Simulating thermal dynamics of the largest lake in the Caucasus region: The mountain Lake Sevan

Lake Sevan is the largest freshwater body in the Caucasus region, situated at an altitude of 1,900 m asl. While it is a major water resource in the whole region, Lake Sevan has received little attention in international limnological literature. Although recent studies pointed to algal blooms and negative impacts of climate change and eutrophication, the physical controls on thermal dynamics have not been characterized and model-based assessments of climate change impacts are lacking. We compiled a decade of historical data for meteorological conditions and temperature dynamics in Lake Sevan and used a one-dimensional hydrodynamic model (GLM 3.1) in order to study thermal structure, the stratification phenology and their meteorological drivers in this large mountain lake. We then evaluated the representativeness of meteorological data products covering almost 4 decades (EWEMBI-dataset: 1979-2016) for driving the model and found that these data are well suited to restore long term thermal dynamics in Lake Sevan. This established model setting allowed us to identify major changes in Lake Sevan’s stratification in response to changing meteorological conditions as expected from ongoing climate change. Our results point to a changing mixing type from dimictic to monomictic as Lake Sevan will experience prolonged summer stratification periods and more stable stratification. These projected changes in stratification must be included in long-term management perspectives as they will intensify water quality deteriorations like surface algal blooms or deep water anoxia.

Ushkiani-Project: Preliminary archaeological investigations in the Lake Sevan Region/Armenia

The enclosed landscape around the Artanish Peninsula (Lake Sevan/Armenia) can be seen as a prehistoric terra incognita due to the wholesale lack of archaeological investigations to date. Initial approaches in 2019 – funded by the Gerda-Henkel-Foundation – revealed outlines of the prehistoric settlement patterns which could be placed in relation to gold mining in a clearly delineated natural corridor along this line of superregional communication and trade routes. The intention of the following project is to implement an intensive, holistic-archaeological investigation of the settlement network in the surroundings of the gold mining area and an interdisciplinary attempt to embed these structures within the larger ecological and anthropogenic environment.

Past variations of Lake Sevan (Armenia, lesser Caucasus): documenting climate triggers for the Near East and delivering insights for a sustainable management

<p>To understand the long-term patterns of atmospheric circulation in Eurasia, current paleoclimatic reconstruction syntheses lack accurate data for the Near East. In this semi-arid zone, precipitation is the key factor to be studied that strongly controls ecosystems and human societies. Few data are available from Lake Sevan (1900.52 m above sea level, 1,279 km², 38.2 km<sup>3</sup> as of January 1, 2021), the largest fresh-water lake in the Near East, whose past level variations may document seasonal to millennial precipitation changes.</p><p>We present here the preliminary results of the interdisciplinary Sevan-up Project. Its ambition is to develop a high resolution lake level reconstruction (which is expected to be preserved from the influences of long ecological processes and from human activities) and other climatic proxies (from pollen and molecular biomarker) in view to quantify precipitation changes during the Holocene.</p><p>The Early Holocene climate characteristics (strong seasonality) and environment (prevalence of steppe ecosystems) may raise an analogous model of future conditions in the Near East which will be affected by enhanced continentalism. The study of littoral and deep sedimentary deposits will potentially reveal the consequences of past variations in lake levels on its hydrodynamic functioning and trophic status. These results will give crucial information on how to improve the lake's water management with the goal to reach a sustainable use and a better ecological state. Indeed, seasonal stratification onsets and trophic status dramatically changed since the man-made water-level fall during the Soviet times (40% of its volume).</p>

Assessment of aquatic genotoxicity of the Lake Sevan basin, Armenia using natural bioindicators

