sea (63,915 km2) comprises lakes of tectonic origin, and includes many islands. The largest of these are Kug-Aral, Vozrozhdemiya,  Barsa-Kel’mes, and Takmak-Ata. The northern coast of the sea is indented by large bays. The western coast is straight with steep spurs up to 190 m high. The eastern coast is sandy and low, indented by numerous narrow bays, bights, and inlets. The southern coast is formed by the Amu Darya delta, a low alluvial plain with numerous intermittent lakes, channels, and anabranches.

Climate:

The climate of this ecoregion is primarily temperate desert (BWk), but grades to temperate steppe (BSk) in the north. Mean annual precipitation ranges from 125 mm in the south to 240 mm in the north. In the extreme southern part of the ecoregion the average annual temperature is approximately 16º C. Winters are mild, with the temperate in January averaging –1 to 5 °C. Seasonal temperatures toward the northern part of the ecoregion vary widely, with hot summers and long, cold winters. Here, average January temperatures range between –13 to –16 °C.

Freshwater habitats:

Before anthropogenic desiccation and salinization, the Aral Sea was brackish, with average salinity between 8-10 g/l. It was a large shallow lake that was rich in silt and organic matter, and had a relatively high water temperature. It was also heavily vegetated along most coasts; for example, widespread and well-developed wetlands once occurred along the southern and southeastern coast connecting the deltaic areas of Syr and Amu.

Today, fresh or brackish water habitats have almost completely disappeared. Lake Sarakamysh, which now receives water from the lower Amu Darya, may be considered as a slight substitution of the sea. It, however, is heavily polluted by agriculture wastes, and fishes may contain dangerous amounts of pollutants in their tissues.

Terrestrial Habitats:

This ecoregion crosses the Central Asian northern and southern deserts, as well as Kazakh semi-desert. The southern desert is distinguished from the northern desert by a greater diversity of ephemeroids (e.g. Eremurus spp. and Rheum spp.) and ephemers (e.g. Bromus spp. and Malcolmia spp.). The Kazakh semi-desert in the northern part of the ecoregion is dominated by bunch grasses such as kovylok (Stipa lessingiana), tyrsik (Stipa sareptana), and tipchak (Festuca valesiaca).

Along the floodplain of the Amu Darya lies the Central Asian riparian woodlands. These woodlands, locally known as tugai, represent critical habitat for many migratory wildlife. Vegetation in this area is comprised of poplars (Populus diversifolia, P. pruinosa), dzhidda (Elaeagnus oxycarpa), willows (Salix spp.), and tamarix (Tamarix spp.). The herbaceous vegetation includes steppe, desert, and swamp species.

Fish Fauna:

The fish fauna of the lake historically has had poor diversity, with little more than twenty species in six families, most of which are cyprinids. This reflects the complex geological history of the Aral Sea (actually a terminal lake) that underwent a number of contractions and expansions. The whole fauna of the Aral Sea was of freshwater origin. However, most species were abundant and all of them were migratory (travelling up rivers far upstream for spawning) or semi-migratory (entering the deltas and lower reaches of Syr and Amu for spawning). Some examples of these include Fringebarbel sturgeon (Acipenser nudiventris), common bream (Abramis brama), Danube bleak (Alburnus chalcoides), common carp (Cyprinus carpio), ide (Leuciscus idus), roach (Rutilus rutilus), ziege (Pelecus cultratus), southern ninespine stickleback (Pungitius platygaster), and pike-perch (Sander lucioperca).

In the last several decades the fish fauna has experienced a change in composition.The first crisis in 1957-1960 was associated with planned and accidental introductions into the Aral Sea ecosystem. Over twenty fish species were introduced and most of them became established. However, all but the flounder, Plathichtys flesus, have been extirpated by now. The second crisis transpired in 1971-1976 when salinity of the Aral increased above 12-14 g/l and brackish water species of freshwater origin disappeared. The third crisis took place in 1986-1989 when salinity exceeded 23-25 g/l. By this time all brackish water species became extinct/ extirpated. When the lake divided into two parts in 1989, only seven species of fish (non-indigenous), ten common zooplankton species, and eleven common benthos species remained. In the Small Aral Sea, now only Platichthys flesus occurs.

In Lake Sarakamysh, in addition to a high number of introduced species, some abundant native species includes roach (Rutilus rutilus), common bream (Abramis brama), and Prussian carp (Carassius "gibelio").

Description of endemic fishes:

There are no endemic species in the Aral Sea.

