The potential of using modern methods of numerical simulation and remote sensing for calculating some of the water balance components of the Sivash Bay under the conditions of modern climate change and lack of in situ data from the Genichesk and Chongar Bridge hydrometeorological stations are discussed. The results of calculating the level of the Sivash Bay using modern numerical simulation methods are presented to estimate such water balance components of the bay as the water exchange with the Sea of Azov through the Tonkii Strait. In the paper, there are also some examples of monitoring the water surface area changes in the Sivash Bay and the Sivash reservoirs, the data on which are necessary for water balance calculations using remote methods. The problems in calculating the evaporation from the bay surface as one of the main output components of the bay water balance under conditions of increasing salinity in the bay are considered.

The paper presents the results of studying the spatial distribution of heavy metals (Zn, Cu, Ni, Cr, Sr, Co, Fe, Mn) in the bottom sediments of the bays of the Sevastopol region. The data obtained during the 2003 to 2018 expeditions are analyzed. The spatial distribution and accumulation of heavy metals in the bottom sediments of the Sevastopol, Kazachya and Balaklava bays are studied. Correlations between their content and the physico-chemical characteristics of bottom sediments of the studied water areas (content of Corg, CaCO3, fractional composition) were obtained. The metals with the same correlation coefficients for both the content of Corg and the silt fraction content are identified. These are Fe (r = 0,7) and Ni (r = 0,6) for bottom sediments of the Sevastopol Bay, Fe (r = 0,6) and Cu (r = 0,7) for the Kazachya Bay and only Ni (r = 0,8) for the Balaklava Bay. High correlation between Sr and CaCO3 content (r = 0,8) has been established for bottom sediments of all studied water areas. It is shown that the spatial distribution of heavy metals is determined by physico-chemical characteristics of bottom sediments, which is confirmed by the magnitude of correlations in terms of the content of fine fraction and organic carbon, while the difficult water exchange with the open sea contributes to their accumulation up to maximum values.

The numerical experiments were carried out to assess the hydrodynamic regime of the eastern part of the Sevastopol Bay, subject to the Chernaya River runoff (high- and low-water periods) and the Yuzhnaya Bay, subject to the technogenic load using the hydrothermodynamic block of the numerical three-dimensional unsteady model MECCA (Model for Estuarine and Coastal Circulation Assessment).The simulated hydrodynamic parameters of the selected parts of the Sevastopol Bay were used to analyze the self-purification capacity of their water bodies by calculating the assimilation capacity for inorganic phosphorus. Phosphates suggested as a priority pollutant in municipal and storm runoffs in the water area of the bay and a determining factor of its in the bay eutrophication. At the same time, to neutralize the differences in the water volumes of the studied water areas when calculating the self-purification ability, estimates of the specific assimilation capacity of their ecosystems were obtained.According to the simulations for the eastern apex part of the bay during high-water period, the water circulation in the surface layer contributes to the spread of pollutants throughout the entire water area of the bay. During the low-water period in the eastern part of the bay, currents prevail, directed towards the Chernaya River mouth in the surface and in the bottom water layer both in the northwestern and western wind directions. It contributes to pollutant accumulation in this part of the bay, thus reducing ability to self-purification.Possible reasons for the low self-purification capacity of the ecosystem of the eastern part of the Sevastopol Bay with respect to inorganic phosphorus are analyzed, which are associated both with the volumes of incoming Chernaya River waters during winter high- and summer low-water periods, as well as with the features of the morphometric structure of the water area bottom.For the Yuzhnaya Bay water area, the hydrodynamic regime is defined by a difficult water exchange with the main water area. Ventilation of the waters of the Yuzhnaya Bay is mainly determined by the wind regime, as a result of which the waters are either trapped in the bay or carried out of it, which undoubtedly affects the self-purification capacity of its ecosystem.

The paper considers natural-climatic and anthropogenic factors that determine differences in the self-purification capacity of the Sevastopol Bay ecosystems (its western, central, eastern parts and the Yuzhnaya Bay) in relation to the reduced nitrogen forms (ammonium and nitrites) by calculating the assimilation capacity. The authors took into account the intensity of the input sources of the studied forms of nitrogen, the rate of excretion from the ecosystem, the dynamic situation in the studied water areas and in the entire bay as well as the location of recreational facilities. For the first time, the factors were assessed that provide additional input of reduced forms of nitrogen associated with hypoxia during summer water stratification in local deepened areas in the upper bottom sediment layer, taking into account their particle size distribution. Further, the authors considered accumulation of organic matter and its destruction due to oxidized nitrogen forms and formation of reduced forms thereof. The currents in the central and southern parts of the Sevastopol Bay were calculated using a hydrodynamic model. The calculation results correspond to the current system in the mentioned water areas of the bay according to in situ data at different wind situations in the region. According to the calculations, it is possible that under certain hydrometeorological situations additional amount of ammonium and nitrites would flow from the Yuzhnaya Bay into the central part of the Sevastopol Bay.

