Aral Sea, Kazakhstan

The Aral Sea is an endorheic lake lying between Kazakhstan in the north and Uzbekistan in the south. The name roughly translates as "Sea of Islands", referring to over 1,100 islands that had once dotted its waters; in the Turkic languages aral means "island, archipelago". The Aral Sea drainage basin encompasses Uzbekistan and parts of Tajikistan, Turkmenistan, Kyrgyzstan, Kazakhstan, Afghanistan and Iran.

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Derelict ships in the former port in Moynaq, Uzbekistan (Credit: Taylor Weidman)

Until the early 1960s, the lake surface level was stable at about 53.5 m above sea level. At the time, the lake was the fourth largest on Earth, with the volume about 1070 km2 and the area over 65000 km2. Since the 1960s after the rivers that fed it were diverted by Soviet irrigation projects the Aral Sea has been shrinking due to unsustainable irrigation and diversions of water from the lake’s tributary rivers, Amudarya and Syrdarya. Today, the total water level drop is about 24 m, and the remaining area of the water body of the current Aral Sea amounts to only about 10% of its original volume. By 1997, the Sea had declined to 10% of its original size, splitting into four lakes: the North Aral Sea, the eastern and western basins of the once far larger South Aral Sea, and one smaller intermediate lake. By 2009, the southeastern lake had disappeared and the southwestern lake had retreated to a thin strip at the western edge of the former southern sea; in subsequent years, occasional water flows have led to the southeastern lake sometimes being replenished to a small degree.

By the late 1990s, the salinity of the once brackish lake increased by an order of magnitude and exceeded 100‰. Today, the residual lake consists of two separate parts, referred to as the Small Aral Sea and the Large Aral Sea. The former makes up the northernmost part of the original Sea and separated from the main body of the lake in 1989. The Large Aral Sea in itself has almost split into two parts, namely, the shallow to ephemeral (>3 m deep) but broad eastern basin and the smaller but relatively deep western basin (nowadays ~39 m). In summer, the eastern basin acts as a colossal evaporation pond; therefore, the salinity of the eastern basin is, generally, much higher than that of the western lobe. The two basins exchange water and properties through a narrow(≈1 km) but rather deep (≈5 m) connecting channel.

As the salinity of the Sea increased, the first evaporatively precipitated compound was the calcium carbonate. At somewhat higher salinities, magnesium carbonate MgCO3 was also precipitated. The subsequent salinisation led to precipitation of gypsum, which started in the late 1980s when lake salinities exceeded 26–28 g/kg.

Massive deposits of gypsum precipitated during the recent and ancient regressions of the Sea can be seen on and beneath the former lake bottom. Processes expected at even higher salinities than today, include the widespread precipitation of mirabilite Na2SO4.10H2O, halite NaCl, glauberite CaSO4.Na2SO4, and epsomite MgSO4.7H2O.

In an ongoing effort in Kazakhstan to save and replenish the North Aral Sea (“Small Sea”), the Dike Kokaral project was completed in 2005. Dike Kokaral is a dam across a narrow stretch of the Aral Sea, splitting off the North Aral Sea ("The Small Sea") from the much larger South Aral Sea ("The Large Sea”). By 2008, the water level in the North Aral Sea had risen by 12 m (compared to 2003). Salinity has dropped, and fish are again found in sufficient numbers for some fishing to be viable. Today the maximum depth of the North Aral Sea is more than 40 metres.

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The desiccated basin of the “Large Aral Sea” with improved water retention in the North Aral Sea (Small sea”).

Before desiccation onset in 1960, the autumn/winter deep convection was typically responsible for complete mixing and ventilation of the water column. Therefore, the entire column contained oxygen at high concentrations. No hydrogen sulphide content was ever reported for the pre-desiccation period, except sporadic and unconfirmed occurrences in limited deltaic areas with enhanced buoyancy-controlled stratification, although traces of H2S in Aral bottom sediments have been long known. This situation persisted through the initial stage of the desiccation in 1961–1991, but significantly changed between 1991 and 2002. By the early 2000s, enhanced density stratification had arisen, largely impeding vertical mixing and ventilation in the water bodies. As a consequence, the bottom portion of the water column turned anoxic and contained hydrogen sulphide.

