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The Aral Sea
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The Aral Sea
The Aral Sea, located in Central Asia in the lowlands of Turan, is historically a saline lake.
Administratively the water body is divided between Uzbekistan and Kazakstan (both countries were part of the former Soviet Union). It is in the center of a large, flat desert basin. The Aral Sea is a prime example of a dynamic environment. In 1960 it was the world's fourth largest lake, the size of the entirety of Southern California (26,250 square miles).
In the past few decades, the Aral Sea's volume has decreased by 75 %, the equivalent of draining Lakes Erie and Ontario, and its surface area by 50 percent. The shoreline has receded up to 120 km from its former shore. Sea level has fallen by more than 16 meters in this already shallow sea. This is a drastic change, but, in the far distant past, the Aral Sea has completely dried up. It has also been much larger than it was in 1960. The controversy about the Aral Sea Region arises because the change is human induced, maybe even on purpose, not the natural cycle of environmental change. During natural cycles, changes occur fairly slowly, over hundreds of years. Human induced environmental changes occur more rapidly.
The Aral Sea is a closed system; water flows in mainly from two rivers, the Syr Darya and Amu Darya, but water does no flow out of the Aral. The only natural water loss is via evaporation, and a great deal of water is lost by way of this process. The sources of the river water are glaciers high up in the Hindu Kush and Pamir Mountains to the southeast of the Aral Sea. The Amu Darya, historically known as the Oxus, begins in the Pamir Mountains in Ubekistan and travels 1578 miles to the Aral.
The Syr Darya, historically known as the Jaxartes, begins in the Tien Shan Mountain Range in Kazakstan and travels 1370 miles to the Aral. Because it is a closed system, the Aral Sea historically has a good indicator of global changes. Since the Pliocene Epoch (more than 2 million years), the Aral depression has been repeatedly flooded and desiccated (dried up). During cooling/glacial periods, the Aral Sea decreased in size because water was tied up in glaciers. During periods of global warming (inter-glacial periods), glaciers melted, and the volume of the Aral Sea increased. The Aral Sea has always been in a state of flux because of its sensitivity to natural changes in the global environment.
The current condition of the Aral Sea is a human created situation that is not necessarily any worse than the natural cycle has produced in past years. However, the existing change is in the opposite direction of what nature would dictate. Presently world wide, glaciers are regressing and global sea level is on the rise. It's controversial whether this is part of a natural cycle (currently in an interglacial period) or caused by human induced global warming (increased carbon dioxide in the atmosphere). The Aral Sea should be getting fuller, but it isn't. The volume of the nearby Caspian Sea is increasing, which also causes a host of problems.
The Aral sea disaster
The two rivers Amu-Dar'ja and Syr-Dar'ja are heavily used for irrigation by the republics of Uzbekistan and Kazakstan. Especially in the last 35 years irrigation has been greatly intensified. Since this period the desiccation of the Aral Sea has been dramatic, with the result that the former fourth-largest lake of the world is now the world's eighth largest lake. One of the large irrigation areas is the Amu-Dar'ja delta in the south of the Aral sea. The irrigated area extends over approximately 28000 sq km, and is mainly used for the cash crops cotton and rice. The water demand for agricultural use increased of course in the same time and the discharge to the Aral sea by the two rivers dropped to almost null.
Along the former shoreline salt has accumulated due to evaporation and solonchaks have developed. As a result of the strong NE winds in this area, the salt is picked up and transported by aeolic processes and through deflation lands on the irrigated fields in the south. In addition the north of the Amu-Dar'ja delta used to be an important ecosystem with a large variety of flora and fauna. The increasing salinity and the water shortage have led to a vast degradation of these areas. In addition the productivity of the agricultural fields dropped significantly due to secondary salinization as a result of capillary uprising of soil water.
The related soil degradation is fought by the local people by "soil flushing" several times a year. The highly loaded water is carried to so-called "collectors" from which the water evaporates completely unused.
In addition there are high water losses due to the old irrigation network. About 80% of all irrigation channels lack any kind of base sealing, which results in high water losses by evaporation and infiltration.
The sum of these factors has resulted in the continuous desiccation of the Aral Sea since 1960. The consequences of this process are dramatic and the most important are summarized below.
- Mesoclimatic changes (increase of continentality)
- Increase of salt and dust storms
- Shortening of the vegetation period
Ecological / economic consequences
- Degeneration of the delta ecosystems
- Total collapse of the fishing industry (originally 44,000 t/a)
- Decrease of productivity of agricultural fields
- Increase of serious diseases (e.g. cholera, typhus, gastritis, blood cancer)
- Increase of respiratory system diseases (asthma, bronchitis)
- Birth defects and high infant mortality