Water pollution can cause genomic instability, thereby threatening aquatic wildlife and human health․ For a correct assessment of the impact of the mixture of pollutants, chemical analysis of environmental contaminants should be simultaneously applied with genotoxicity assays. The сomet assay is a sensitive, versatile and extensively used method for genotoxicity assessment in a water environment and was successfully applied in aquatic wild species, including fish and crayfish. Earlier we investigated the genotoxicity of waters of the Lake Sevan basin (Simonyan et al. 2016, Simonyan et al. 2019)․ Lake Sevan is the largest lake of the Caucasus Region, situated in the Republic of Armenia, in the Gegharkunik Province. Water pollution in the lake is a result of both anthropogenic and natural pressures. A combination of comet assay (Tice et al. 2000) and chemical analysis was applied for evaluation of water genotoxicity using gibel carp Carassius auratus gibelio and crayfish Astacus leptodactylus as sentinel organisms. Fish and water samples were collected from the south–southwest of the village Shorzha (40028′33″N and 45014′22″E), Peninsula of Lake Sevan (40033′46″N and 45001′37″E), the estuaries of the Rivers Gavaraget (40025′12″N and 45009′53″E) and Dzknaget (40036′55″N and 44058′13″E). Сrayfish and water samples were collected from the estuary of the River Masrik (40013′25″N and 45038′21″E) and near the villages of Artanish (40027′19″N and 45025′12″E) and Tsapatakh (40024′34″N and 45028′22″E). According to the chemical analysis of waters, the south–southwest of the village Shorzha and the estuary of the River Masrik were chosen as reference sites․ The content of contaminants in water was analyzed according to the standard methods in the Environmental Impact Monitoring Center, Ministry of Environment of the Republic of Armenia. The obtained results showed that the levels of DNA damage were significantly higher in both species in polluted areas than in reference sites. A significant positive correlation between DNA damage in C. auratus gibelio and contents of Al, Fe, Cu and Mn in water was shown. DNA damage in A. leptodactylus correlated with Al, Fe, Cu and Mo. C. auratus gibelio and A. leptodactylus were found to be sensitive mostly to the same pollutants, which indicate that these metals may be of primary concern as contaminants of the studied aquatic environment. Thus, the current study indicates that C. auratus gibelio and A. leptodactylus are sensitive bioindicators for monitoring of water pollution in the Lake Sevan basin.

Holocene vegetation, climate and human impact in steppes around Lake Sevan (Armenia) based on a multiproxy approach: Pollen, NPPs and brGDGTs

<p>In the Caucasus Mountains, the role of human influences and climate changes on steppes expansion over the Holocene is still discussed because this region is poorly documented. This study investigates (1) modern pollen-vegetation relationships in Armenia and (2) changes in vegetation, human activity and climate in the Holocene record of Vanevan peat (south-eastern shore of Lake Sevan) located in Armenia. The last 9700 years are recorded in the Vanevan core. We used a multiproxy approach including XRF, Pollen, Non-Pollen Palynomorphs (NPPs) and branched glycerol dialkyl glycerol tetraethers (brGDGTs) to reconstruct changes in vegetation, human impact and climate. The combination of these proxies is innovative and aims to distinguish the impact of human activities and climate change on vegetation. Modern pollen assemblages from semi-desert/steppe regions of Armenia show an abundance of Chenopodiaceae while meadows steppes, subalpine and alpine meadows are dominated by Poaceae. The Holocene vegetation at Vanevan is characterized by steppes dominated by Poaceae, <em>Artemisia</em> and Chenopodiaceae. However, several arboreal taxa, such as <em>Quercus, Betula, Carpinus betulus</em> and <em>Ulmus</em>, are more developed on slopes between 8600 and 5100 cal BP. Regarding the human impact, the presence of agriculture is attested since 5200 cal BP, largely increases during the last 2000 years cal BP (high percentages of <em>Cerealia</em>-type pollen) and correlates with the occupation periods reported in archeological studies. Palaeoclimate changes at Vanevan are estimated from (1) water level changes (2) temperature reconstructions based on brGDGTs (3) climate reconstructions based on pollen (through a multi-method approach: Modern Analogue Technique, Weighted Averaging Partial Least Squares regression, Random Forest, and Boosted Regression Trees). Climate reconstructions based on pollen and brGDGTs are rare and the multi-method approach using pollen data is innovative in the region. The results of Vanevan give evidence of high temperatures from 7900 to 5100 cal BP and arid events at 6000, 5000-4500 and 4200 cal BP, in agreement with other regional records.</p>