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Shrinking of the Aral Sea between 1989 and 2014

Ongoing desiccation of the Aral Sea dramatically increased the number of dust and salt storms in the area. Satellite images show that there are up to ten major dust storms occurring annually in the region, with most of them occurring between April and July. Before the desiccation of the Aral Sea, evaporation pressure from the water surface dampened the strength of the northerly and north-easterly winds. Desiccation means the protective action of the suprasea humidity is significantly reduced. As well the drying of the sea has left behind a large amount of salt, and capillary evaporation further increases the amount of salt atop the now exposed sea bed. Strong north-easterly winds now pick up sand, salt, and clay, so creating saltier dust storms. The salt content in the dust in the summer can be 30–40% by volume and was as high as 90% in the winter. Agricultural areas downwind are suffering from increased salinisation problems.

Large bodies of water, like the Aral Sea, can moderate a region's climate by altering moisture and energy balance. Loss of water in the Aral Sea has changed surface temperatures and wind patterns. This has resulted in hotter summers and cooler winters (an estimated 2˚C-6˚C change in either direction) and the emergence of dust storms over the area.

The Aral Sea is today considered an example of ecosystem collapse due to upstream irrigation and water diversion. There are similar, but not as acute problems in many other arid riverine systems with irrigation canals worldwide. The Jordan River in the Middle East and the Murray River drainage basin in Australia are two other examples where over-extraction upstream creates downstream problems. In Australia, as in the feeder region to the Aral Sea, the upstream irrigation, especially of cotton, creates many difficulties for downstream dwellers, 

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Dust storm in April, 2008

As part of the irrigation plan, pesticides were increasingly used starting in the 1960s to increase cotton yields, which further polluted the Aral water with toxins such as DDT. Furthermore, "PCB-compounds and heavy metals" from industrial pollution contaminated both water and soil. Due toendorheic drainage and the minimal amount of water remining in the Aral sea, concentrations of these pollutants have increased drastically in both the water and soil. These substances form wind-borne toxic dust that spreads throughout the region. People living near the Aral Sea come in contact with pollutants through drinking water and inhalation of contaminated dust. Furthermore, due to the presence in drinking water, the toxins have entered the food chain. As a result, the land around the Aral Sea is heavily polluted, and the people living in the area are suffering from a lack of freshwater and health problems, including high rates of certain forms of cancer and lung diseases. Respiratory illnesses, including tuberculosis (most of which is drug-resistant) and cancer, digestive disorders, anaemia, and infectious diseases are common ailments in the region. Liver, kidney, and eye problems can also be attributed to the toxic dust storms. All of this has resulted in an unusually high fatality rate among vulnerable parts of the population: the child mortality rate is 75 in every 1,000 newborns, and maternity death is 12 in every 1,000 women. The dust storms also contribute to water shortages through salinisation. The overuse of pesticides on crops to preserve yields has made situation this worse, with pesticide use far beyond health limits. Crops in the region are destroyed by eolian-aided salinisation, and fields are being flushed with water at least four times per day to try to remove the salinity from the soils. The land is decaying, causing few crops to grow besides fodder, which is what the farmers in Kazakhstan are now deciding to seed.

In an ongoing effort by Kazakhstan to save and replenish the North Aral Sea, the Dike Kokaral dam project was completed in 2005; in 2008, the water level in this lake had risen by 12 m (39 ft) compared to 2003. Salinity in the north arm has dropped, and fish are again found in sufficient numbers for some small fishing ventures are beginning to be viable once more. Yet, the Aral Sea fishing industry in its heyday (pre-1960s) employed some 40,000 and reportedly produced one-sixth of the Soviet Union's entire fish catch. In the 1980s commercial harvests were becoming unsustainable, and by 1987 commercial harvesting became nonexistent. Due to the declining lake levels, salinity levels had become too high for the 20 native fish species to survive. The only fish that could withstand the high-salinity levels was flounder. Due to the declining sea levels, former fishing towns along the original shores have become ship graveyards. Aral, formerly the main fishing port, is now several miles from the sea and has seen its population decline dramatically since the beginning of the crisis. The town of Moynaq in Uzbekistan had a thriving harbour and fishing industry that employed about 30,000 people; it too now it lies miles from the shore. Fishing boats lie scattered on dry land, land that was once covered by water.

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