Desiccation of the Aral Sea, the former 4th largest lake by area, is an unprecedented example of fast anthropogenically driven degradation of a large aquatic ecosystem. As a countermeasure preventing further desiccation, a 12-km long dam was constructed isolating the northern part of the Aral Sea from the rest. The “restarted” North Aral had been restored within several years from a “dying” ecosystem to a highly productive large lake. The effort led to stabilization of the North Aral volume, and was widely recognized as a success in large-scale lake restoration. As a side effect of restoration measures, part of the freshened waters overflowed into remaining semi-isolated lakes, causing them to become meromictic and creating extreme environments with strong vertical gradients of salinity, light and temperature. The deep layers of these lakes quickly developed to anaerobic environments dominated by methanogenic and sulfate-reducing microorganisms benefiting from a large amount of organic matter. By using outputs of field observations and modeling results we demonstrate the decisive role played by the mixing conditions in ecosystem adaptation to external drivers. While the North Aral Sea is restored to the well-mixed state similar to that before its desiccation started, its seasonal mixing regime is currently in unstable equilibrium, wobbling between polymictic and dimictic conditions. The fragility of this seasonal pattern is demonstrated by modeling results: slight changes of the water level or transparency may turn the Aral Sea to steadily dimictic or polymictic state.  

Primary Presenter: Georgiy Kirillin, Leibniz-Institute of Freshwater Ecology and Inland Fisheries (georgiy.kirillin@igb-berlin.de)

Authors:

Georgiy Kirillin, Leibniz-Institute of Freshwater Ecology and Inland Fisheries  (georgiy.kirillin@igb-berlin.de)

Hans-Peter Grossart, Leibniz Institute of Freshwater Ecology and Inland Fisheries  ()

Alexander Izhitskiy, Shirshov Institute of Oceanology, Russian Academy of Sciences  ()

Abilgazi Kurbaniyazov, International University of Tourism and Hospitality of Republic of Kazakhstan AND International Kazakh-Turkish University named after Khoja Akhmet Yassawi, Turkestan, Kazakhstan  ()

Tom Shatwell, Helmholtz Centre for Environmental Research - UFZ  ()

Sven Tobias-Hünefeldt, Leibniz Institute of Freshwater Ecology and Inland Fisheries  ()

Peter Zavialov, Shirshov Institute of Oceanology, Russian Academy of Sciences  ()