To assess the water and salt regime of the Sivash Bay after the overlapping of the North-Crimean Canal in 2014 the integrated approach was used, it includes the expeditionary studies of salinity changes in the Eastern Sivash, mathematical modeling of its hydrodynamic regime and usage of satellite images to keep track of changes in the coastal zone of the bay. Spatial heterogeneity of salinity growth over the entire Eastern Sivash with a gradual increase from north to south is shown. In the Southern Sivash the maximum growth of salinity were noted, it reached 93‰ in November 2018, which was twice than the salinity in 2014. The salinity growth is confirmed by the mathematical modeling of hydrodynamic regime of the bay (currents and level of the bay). According to satellite data, we assessed the changes in the coastline of flooded and drained areas of the Sivash Bay after the North-Crimean Canal overlapping in 2014.

Purpose. Climatic conditions for the winter and spring river floods in Crimea are assessed by the example of the Chernaya River. The scientific literature data permitted to analyze salinity dynamics in the Sevastopol Bay during an intensive flood, which is extremely rare in contrast to the high water cases occurring rather frequently. Methods and Results. Based on the available information and using the analyzed in situ data on the Sevastopol Bay apex and the Chernaya River obtained by the Marine Hydrophysical Institute in 2007-2017, considered are the meteorological conditions for a winter-spring high water. The impact of high water upon the hydrological regime and the ecological state of the Sevastopol Bay apex and the Chernaya River mouth is analyzed. Contribution of a winter-spring high water to pollution of the Sevastopol Bay apex with nutrients is assessed. The ecological state of the bay apex during the peculiar winter-spring high water in February, 2015 is compared to that during the low water in September, 2015. Conclusions. The increased content of inorganic nitrogen during a winter-spring flood should be taken into account while calculating the assimilation capacity of the ecosystem under study and assessing the trophic index. The joint analysis of the expeditionary in situ data and the available information from the scientific literary made it possible to conclude that in course of the last decade, salinity in the Chernaya River mouth gradually increased. This can testify the fact that frequency and intensity of the winter-spring floods tend to go down.

Purpose. The results of the expeditionary studies performed by Marine Hydrophysical Institute in the Sivash Bay waters in spring and autumn, 2018 are considered in the paper. Its aim is to continue comprehensive investigation of the bay after the North Crimean channel was closed in 2014, and to evaluate dynamics of salinity, dissolved organic and total suspended matters in its waters affected by the changed anthropogenic and natural-climatic factors. Relevance of the studies carried out in the bay water area is conditioned by urgent necessity in developing and implementing a modern system of environmental monitoring of the bay. Methods and Results. The data obtained during two expeditions in spring and autumn, 2018 in the Sivash Bay waters including the present borders of the Eastern Sivash wetland are analyzed. At 13 stations, water salinity was determined by the refractometric and pycnometric methods, while the dissolved organic matter and the total suspended matter - by "Kondor" biophysical complex. Conclusions. It is concluded that due to the fact that the North Crimean channel was closed in 2014, salinity of the Sivash Bay water continues to change and its ecosystem is being rebuilt. The observed salinity increase is not the same in different parts of the bay. The highest salinity values were observed in the Southern Sivash and amounted 92-93 %, whereas at the same stations in 2016, this value constituted 55-60 %. During the autumn survey, assessment of seasonal dynamics of the total suspended matter and the dissolved organic matter contents yielded high values of concentrations of these two parameters in the bay. In spring when the dissolved organic matter distribution is more monotonous, the slightly increased total suspended matter content was observed at the stations in the Southern Sivash.

