Past, Present and Future of the Aral Sea -A Review of its Fauna and Flora before and during the Regression Crisis - PubMed (original) (raw)

Past, Present and Future of the Aral Sea -A Review of its Fauna and Flora before and during the Regression Crisis

Igor S Plotnikov et al. Zool Stud. 2023.

Abstract

We review the past, present and possible future of the Aral Sea system in context of the human caused regression crisis that resulted in the drying out of the larger part of this original brackish water sea. The results are put into the context of other threatened saline lakes and the general water crisis in the world due to overexploitation of water resources and climate change. We cover the geographic history and hydrology from the origin of the sea 17,000 years ago to the present. The original biota including animals, higher plants and algae are covered in full detail, and tracked through the regression crisis. We put special emphasis on fish and fisheries because of their economic importance for the surrounding populations. We also review the side effects of the regression in terms of human health and changes to the terrestrial environment and local climate. We explain the dramatic improvements to the fauna in the northern Small Aral Sea following the construction of dams to retain its waters and discuss future options to further improve this restored water basin. We contrast this with the progressing hypersalinization of the remnants of the southern Large Aral Sea, which faces conditions that will eventually render a "Dead Sea" condition hostile to all metazoan life. We end by highlighting the partial restoration of the Small Aral Sea as an example of how much restoration can be achieved for relatively little financial expense and in a short period, when good ideas, kind hearts and hard work operate together for the benefit of the environment and our human society.

Keywords: Agriculture; Ecology; Fisheries; Global Change; Irrigation; Saline lake.

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Figures

Fig. 1.

Fig. 1.

The position of the Aral Sea in Central Asia. The only water inflow is from the southern Amu Darya and the northern Syr Darya rivers, which originate in the Pamir and Tien Shan Mountains. The Aral Sea is depicted with its present, highly reduced extension. Modified from www.earthmaps. org and Plotnikov et al. (2021b).

Fig. 2.

Fig. 2.

The Aral Sea before the regression and now. Light blue shows the original sea; dark blue is the present extension. The variable shorelines of the hypersaline Large Aral is shown in yellow. The inset at upper left shows the existing Kokaral Dam and plans for an additional dam to restore even more of the Small Aral Sea. Based on Plotnikov et al. 2021b.

Fig. 3.

Fig. 3.

A and B, Geological history and topographic details of the Aral Sea from late Pliocene to present; the extensions of the present Black Sea, Caspian Sea and Aral Sea are shown in outline. The large Akchagyl Sea (or Basin) (~3.2–2 mln. years BP) covered a vast area and connected to the Black Sea by the Manych-Kerch Pillway. The later Apsheron Sea (~1.8–0.7 mln. years BP) was smaller, but still larger than the present Caspian Sea. C, The position of the present Aral Sea in its extension before the modern regression. D, Topographic and hydrological details of the Aral Sea as of about 1960. Original figure partially based on Krijgsman et al. (2019).

Fig. 4.

Fig. 4.

Aral Sea Fauna. Important native and introduced species in the Aral Sea fauna.Mesocyclops leuckarti and Arctodiaptomus salinus were important members of the zooplankton, but the latter was replaced by the introduced Calanipeda aquaedulcis. In the benthos_Dikerogammarus aralensis_ was displaced by the introduced shrimp_Palaemon elegans_. Bivalves of the genus Adacna,Cerastoderma and the introduced species Abra segmentum were important food for fish. The same is true for the introduced polychaete_Hediste diversicolor_. The fish depicted were all valuable commercial fisheries. Chironomid larvae and pupae were important food items for fish. The Aral Sea Trout and the Aral Sea Sturgeon have both gone extinct. Further details in text.

Fig. 5.

Fig. 5.

Highly schematized representation of reproductive patterns of native fishes in the Aral Sea. A–D summarises the migratory patterns explained in detail in the text. A, Long distance migration into the rivers for spawning. B, Shorter distance migration into rivers for spawning. C, Migration from open sea to shallow coastal waters for spawning. D, Fish that stay and reproduce near the shore.

Fig. 6.

Fig. 6.

Salinity and inflow of water for the Aral Sea. A, Total inflow to the Aral Sea during the regression and caused by diversion for irrigation purposes. B, The resulting increase in salinity; after 1990 the waters of the Large and Small Aral were separated and evolved independently of each other; the inserted maps show the decrease in area. After 2000 also the eastern and western parts of the Large Aral became separate water bodies, but both rapidly hypersalinizing. The construction of the dams that kept water in the Small Aral, had almost immediate effects. On the axis is indicated key events for the fauna in the system; further details in text. Modified and extended with new data from Plotnikov et al. (2021b).

