The head of the project: Evgeny A. Konstantinov
The title of the project: Reconstruction of the history of the largest lakes in the center of the East European Plain over the last 20 thousand years: the basis for forecasting changes in the lakes ecosystems in the 21st century
Key words: Lake Nero, Plescheevo Lake, Late Pleistocene, Holocene, history of lakes development, reconstruction of lake-level fluctuations, paleoclimate, forecast of dangerous natural processes
Summary
In the framework of the project it is planned to undertake a comprehensive study of the bottom sediments and lake terraces of Lake Pleshcheevo and Lake Nero with a goal of creating a detailed reconstruction of the water level fluctuations in the Late Pleistocene and the Holocene. Studying paleohydrology of these lakes, whose sediments represent the most complete sedimentary archives of the Late Pleistocene and the Holocene for the central part of EEP, has both fundamental and practical importance. The fundamental due to the fact that the powerful (up to 120 m) layers of sediments accumulated in the basins of these lakes represent the most complete sedimentary archives of the late Pleistocene and Holocene of the central part of EEP. However, the study of these paleoarchives does not correspond to the modern methodical level. This fact significantly reduces the density of the coverage area of Eastern Europe highly paleogeographic reconstruction for the Late Pleistocene (Database content NOAA), which in turn negatively affects the quality of the global paleoclimate constructions. The bulk of the publications devoted to the reconstruction of the history of lakes Plescheevo and Nero, refers to 50-90 years of XX century. This determines their overall methodological level, does not meet modern standards with extensive use of absolute dating methods and a detailed analysis of real deposits (Cohen, 2003; Bradley, 2013; Jones, Jordan, 2013). Over the past 30 years, systematic research has not been carried out on the problem, and single studies (Alexandrovsky, 2011; Wohlfarth et al., 2006; Lavrushin, 2016), which solved particular problems, do not allow the construction of a complete paleohydrological reconstruction. For these reasons, accumulated contradictions regarding the views of the transformation of the hydrological network of the territory of the Yaroslavl sector of the Volga basin region. Particularly, still unresolved are the questions regarding the levels of the studied lakes during the stage of the degradation of the Late Weichselian glaciation, and the validity of the ideas concerning the connection of lakes Nero and Pleshcheevo with the system of glacial water bodies (Gunova, 1975; Kvasov, 1975). Likewise debatable is the age of the lacustrine terraces that are well-defined along shore (Gunova, 1975; Quaternary formations map, 1968; Pisareva et al., 1998). Also there are significant disparities concerning the history of the fluctuations of the level of the lakes in the Holocene (Aleshinskaya, Gunova, 1997; Aleksandrovsky, 2011; Wohlfarth et al., 2006; Lavrushin, 2016).
The root of the practical value of the project is in the necessity of forecasting of the progressing dangerous exogenous processes and dangerous hydrological phenomena on the lake shores in the conditions of the expected climate changes (IPCC, 2013). The importance of such prediction is associated with the problem of ensuring the preservation of the objects of historical and cultural heritage located in the near-shore zone of lakes – in the ancient cities of Rostov and Pereslavl Zalesskiy. For example, the threat of a significant rise of the level of the lakes is quite realistic. For example, it has demonstrated by Lavrusin (2016) that the level of Lake Nero could exceed the modern value by several meters in the XI-XII centuries, which has led to the flooding of large areas in the bottom of the Rostov hollow. Predicting lake level changes and their geomorphological consequences require understanding the links of the climate system with the dynamics of the hydrological regime and exogenous processes in the basins. Establishing such linkages is impossible without a detailed paleoreconstructions of environmental conditions, that are planned to be obtained ih the framework of this project.
During the implementation of the project it is planned to carry out studies of the bottom sediments of the lakes and of the terrace complex structure employing manual drilling and georadar profiling. To determine the genesis and age of the terraces located on the sides of the lake basins, a study will be made of their geological structure by drilling and trenching. Detailed surveying using DGPS and aerial photography with an unmanned aerial vehicle will allow clarifying the topography of the terraces, based on which the reconstructions of high levels of the water stands in the lakes will be made. An important phase of the project will be determining the age of the deposits by radiocarbon and OSL dating. It is planned to carry out studies of the material composition: determination of the content of organic matter and carbonates, granulometric analysis, gross chemical analysis by the XRF method. For the purpose of reconstruction of the trophic status of reservoirs and indirect receiving depth data and flowage are fulfilled diatomaceous complex analysis and biological analysis (for Corday procedure, 1960).