Unusual vertical distribution of zooplankton and fish in the pelagic zone of Lake Sevan during summer stratification

Previous studies in Lake Sevan during summer stratification have shown that the highest zooplankton abundance and biomass was found at the lower boundary of the epilimnion. At the same time, whitefish (Coregonus lavaretus), being main planktivorous species in the lake, preferred the hypolimnion, but was leaving this layer if dissolved oxygen concentrations decreased to 1–5 mg/L. The study was conducted in Bolshoy Sevan (the southern part of Lake Sevan) on July 29–30, 2019. The vertical profiles of water temperature and dissolved oxygen concentration, as well as distribution of major taxonomic groups of aquatic organisms were assessed four times a day: in the dark (night time), in the light (day time), and in twilight (morning and evening). Fish population density was assessed using a “Simrad EK80” echosounder. Vertical distribution of zooplankton and fish observed within the study period did not correspond to that described earlier. Maximal zooplankton biomass during the study was recorded in the hypolimnion, and minimal biomass, in the epilimnion. Most of fish (89–100%) located in the metalimnion. At night, about 10% of the fish population descended to the hypolimnion, despite the low dissolved oxygen concentrations found there (3.0–3.1 mg/L). At dawn, about 7% of the fish ascended to the epilimnion, reaching a 7-m depth, where the water temperature was 20.8 °C. The water temperature range preferred by most fish individuals varied during the observation period and did not correspond to previously reported ranges.

VARIABILITY OF WINTER EXTREME LOW TEMPERATURES OF THE SURFACE AIR LAYER IN THE LAKE SEVAN BASIN (ARMENIA)

The purpose of this work to study, analyze and evaluate the patterns of spatial variability of long-term fluctuations in winter extreme low temperatures of the surface layer of atmospheric air in mountainous territories of Armenia (for example, the lake Sevan basin). To achieve this goal, the results of actual observations by Armhydromet and the available literary sources have been collected, processed and analyzed. As a result of the analysis of the values of extreme low temperatures, it can be noted that the genesis of winter extreme low temperatures is different in the territories under consideration. Winter extreme low temperatures stand out for their uneven distribution – they range from -26.3 to -38.1. For the calculation of winter extreme low air temperatures of unexplored or poorly studied territories, correlations were obtained between the value of extreme low temperatures and the altitude of the area above sea level. In the study area, a tendency towards an increase in winter extreme low temperatures is mainly observed. The scientific novelty of the obtained results lies in the fact that in modern observational materials, for the first time, the regularities of the variability of the spatio-temporal distribution of winter extreme low temperatures of the surface air layer in the lake Sevan basin are estimated. Findings • The study of the patterns of variability of the spatial-temporal distribution of winter extreme low temperatures of the surface air layer under conditions of regional and global climate change is an urgent task of modern geographical science; • Winter extreme low air temperatures are mainly due to the nature of the underlying surface and the features of the relief. The smallest values are observed not in high-altitude zones, but in those places where cold air accumulates (that is, in depressions). In winter, in the hollow valleys, an inversion is mainly observed- in parallel with the height, the air temperature rises. In valleys, as a result of the accumulation of cold air, low temperature conditions can be observed for quite a long time; • The study area is distinguished by a characteristic regime and an uneven spatial distribution of winter extreme low temperatures. They range from -26.3 (Semenovka) to -38.1(Masrik). • Winter extreme low temperatures rise up to 2000-2100m with altitude, and on the contrary, they decrease at altitudes above 2000-2100m. The vertical temperature gradient is -0.5C/100m and 0.8C/100m, respectively; • On the basis of the obtained correlation between winter extreme low temperatures and terrain heights, two regions were identified: 1) heights up to 2000-2100m and 2) 2000- 2100m and higher; • Temporal trends during perennial winter extreme low temperatures are mixed. In the study area, these is a predominance of positive trends. Negative trends are characteristic for the period 1935-1966 at the Sevan, Masrik and Martuni meteorological stations; • In the study area, winter conditions become thermally milder, which should be taken into account when developing strategic programs for the future development of this area.