DOI: 10.5061/dryad.hj400j2
title: Data from: A review of the defining chemical properties of soda lakes and pans: an assessment on a large geographic scale of Eurasian inland saline surface waters

description: The aim of this study is to evaluate the definition of water chemical
 type, with particular attention to soda brine characteristics by assessing
 ionic composition and pH values on a large geographic scale and broad
 salinity (TDS) range of Eurasian inland saline surface waters, in order to
 rectify the considerable confusion about the exact chemical classification
 of soda lakes and pans. Data on pH and on the concentration of eight major
 ions were compiled into a database drawn from Austria, China, Hungary,
 Kazakhstan, Mongolia, Russia, Serbia, and Turkey. The classification was
 primarily based on dominant ions exceeding an equivalent percentage of 25
 (&gt; 25e%) of the total cations or anions, and the e% rank of
 dominant ions was also identified. We identified four major types: waters
 dominated by (1) Na-HCO3 (10.0%), (2) Na-HCO3 + CO3 (31.4%), (3) Na-Cl
 (45.9%), and (4) Na-SO4 (12.7%), considering only the first ion by e%
 rank. These major types can be divided into 30 subtypes in the dataset,
 taking into account the e% rank of all dominant ions. The major and
 subtypes of soda brine can be divided into “Soda” and “Soda-Saline” types.
 “Soda type” when Na+ and HCO3– + CO32– are the first in the rank of
 dominant ions (&gt; 25e%), and “Soda-Saline type” when Na+ is the
 first in the rank of dominant cations and the sum of HCO3– + CO32–
 concentration exceeds 25e%, but it is not the first in the rank of
 dominant anions. Soda-saline type can be considered as a separate
 evolutionary stage between Soda and Saline types respect to the
 geochemical interpretation by saturation indexes of brines. The obtained
 overlapping ranges in distribution demonstrate that a pH measurement alone
 is not a reliable indicator to classify the permanent alkaline “soda type”
 and various other types of temporary alkaline waters.
description: Repository_data_EB_MK_2018Major ion concentration data including sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl–), sulfate (SO42–), bicarbonate (HCO3–), carbonate (CO32–), and pH (if it was coupled with ion data) were compiled into a database. The data were drawn from a large geographic scale across Eurasia (Austria, China, Hungary, Kazakhstan, Mongolia, Russia, Serbia, and Turkey) and from a large number of saline lakes and pans (N = 220) with a minimum of 1.0 g L–1 salinity threshold. The 1.0 g L–1 salinity threshold was selected on the basis of a former study [27], where this threshold was experimentally found to be the characteristic boundary of soda ecosystems. Salinity (TDS) was estimated by the sum of major ion concentrations (Na+, K+, Ca2+, Mg2+, Cl–, SO42–, HCO3–, and CO32–) and 1 mg L-1 accuracy was used for all input concentration data independently of the theoretical accuracy of original measurements, therefore decimals were rounded to integer value. As generally known, sodium is by far the most common cation in saline lakes and necessarily the dominant cation in soda type of lakes [1]. Therefore, sites with the most abundant ion other than Na+ were excluded from the dataset. If seasonal or annual water data were available, we used mean values for the database. Most of the data came from papers [1,15,26-39] published in the period from 1956 to 2017. However, we cannot estimate a reliable universal accuracy and reproducibility for all data in this study, because none of the published papers reviewed provide data on uncertainty, furthermore, several of them were carried out by different kinds of national standard methods of ion concentration measurements, but all of them are based on the same international methods of ICP-MS for cations (ASTM 3500-Na-C, -K-C, -Ca-C, -Mg-C), alkalinity titration (ASTM 2320 B), chloride argentometric titrimetry (ASTM 4500-Cl-B) as well as sulfate ions turbidimetry (ASTM 4500-SO42-E). The large geographic distribution of the lakes and pans assessed in the dataset can be seen in the Fig. 1 by countries and references. The collected published data were supplemented with some unpublished sample series in the case of Mongolia and Kazakhstan. Coordinates, countries, sites, pH, and ion composition (e%) data of these additional sites are listed in Appendix 1. pH was measured on site using a WTW multiline field instrument with a SenTix 41 electrode. The samples were filtered through GF5 glass fiber filters (0.4 μm nominal pore size) in the laboratory. For the determination of cations (Na+, K+, Ca2+, and Mg2+), samples were analyzed with the EPA 6020 standard method of inductively coupled plasma mass spectrometry [40] with 2% accuracy. Anion concentrations were measured according to Hungarian standard analytical methods (MSZ). Chloride ion concentration was determined by the argentometric method (MSZ 448-15:1982). Sulfate ion was precipitated in a strong acidic medium with barium chloride, and the resulting turbidity was measured photometrically at 405 nm and compared with standard solutions (MSZ 12750-16:1998). Alkalinity was determined by titration, and the concentration of HCO3–, CO32–, and OH– ions was calculated using the Hungarian standard MSZ 448-11:1986. All of anions and alkalinity were measured with 5% accuracy.