1. Shirshov Institute of Oceanology, RAS Comparative analysis of the main ionic composition of hyperhaline lakes: the Aral Sea, the Dead Sea, and Lake Urmia Natalia Andrulionis, Peter Zavialov,
THE MAIN AIMS of THE INVESTIGATION
To obtain of the main chemical composition and density of hyperhaline lakes: the Aral and the Dead Seas and the Lake Urmia. To compare the main ionic composition of hyperhaline waters with each other and an oceanic water.
To determine the salinity of these bodies of water, expressed by the total amount of basic ions.
To compare obtained data of the samples under study with the previously published data.
To obtain densities of the hyperhaline water samples diluted to 35 ‰ and to estimate deviations from Standart Sea Water density (SSW).
The ionic composition of the water is:
Аn important hydrochemical characteristic of a salt water body and an indicator of its quality.
Main ion composition is % of the total salinity of seawater. Main ions are Cl¯⁻, Br¯,SO₄²¯, HCO₃¯, Ca²⁺, Mg²⁺, K⁺, Na⁺
It is important to take into account in the economic use of water.
It plays an important role in shaping the conditions for the functioning of an ecosystem.
It must be taken into account when determining the salinity of water with a non-oceanic ion relation
It affects on physical properties of water (for ex. density, salinity).
M E T H O D S
E Q U I P M E N T
Hyperhaline Lakes before and today
Ion content determination: methods and electrodes
Automatic titrator Metrohm 905 Titrando
Sampling areas in 2017
The Aral Sea
The Dead Sea
Lake Urmia
The automatic titrator 905 Titrando can carry out any kind of potentiometric titration, it is possible to measure the pH, the potential and temperature of the sample and to determine the concentrations using ion-selective electrodes.
Identified ions
Methods
Electrodes
Cl⁻*
Precipitation titration of AgNO3
The combined Ag Titrode Metrohm (glass indicator / silver chloride)
SO4²⁻
Precipitation titration of BaCl2
The ion-selective polymembrane Ba²⁺ (Ecom-Ba) and reference electrode chlorine silver
HCO3⁻
Аcid-base pH titration with HCl
combined pH-electrode Metrohm (measuring glass electrode / silver chloride electrode)
Ca²⁺
Сomplexometric titration EDTA
The Combined Ca⁺ Metrohm polymembrane and reference electrode silver chloride
Mg²⁺
The combined Ca⁺ Metrohm polymembrane and reference electrode silver chloride K⁺
Gravimetric by adding sodium tetraphenylboron
Na⁺
Determination of the difference between anions and cations*
Laboratory density meter Anton Paar DMA 5000M
The method is based on measurement of vibrations of a U-tube which contains the analyzed water. Resonant frequency of the oscillation tube, measured by optical sensors, depends only on fluid density.
R E S U L T S
* Вy the metod is determaned «Сlorinity» i.e. the sum of Cl¯, Br¯ and I¯ recalculated as Chlor.
Estimation of density deviations of the samples of hyperhaline lakes diluted to 35‰ from SSW with a salinity 35‰ in the temperature range from 1 to 29 °C.
Main Ionic Composition of water samples (percentage of the total salt content) were taken in 2017 from different hyperhaline lakes. Сomparison with the Standart Sea Water** .
Comparison of the main component composition of the hyperhaline lakes obtained in 2017 with the previously published data (percentage wise to the sample total salinity)
The Aral Sea data was taken from (1)
The Dead Sea data from (2), (3)
The Lake Urmia data from (4),(5),(6)
Results obtained for hiperhaline lakes samples showed significant differences from ionic composition in the open ocean water.
**The composition of Standard Seawater and the definition of the Reference-Composition Salinity Scale Frank J. Millero, Deep-Sea Research I 55 (2008) 50–72, p.62
C O N C L U S I O N S
Absolute deviation of the diluted to 35 ‰ lakes samples density from SSW density is kg/m³ for the Aral Sea and kg/m³ for the Dead Sea. The plot indicate a dependence of the water density from an ion composition of water bodies.
The results of the comparison of water samples indicate various processes of brine formation and salt precipitation in hiperhaline lakes.
The ratios of main ions of composition of hyperhaline water bodies under study has significant difference between each other and Standard Seawater.
Comparison of our data with previously published data clearly demonstrates the evolution of the component composition over time, the differences in the physicochemical processes of salt deposition in hyperhaline lakes.
3. The difference in ionic composition between Standard Seawater and the considered water bodies results in significant inaccuracies in determination of water density using the EOS-80 and TEOS-10 equation.
(1) P.O. Zavialov and all.// M.: Science, ISBN
(2) Krumgalz B. S., Millero F. J.// Marine Chemistry doi: / (82)
(3) Dead Sea study: Final report. Tel Aviv, 2011.
(4) Alipour S.//Saline Systems doi: /
(5) Kelts K., Shahrabi M. // Palaeogeography, Palaeoclimatology, Palaeoecology. Doi: / (86)
(6) A. Karbassi [et al.] // Journal of Great Lakes Research doi: /j.jglr
A c k n o w l e d g e m e n t
The research is carried out under the support of the Ministry of Education and Science of the Russian Federation, Agreement No. 14.W (sampling), as well as within the framework of the State Assignement, theme No (data analysis). The authors are grateful to Dr. E. V. Yakushev
for providing samples from the Lake Urmia and the Dead Sea.