The ecological state of the marine shallow water ecosystem (the case of the Sevastopol Bay) is analyzed by the ratio of assimilative capacity and E-TRIX index depending on the anthropogenic load level for the whole bay ecosystem. As part of analysis, the eastern, central, western parts of the bay were distinguished as well as the Yuzhnaya Bay (southern part). Calculations of the assimilative capacity and E-TRIX index for ecosystems of different parts of the Sevastopol Bay were performed using the in situ data of inorganic nitrogen for the period 1998–2012 obtained from the MHI RAS oceanographic data bank. The paper compares values of ecosystem assimilative capacity calculated for inorganic nitrogen as a prevailing pollutant in municipal and storm wastewaters and E-TRIX trophic index of the sea ecosystem, with the technogenic load and biological process seasonality (warm and cold periods) of nutrient income taken into account. This allowed to properly distinguish water areas, which are most vulnerable in terms of formation of negative ecological events, up to disasters. According to the obtained data, such an area is that of the Yuzhnaya Bay. The second vulnerable water area is the eastern apex part of the Sevastopol bay exposed to the Chernaya River discharge. As the results showed, the situation worsens during winter and spring freshets due to increase in content of inorganic nitrogen forms in the Chernaya River runoff. The ecosystem of the western bay part adjoining the open sea is the safest in terms of nitrate nitrogen assimilative capacity, whereas the central part ecosystem appears to be the cleanest in terms of E-TRIX. The ecosystem most exposed to ecological risks in terms of both indices (assimilative capacity and E-TRIX) is that of the Yuzhnaya Bay (the southern part of the Sevastopol Bay). The observed imbalance of distribution of the calculated trophic index E-TRIX and assimilative capacity in different parts of the Sevastopol Bay is due to various nature of these quantities. The assimilative capacity of an ecosystem is defined by physical, chemical and biological processes given a dynamic removal of pollutants from the ecosystem, whereas E-TRIX is determined, in general, by seasonal variability of nutrient income into the ecosystem.

The paper analyzes peculiarities of formation of the Sivash Gulf coastal area, which manifest at the moment as a combination of abrasive and accumulation processes. The paper gives more details about vegetation coasts (a special coast type related to a specific sedimentation type) defined by reed vegetation development, which is prevalent near clough entries in apexes of ingressive gulfs and “secondary” lagoons. Using data of digital multizonal satellites Landsat 5 and 7 as well as Sentinel-2 L1C, the paper considers dynamics (2014–2020) of reed coast areas in the East and South Sivash after damming the North Crimean Canal in 2014 as a consequence thereof and related increase of salinity in the gulf water area. For comparison, the paper analyzes dynamics of vegetation coast spread as a result of the canal functioning, also reed vegetation area growth up to the 1990s is considered. The ecological role of reed vegetation as a distinctive biotope is shown. It is emphasized that damming of the North Crimean Canal not only led to changes of the gulf salinity regime but also affected its entire ecosystem, including the reed coast, formation of which was promoted by increase of fresh water volume in the gulf water balance. Impact of the North Crimean Canal and its damming in 2014 on change of the reed vegetation area in the East and South Sivash was estimated using satellite data. At the studied zone of Prisivashie, flood plain areas shrank most of all in the Knyazevsky and Balaganovsky Gulfs as well as near the Alekseevskaya extinct lake in the South Sivash. In the Rogachinsky Gulf, despite discontinued drainage, influence of waste waters remains significant. Therefore, reed communities have preserved here best. It is shown that for some water areas shrinkage of areas populated by reed vegetation can considerably slow down provided there are local p ermanent or periodic fresh water sources, e. g. waste waters coming from settlements.

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У Д К 5 5 1 . 4 6 4 ( 2 6 2 . 5 ) И.В.Мезенцева 1 , Е.Е.Совга 2 1 Севастопольское отделение Государственного океанографического института им.Н.Н.Зубова, г.Севастополь 2 Морской гидрофизический институт РАН, г.Севастополь САМООЧИСТИТЕЛЬНАЯ СПОСОБНОСТЬ ЭКОСИСТЕМЫ ВОСТОЧНОЙ ОКОНЕЧНОСТИ СЕВАСТОПОЛЬСКОЙ БУХТЫ ПО ОТНОШЕНИЮ К НЕОРГАНИЧЕСКИМ ФОРМАМ АЗОТА На основе данных мониторинговых наблюдений за содержанием биогенных элементов в морских водах восточной оконечности Севастопольской бухты, находящейся под влиянием стока реки Черной как доминирующего источника поступления биогенных элементов, выполнен расчет скорости удаления минерального азота.Дана оценка способности экосистемы выделенного района к самоочищению в отношении отдельных форм неорганического азота.Сравнительный анализ полученной величины ассимиляционной емкости исследуемой экосистемы с привносом неорганического азота водами реки Черной показал недостаточность способности к самоочищению экосистемы предустьевой акватории Севастопольской бухты.КЛЮЧ Е В Ы Е С Л О В А :

The distribution of biogenic element content (total nitrogen, nitrate, nitrite, ammonium, total phosphorus and phosphate, silicon) and dissolved oxygen in the surface and bottom waters of the Yalta seaport in 2013 – 2017 is investigated. The current ecological state of the water area is estimated in comparison with the state of 2003 – 2012. In the period under study, in the water area the total nitrogen content was noted to increase both in aver-age and maximum values, which occurs on a background of a decrease in the content of inorganic forms (ammonium and nitrate nitrogen) in contrast to the previous period. As a whole the water aeration in the period under study remains insufficient, especially in the surface water layer.