Fig. 7.

Fig. 7.

Zooplankton recorded at fixed stations during the crisis. The percentages indicate the number of fixed sampling stations where the taxon was recorded. Native cladocerans, cyclopoids and calanoids all declined. The introduced calanoid_Calanipeda aquaedulcis_ initially spread throughout the sea. Detailed methodology explained in Plotnikov et al. (2021b).

Fig. 8.

Fig. 8.

Zoobenthos collected at fixed stations during the crisis. The percentages indicate the number of fixed sampling stations where the taxon was recorded. Detailed methodology explained in Plotnikov et al. (2021b).

Fig. 9.

Fig. 9.

The Aral Sea regression crisis. A, The desert left by the vanished sea is slowly being populated by drought and salt resistant plants. B, The first, primitive dam over the Berg Strait. C, Local fishermen look from the north at the final Kokaral Dam over the Berg Strait. D–E, ESA Spot satellite images of the Small Aral Sea soon after the dam construction and showing the increase in area already during the first year. F, Commercial fishing from small boats in the reconstituted Small Aral Sea.

Fig. 10.

Fig. 10.

A, Commercial fisheries yield for the Aral Sea system. For early years only intermittent data are available. The yield declined to virtually nil during the regression crisis after 1960, but then recovered in the partially restored Small Aral Sea. The inserted figure shows the decline in fish biodiversity. B, Yield per species of commercial fisheries in the restored Small Aral Sea. Data after 2012 are not completely available.

Fig. 11.

Fig. 11.

Total fish catch in the lower Amu Darya. In 1992 the landings had decreased to 13% of the amount in 1972. The blue part of columns is the ratio of introduced fishes in the total landings. Catches decreased due to the Aral Sea Crisis. (data from Pavlowskya 2022).

Fig. 12.

Fig. 12.

Causes and effects in the Aral Sea crisis. Hatched outlines show the extension of the sea after the regression had split it into two main bodies in the south and the Small Aral Sea in the north. (1) Diversion of water for irrigation resulted in (2) disastrously reduced inflow to the sea from ca.1960 onwards (3) Almost simultaneously planned species introductions seriously disturbed the native fauna (4) The reduced water inflow caused area regression, increased salinity and therefore serious reduction in biodiversity (5) Almost all fish disappeared with serious economic consequences for the human population (6) Sediment form the dried out sea bottom was blown into the air, causing very serious health problems for the human population (7) At the height of the area regression in 1990, the northern Small Aral Sea was connected to the vanishing Large Aral only through eastern Berg Strait, since the western Auzy-Kokaral Strait had dried out; a dam constructed in 2005 across the Berg Strait now retains inflowing water from the Syr Darya (8) Water level in the Small Aral Sea rapidly increased and salinity decreased; the fauna was reconstituted from refugial populations and fisheries recovered, where it again became an important commercial asset. (9) The larger part of the original Aral Sea continues to degrade into hypersaline water bodies and dried out salt flats with little or no metazoan life (10) The surrounding arid steppe now suffers from more extreme weather oscillations, since Aral waters no longer act as a buffer to temperature (11) In the future, climate caused, decreased precipitation at the sources of the two rivers will add to the shortage of water.

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References

    1. Agency of IFAS. 2022. Crisis of the Aral Sea. Agency of IFAS for implementation of the Aral Sea basin. Available at IFAS. Available at: https://aral.uz/en/crisis/. Accessed 7 Apr. 2022.
    1. Aladin NV. 1991. Thanatocenoses of separating bays and gulfs of the Aral Sea. Proc Zool Inst Acad of Sci USSR 237:60–63. (in Russian)
    1. Aladin NV, Kotov SV. 1989. The Aral Sea ecosystem original state and its changes under anthropogenic influences. Proc Zool Inst Acad Sci USSR 199:4–25. (in Russian)
    1. Aladin NV, Gontar VI, Zhakova LV, Plotnikov IS, Smurov AO, Rzymski P, Klimaszyk P. 2019. The zoocenosis of the Aral Sea: six decades of fast-paced change. Enviro Sci Pollut R 26:2228–2237. doi:10.1007/s11356-018-3807-z. - PMC - PubMed
    1. Aladin NV, Plotnikov IS. 1995. Changes in the Aral Sea level: paleolimnological and archaeological evidences. Trudy Zoologicheskogo Instituta 262(1):17–46. (in Russian)

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