Other noteworthy fishes:

The Aral Sea basin once supported a large number of forms/subspecies endemic to the basin (including the Syr and Amu drainages). These are Luciobarbus capito conocephalus, Luciobarbus brachycephalus brachycephalus, Alburnus chalcoides aralensis, Aspius aspius iblioides, Rutilus rutilus aralensis, and Salmo trutta aralensis. Some of these forms survived in a few riverine sections of Syr and/or Amu, or developed populations in recently constructed reservoirs.

The Aral migratory trout (Salmo trutta aralensis) was an exciting example of brown trout in the southeastern part of the ecoregion. However, it is most likely extinct since there have been no records for the last 50 years.

The Aral population of Acipenser nudiventris, the famous Fringebarbel sturgeon, was once abundant in the Aral Sea basin, migrating up the Syr and Amu rivers up to 2600 km for spawning. It almost disappeared by the end of 1960s, and there have been no records in Kazakhstan for the last 25-30 years. It was later stocked and introduced in some upper sections of the Syr, Amu, and Chu rivers, but is still rare.

The Aral barbel (Barbus brachycephalus brachycephalus) had once been the second (after the Fringebarbel sturgeon) most valuable commercial fish of the Aral Sea. It attained the length of 1 m and weighed over 20 kg. It was a migratory fish that travelled far upstream for wintering and spawning. The mass migration took place in July and coincided with the maximal water level in the Syr and Amu rivers. Dam construction, and later salinization, contributed to its decline. However, it survived in the middle and upper sections of the Amu Darya and Zeravshan rivers.

Other noteworthy aquatic biotic elements:

Historically, the ecosystems of the Aral Sea were exclusively productive, although taxonomic diversity was not high in both plankton and zoobenthos.

Ecological phenomena:

The Aral Sea was historically a unique example of a large, closed lake with brackish water. It was populated by primary freshwater fauna adapted to brackish water conditions, but able to spawn in freshwater.

Evolutionary phenomena:

Although the Aral Sea fish assemblage was historically young, it shed some light on the formation of the Central Asian fish fauna and its links with both the Caspian Sea (Ponto-Caspian) fauna and the Tertiary Siberian fauna.

Justification for delineation:

The ecoregion is delimited according to the former borders of the Aral Sea basin. However, the Syr Darya delta and connected lakes, as well as the Small Aral Sea, belong to the Lower and Middle Syr Darya ecoregion [629] because of the recent transformations of the Aral Sea hydrographical and hydrobiological characteristics. Historically, the Aral Sea basin is defined as a unique large, closed, and brackish lake that originated as a depression filled with river waters. It supported a poor, but unique assemblage of migratory and semi-migratory fishes adapted to forage and winter in the "marine" conditions of the lake.

Level of taxonomic exploration:

Good

References/sources:

Aladin, N. V., Filippov, A. A., et al. (2001)"Modern ecological state of the Small Aral Sea. Ecological Research and monitoring of the Aral Sea Deltas. A basis for restoration. Book 2" In 1997-1999 Final Scientific Reports. (pp. 73-82) UNESCO Aral Sea Project.

Aladin, N. V., Plotnikov, I. S., et al. (1995). "The Aral Sea desiccation and possible ways of rehabilitating and conserving its Northern part" Int. J. Environmetrics 6 17-29.

Aladin, N. V.,Kotov, S. V. (1989). "Natural condition of the Aral Sea ecosystem and the effect of manmade pollution" Proc. of Zool. Inst. Of Acad of Sci USSR 199 110-114.

Aladin, N. V.,Potts, W. T. W. (1992). "Changes in the Aral Sea ecosystem during the period 1960-1990" Hydrobiologia 237 67-79.

Karpevich, A. F. (1960). "Basing of aquatic organisms acclimatization in the Aral Sea" Trudy VNIRO 43(1) 76-115.

Nikol'skiy, G. V. (1940). "Fishes of the Aral Sea" Moscow: MOIP.

Williams, W. D.,Aladin, N. V. (1991). "The Aral Sea: recent limnological changes and their conservation significance" Aquatic Conservation: Marine and Freshwater Ecosystems 1 3-23.

World Wildlife, Fund (2001). "Terrestrial Ecoregions of the World" 2005 (2005; www.worldwildlife.org/science/ecoregions/biomes.cfm).

Yablonskaya, E. A.,Lukonina, N. K. (1962). "On the question of productivity of the Aral Sea" Okeanologiya 2(2) 298-304.

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