The institution where the project will be implemented, the Institute of Geography of the Russian Academy of Sciences, has all the necessary equipment and technical means to complete all the stated tasks. The project leader possesses all the necessary experience in terms of fieldwork, laboratory work etc. in the specified scientific area. Some previously collected material is already available form the study area: at the initiative of Dr. E.A. Konstantinov in 2017-2018 field work was carried out in the basins of the Nero and Pleshcheevo lakes. Manual drilling carried sediments of lakes with ice, made surveying and drilling on the terraces of Lake Nero. Received a total of 14 columns of undisturbed sediment total footage - 70 linear meters, drilled 11 wells on the terraces of the south-eastern edge of the Lake Nero basin.
The announced reconstruction of the history of fluctuations in the lakes of Pleshcheyev and Nero, carried out at the modern methodical level, will make a significant contribution to the paleolimology of the central part of EEP. The resulting materials were published in peer-reviewed international journals allow replenish global and regional databases on paleolimnology and ecosystems stories (NOAA, PBDB, Neotoma Paleoecology Database, PaleoLake et al.).
The expected results
1. Developing a scientifically-based reconstruction of the level fluctuations of the largest lakes in the central part of EEP (Lake Pleshcheevo and Lake Nero) for the past 20 thousand years.
A great interest in lakes from paleoecologists around the world is due to the fact that the components of the hydrological regime of lakes, which are very sensitive to climate change, can be reconstructed by studying lacustrine sediments. The slightest changes in the level, temperature, salinity, degree of flow, trophic status, and other components are reflected in the composition of the lake sediment - a unique continental natural archive, which, in its detail, the latitude of the chronological coverage and the geography of distribution, is unrivaled. Paleohydrological reconstructions based on the use of modern instrumental methods can be viewed as an integral part of the evolutionary approach to the lake studies all around the world. Such reconstructions were made previously for the many lakes in North America, Central and Western Europe, Central Asia and other regions. As a result, our views about the changes in the hydrothermal regime on Earth over the past 10-100 thousand years were significantly refined (Magny, 2004, Bradley, 2013; Jones, Jordan, 2013; Yu et al. 2013; Cohen, 2017; Wennrich et al., 2016). Moreover, the key indicator of climate change in a large number of works is precisely the fluctuations in the level of lakes - the resultant parameter reflecting changes in the water balance. Reconstruction of the history of fluctuations in the lakes of Pleshcheyev and Nero, carried out at the modern methodical level, will make a significant contribution to the paleolimology of the EEP Center, where the level of study of the history of lakes is much lower compared to, for example, Western and Central Europe. The materials obtained, published in international journals, will allow replenishing global and regional databases on palaeolinology and the history of ecosystems (NOAA, PBDB, Neotoma Paleoecology Database, PaleoLake, etc.).
2. Identifying the relationships between the lake-level fluctuations and the climatic fluctuations in the Late Pleistocene and the Holocene.
There are still gaps in understanding the response of complex geosystems (including large lake basins) to the climatic change. One common approach to the solution of this problem is the paleo-analogue method (Budyko, 1987; Velichko, 1991). This method consists of searching for specified parameters in climate conditions of the geological past and determining the response of the individual components of geosystems to these conditions. Since the course of climate change over the last 20 thousand years has been reconstructed in great detail for the territory of Europe (Masson-Delmotte et al., 2013; Hoogakker et al., 2016; Novenko et al., 2015), we are able to use this interval to search for climatic paleoanalogues of predicted climate warming (IPCC, 2013), which will determine the response of the lake basins to the forthcoming warming. The Holocene optimum (the Atlantic period) can be considered as such paleoanalogue since the average temperature for the central part of the EEP exceeded the modern values by 1-2o C during that period (Velichko et al., 2009). Obtaining that result will create fundamental basis that will enable predicting the reaction of geosystems to the expected climate changes, matching the highest worldwide standard of research in this field of science.
3. Establishing the trend of the change in the average level for the lakes in the central part of the EEP over the prospective climate change during the following century and estimating the probability of intensification of dangerous exogenous processes and hydrological phenomena in the shoreline zone of the lakes.
The practical significance of this result is related to the forecasting of the progress of dangerous exogenous processes and hydrological phenomena in the basins of Lake Nero and Lake Pleshcheevo over the course of the anticipated climatic changes. Paleoanalogue method described earlier will form the basis for such forecasting. The problem of the progress of dangerous exogenous processes is even more urgent because of the objects of historical and cultural heritage (architectural ensembles and archaeological monuments of Rostov and Pereslavl-Zalesskiy) in the shoreline zone of the studied lakes. Furthermore, the coastal zone is specifically the most vulnerable element of the landscape where during the fluctuation of the water level can such processes as abrasion of the shores, flooding and swamping can occur. Therefore, the results of the intended research would eventually aid protecting the population and protecting historical and infrastructure objects from the threats related to the manifestation of dangerous environmental processes.
