ИСТИНА

Volga-Akhtuba floodplain is the part of the Lower Volga region. The territory of the Volga-Akhtuba floodplain(VAF) is an unique arid wetland, where the dynamics of ecosystems are largely determined by the hydrological regime of the Lower Volga, which is regulated by the Volzhskaya hydroelectric power plant dam – Europe’s largest HPP. The extreme drought in the VAF occurred in the 2015, arised from the lowest water flow and water level during the spring-summer flood for the entire period of hydrological observations. This drought of 2015 resulted in the lowest flooded areas for the entire period of satellite observations, and thus the ecological catastrophe in the whole VAF territory. A dynamics of VAF key ecosystem components - plant cover and water bodies - was examined. Their recovery after the disastrous water deficit in 2015 was assessed on the basis of the joint analysis of multispectral satellite data and ground observations on VAF water bodies, and geobotanical descriptions. A special attention was paid to the 14 test sites where the authors conduct the long-term monitoring of the local ecosystem dynamics by the remotely sensed data. For these test sites the data on the extremely dry 2015, and relatively wet 2016-2018, was assessed and compared with the data for the preceding period of low water 2006-2014. The water bodies, and plant community dynamics in the VAF were examined on the basis of water and vegetation index value dynamics. After the extreme drought in 2015, the VAF ecosystems in general, has undergone the significant changes, when compared to the preceding low-water period 2006-2014. The disappearance, drastic shallowing and overgrowth by hygrophytes observed in the significant number of the permanent water bodies all over the floodplain has reduced the stability of VAF wetland ecosystems. Currently, even a slight water deficit may lead to the progress of desertification, and VAF contamination with weeds, the loss of inland VAF water bodies and its ecosystems (water body silting and thus, withering of VAF parts), as well as the loss or the substantial transformation of native wetland phytocenoses. Similar processes have been observed in other arid wetlands like floodplain and Delta of the Ural river (Kazakhstan), and Gavkhuni wetlands (Iran).