# Long-Term Dynamics of Persistent Organic Pollutants in Water Bodies of the Aral Sea-Syrdarya Basin
### Causes of the Ecological Crisis and Its Consequences  
The Aral Sea is one of the largest inland water reservoirs. It is located in the desert zone of Central Asia, within the Turan Depression at the eastern edge of the Ust-Urt Plateau. The average annual lake level from 1911 to 1960 was 53 m above sea level (a.s.l.) of the Baltic System (BS) according to the data of instrumental observations. At this level, the lake area of the Aral Sea was about 68.3 thousand km\({}^{2}\); the water volume was 1064 thousand km\({}^{3}\) and the average depth was 16.1 m. The lake contained 11,000 islands, which gave the lake its name: \"Aral\" means \"island\" in the Kazakh language [6,7]. Another description of the term \"Aral\" or \"island\" is a translation from the Turkish language, which, in this case, means \"a water island, surrounded by deserts\". Based on the morphological structure of the Aral Sea basin, after the lake level had dropped dramatically, today, the Aral Sea is separated into two water bodies: a relatively isolated smaller northeastern part, namely, the Small Aral Sea, which has an area of 6000 km\({}^{2}\) at the level of 53 m a.s.l., with a water volume around 80 km\({}^{3}\) (9.1 and 7.5% of the lake's former total area and volume, respectively), and the Large Aral Sea [8,9]. The lake's water and salt balances, hydrological and hydrochemical regime, biological productivity, and the existence of the Aral Sea itself as a geographic entity are determined by the tributaries of the two large Central Asian rivers: Amudarya and Syrdarya, and their catchments. The former total average annual runoff from these river basins was estimated at 112 km\({}^{3}\) (75 km\({}^{3}\) and 37 km\({}^{3}\) for Amudarya and Syrdarya, respectively). Figure 1: Hydrographic network of the (Small) Aral Sea–Syrdarya Basin on the territory of Kazakhstan (own draft). In the early 1960s, the Soviet Union decided to expand irrigation on a new scale in Central Asia and Kazakhstan in order to increase the production of cotton, food, employment, etc. According to [PERSON]. [10], the area of irrigated land in the Aral Sea region was 9,354,000 hectares in 1987, i.e., it increased by 1.7 times compared with 1950 (5,421,000 hectares). Since the beginning of 1960, the area of irrigated land in the Syrdarya River basin has increased from 1,200,000 to 3,260,000 hectares, including the lower reaches of the river from 88,000 to 350,000 hectares [11]. The expansion of irrigated land area was accompanied by an increase in water use. In 1980, the total water consumption in the Aral Sea basin reached 120,690 million m\({}^{3}\), and water withdrawal for irrigation purposes reached 106,790 million m\({}^{3}\) compared with 60,160 and 56,152 million m\({}^{3}\) in 1960, respectively. In particular, the volume of total water consumption from the Syrdarya River increased by 1.8 times during this period, and water withdrawals for irrigation purposes by 1.7 times, i.e., it reached 46,445 million m\({}^{3}\) versus 27,602 million m\({}^{3}\) in 1960 [12]. The water withdrawal from the Syrdarya River increased during the years of huge irrigation project development from 32 to 55 km\({}^{3}\) per year and in the lower reaches from 3.3 to 6.0 km\({}^{3}\). This meant the water withdrawal exceeded 1.4 times the available water resources in this region due to the reuse of returned water [11]. More than 1500 irrigation canals, about 40 large- and medium-sized reservoirs, and more than 300 collectors with a total length of 83,000 km were built in the Syrdarya River basin. The length of the irrigation network in the basin exceeded 120,000 km [11; 12]. Since 1961, as a result of the abovementioned circumstances, the river runoff to the Aral Sea has declined intensively, accompanied by a rapid drop in the lake level. During 1961-1970, the intensity of the lake level decline was about 0.21 m/year. In 1981-1986, there was no river discharge in some years, and the lake level decline was 0.89-1.09 m/year during some years [13].