Modern condition and analysis of anthropogenous-climatic transformation of vegetation of lakes of the northern Steppe land

Abstract

In this article, the current and former distribution of higher aquatic vegetation has been analyzed for floodplain lakes, arenas lakes and third terraces lakes in the valleys of large and medium North-Steppe Dnieper rivers. The article is devoted to the current state analysis of the higher aquatic vegetation at North-Steppe Dnieper lakes, its dynamics over a long-term period, as well as the determination of the nature and extent of anthropogenic-climatic changes in vegetation. Anthropogenic influence is a major threat to the development and functioning of most aquatic ecosystems. Since the twentieth century, it has been intensified by trends to long-term climate changes, which are also largely result of human activity. Increasing temperature of the winter season does not contribute to snow accumulation. Reduction of snow accumulation (frequent thaws during the winter), regulation of river flow (formation of a reservoirs cascade and ponds) and accumulation of melt water in artificial reservoirs led to the smoothing of the peak of the spring flood. Thus, the factor that provided spring washing of floodplain lakes, limited their overgrowing by air-water vegetation and their waterlogging disappeared. The anthropogenic factors that influence negatively include: intensification of agriculture, plowing of coastal areas, unreasonable land reclamation, overgrazing, development of transport and engineering infrastructure, urbanization, recreation, and chemical pollution. The presented data was obtained on the basis of processing our own research materials of 2009–2018 and literary and archival materials analysis (the herbarium of the Dnipropetrovs’k National University and the archive of the Research Institute of Biology). Natural Northern Steppe Dnieper lakes are located mainly in river valleys, so the study area was conventionally divided into sections: the large river valley (Dnieper) and the middle rivers valleys (Samara and Orel). Three ecological groups of macrophytes were reviewed and compared: hydatofites (submerged species), pleistophytes (species with floating leaves) and helophytes (air-water species). The vegetation of Dnieper floodplain lakes practically did not change for all three formation groups. The number of immersed plants communities within the floodplains of medium-sized rivers has decreased by three. The pleistophytes and helophytes associations decreased to fragments of associations. The lakes vegetation within the sandy Dnieper terrace practically did not change for all three formation groups. The submerged lakes plants associations within the sandy medium-sized rivers terraces have been reduced by two. As part of the lakes vegetation on the Dnipro saline terraces, fragments of associations of the two species are considered extinct. A new association of southern adventive species Ruppia maritima L. has appeared within the limits of the middle rivers saline terrace. Changes in higher aquatic vegetation are characteristic of all types of lakes. Changes occur in the direction of crowding out higher aquatic vegetation communities by airborne plant communities. The consequence of the anthropogenic-climatic transformation of aquatic ecosystems is increased mineralization, siltation, and, as a result, intensive overgrowing of lakes by aboriginal and adventive species with a wide ecological amplitude (replacement of sensitive to environmental changes species).