Introduction. Composition of water is an important hydrochemical characteristic of a salt water body. It is very important in shaping the conditions for the ecosystem functioning. This factor should be taken into account in determining water salinity since salinity measurements carried out by the standard oceanographic equipment using electrical conductivity in the water where the ion ratio is different from that in the oceanic water results in significant errors. Data and methods. The present paper describes the analytical methods for laboratory determining the chlorides, sulfates, calcium, magnesium and total dissolved inorganic carbon concentrations using potentiometric titration, the potassium contentby the gravimetric method. These methods are adapted for hyperhaline waters having the different ion-salt composition as compared with the oceanic one. The method's error (relative deviation) did not exceed 1.7% for halogens, 4% for sulfates, 1.5% for carbonate ions, 0.7% for bicarbonate ions, 4% for calcium ions, 3.2% for magnesium and 1.3% for potassium. Results. The components of main chemical composition of the hyperhaline reservoirs, namely the Aral and Dead seas, and Lake Urmia were obtained. Salinity of these water bodies represented by total amount of the basic ions were determined. Discussion and conclusion. The natural basins under study represent the terminal lakes characterized by high water salinity, which is many times higher than that of the ocean water. The ratios of the main ions in the sources under study differ from each other significantly as well as from the similar ratios in the world ocean.
<p>In terms of water mass, salt lakes occupy 104 000 km3 (47 % of the total water volume of all lakes on the Earth), which is only slightly below that of fresh water lakes - 125 000 km3 (53%). Their waters are of certain economic importance, since they are used as raw materials for the extraction of valuable components and for therapeutic purposes. They also have a great influence on climate formation in the region. The drying out of the lakes entails an increase climate continentality. It also leads to an increase of frequency of dust and salt storms and storms that carry toxic substances over long distances from the source. This negatively affects public health. The drying of the Aral and Dead Seas is one of the largest environmental disasters of the 20th century. The reasons for their drying out are both natural such as global warming and aridization and anthropogenic factors such as diversions of river flows for the economic needs of the population of the regions. A sharp decrease in river runoff leads to a rapid drop in sea level, as well as to sharp interannual changes in the thermohaline structure and chemical composition of water. The annual runoff of the rivers has long ceased to fulfill the water resources of these water bodies.<br>We report the results of water sampling campaigns conducted in the Aral Sea (2014-2019) and the Dead Sea (2017-2019). The main ionic composition, salinity, density and other parameters of the waters of the Aral and the Dead Seas were obtained. We compare the hydrochemical characteristics of these water bodies and their changes during with historical data and with each other. The studied natural water bodies are terminal lakes, characterized by high salinity of water, which is many times higher than the salinity of ocean waters. The ratios of the main ions in the studied sources differ significantly between water bodies, as well as from similar ratios in the oceans. We determined ionic composition of these water samples using potentiometric titrator Titrando 905 (Metrohm). The density of samples was determined by the density meter DMA 5000M (Anton Paar). Currently, the Aral Sea is a complex of separate residual lakes with diverging hydrological and hydrochemical characteristics. The Dead Sea today is divided into two basins, the southern part of which is used for industrial purposes. Significant changes of the ionic composition of water with time were registered in both lakes. However, in the waters of the Aral Sea, these processes are much more intense and rapid than those in than the waters of the Dead Sea.</p>
Введение. Важной гидрохимической характеристикой соленого водоема является компонентный состав вод. Он играет важную роль в формировании условий функционирования экосистемы. Его необходимо учитывать при определении солености воды, поскольку измерение солености стандартным океанологическим оборудованием по электропроводности в водах с соотношением ионов, отличным от океанического, приводит к большим ошибкам. Материалы и методы. Описаны аналитические методы лабораторного определения концентрации хлоридов, сульфатов, кальция, магния, общего растворенного неорганического углерода с помощью потенциометрического титрования, а содержания калиягравиметрическим способом, адаптированные для гипергалинных вод с отличным от океанического ионносолевым составом. Ошибка методов (относительное отклонение) измерения основных компонентов составила не более 1,7% для галогенов, 4% для сульфатов, 1,5% для карбонат-ионов, 0,7% для гидрокарбонат-ионов, 4% для ионов кальция, 3,2% для магния, 1,3% для калия. Анализ результатов. Получены компоненты основного химического состава гипергалинных водоемов: Аральского и Мертвого морей, озера Урмия. Определена соленость этих водоемов, выраженная суммарным количеством основных ионов. Обсуждение и заключение. Исследуемые водоемы представляют собой бессточные озера, характеризующиеся высокой минерализацией вод, которая во много раз превышает минерализацию океанической воды. Соотношения основных ионов в исследуемых источниках значительно различаются между водоемами и отличаются от аналогичных соотношений в Мировом океане. Ключевые слова: ионный состав, компонентный состав, основные ионы, автоматический потенциометрический титратор, Metrohm Titrando 905, гипергалинные озера, Аральское море, Мертвое море, озеро Урмия. Благодарности: исследования были выполнены при поддержке гранта Минобрнауки Соглашение № 14.W03.31.0006 (отбор проб), в рамках темы Госзадания № 0149-2019-0003 (анализ данных). Авторы выражают благодарность д. ф.-м. н. Е. В. Якушеву за предоставленные пробы из озера Урмия и Мертвого моря.
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