В 2015-2016 гг. были выполнены комплексные исследования подводного плюма, наблюдаемого из космоса в районе основного глубинного стока г. Севастополь. В судовых экспедициях на сетке станций были получены вертикальные гидрологические профили, профили течений и оптических характеристик вод, а также отобраны пробы воды для химического и микробиологического анализа. Работы сопровождались съёмками с бортов различных спутников. Достоверно показано, что плюм представляет собой слои мутных вод, вытянутые вдоль берега на расстояние в несколько километров и локализованные на глубине пикноклина. При подъеме пикноклина к поверхности плюм можно наблюдать в видимом диапазоне из космоса. Анализ контактных данных указывает, что существование плюма является следствием аварийного состояния подводного коллектора сбросовой системы. Это подтверждается и результатами анализа спутниковых изображений. Представлена оценка расположения предполагаемого разрыва трубопровода. В области источника загрязнений происходит отрыв объемов мутных вод от основного слоя и подъем их на морскую поверхность. Воды плюма по химическому составу соответствуют сточным канализационным водам. Существование плюма вблизи берега приводит к неблагоприятным экологическим последствиям, в частности, концентрация ионов аммония в районе плюма в 2 раза превышает предельно допустимую, а данные микробиологических анализов указывают на дестабилизацию микробного сообщества и деструктивные процессы в фитопланктоне, вызванные загрязнением.

Dynamics of the Sivash Bay (the Sea of Azov) water balance under the conditions of varying natural and climatic (precipitation, water exchange with the Sea of Azov, river flow and evaporation), and anthropogenic factors (overlap of the North-Crimean Canal in 2014 and change of nature management) is studied. The basic water balance components in the Sivash Bay are assessed for three periods: the first one (1939-1971) - before the North-Crimean Canal was put into operation (conditionally natural mode of the Sivash Bay waters) - is studied using historical data; the second one (1972-2013) - during active exploitation of the canal under various functioning regimes of the irrigation systems, and the third period (2014-2016) - after the Canal was overlapped - are studied using the in situ data obtained by Marine Hydrophysical Institute and allowing for the modified natural and climatic factors. Intensity of water exchange between the Sivash Bay and the Sea of Azov after the canal was overlapped and the Sivash or the Azov currents became predominant is assessed using the calculation of the water level variations in the indicated areas and taking into account the wind conditions in summer, 2014. It is shown that the eastern winds promote intensification of the Azov water inflow to the Sivash Bay, hence, increasing salinity of its waters. Thus, overlap of the North-Crimean Canal in 2014 makes for a complete reconstruction of the hydrological water regime in the bay and its gradual transition to the conditionally natural state.

The long-term inter-annual and seasonal variability in 1960-2010 is assessed for certain hydrochemical parameters of the surface and near-bottom layers in the Heracleian Peninsula coastal waters on the basis of the analysis of hydrological and hydrochemical data from the Oceanographic Data Bank of Marine Hydrophysical Institute. The performed analysis allowed one to assess the impact of different nature processes on the distribution of phosphate phosphorus and silicic acid by the annual variation of content of these nutrients. It is shown that for phosphate phosphorus this is the impact of biological processes, and for silicic acid - natural processes related to an increase in fresh water inflow due to spring floods and the presence of submarine fresh water sources. The analyzed long-term data represent the values which are mostly averaged and can be used for this water area as background data. Complex oceanographic survey of the Heracleian Peninsula water area, carried out in summer and early autumn of 2015 in the area where deep-water sewage discharge of Sevastopol is located, provided an assessment of ecologic situation in this water area. Surface spots of increased turbidity with abnormal values of temperature, salinity and a series of hydrochemical parameters were found. It is determined that these anomalies are related to the outflow of polluted sewage waters to the surface due to the peculiarities of seasonal thermocline formation in the water area under study and possible leakages in case of sewage discharge line rupture. The need for further environmental monitoring of the Heracleian Peninsula coastal zone for developing the scientifically grounded recommendations for improving the ecological situation in the water area under study is confirmed.

The paper uses the estimates of current ecological state of Sevastopol Bay and its zoning by the level of anthropogenic impact to show the possibilities for using the previously developed methods of calculation of assimilative capacity of the most polluted part of the ecosystem with respect to inorganic forms of nitrogen with the prospect of regulation of routine discharges of pollutants.