Can someone supply a relationship between conductivity in water and its salinity. That is, is there any formula relating the two quantities?
we can estimate some numbers from formula but, first formula must be changed in different ranges of salinity, for example EC from 10 - 20. the second, according to purity of salt and kind of salt formula is changed.
There is an online conversion calculator at the attached link. Make sure the units are in the form you require. If not, you will need to allow for the change to the units you require.
There is also a link to the source information in Standard Methods for the Examination of Water and Waste Water .
John
http://www.fivecreeks.org/monitor/sal.shtml
According to Fundamental Measurements Environment, the following is the information that could be useful to answer your question.
What is Conductivity?
Conductivity is a measure of water’s capability to pass electrical flow. This ability is directly related to the concentration of ions in the water. These conductive ions come from dissolved salts and inorganic materials such as alkalis, chlorides, sulfides and carbonate compounds. Compounds that dissolve into ions are also known as electrolytes. The more ions that are present, the higher the conductivity of water. Likewise, the fewer ions that are in the water, the less conductive it is. Distilled or deionized water can act as an insulator due to its very low (if not negligible) conductivity value. Sea water, on the other hand, has a very high conductivity.
Figure 1
Salts dissolve in water to produce an anion and a cation. These ions make up the basis of conductivity in water.
Ions conduct electricity due to their positive and negative charges 1. When electrolytes dissolve in water, they split into positively charged (cation) and negatively charged (anion) particles. As the dissolved substances split in water, the concentrations of each positive and negative charge remain equal. This means that even though the conductivity of water increases with added ions, it remains electrically neutral .
Conductivity Units
Conductivity is usually measured in micro- or millisiemens per centimeter (uS/cm or mS/cm). It can also be reported in micromhos or millimhos/centimeter (umhos/cm or mmhos/cm), though these units are less common. One siemen is equal to one mho 1. Microsiemens per centimeter is the standard unit for freshwater measurements. Reports on seawater conductivity use micro-, milli- and and sometimes even just siemen/mho per centimeter, depending on the publication.
Specific Conductance
Specific conductance at 25 degrees C is used as a standard of comparison for different water sources as conductivity ratios change with temperature.
Specific conductance is a conductivity measurement made at or corrected to 25° C. This is the standardized method of reporting conductivity. As the temperature of water will affect conductivity readings, reporting conductivity at 25° C allows data to be easily compared. Specific conductance is usually reported in uS/cm at 25° C.
If a conductivity measurement is made at 25° C, it can simply be reported as the specific conductance. If a measurement is made at a different temperature and corrected to 25° C, then the temperature coefficient must be considered. The specific conductance temperature coefficient can range depending on the measured temperature and ionic composition of the water. A coefficient of 0.0191-0.02 is commonly used based on KCl standards. NaCl-based solutions should have a temperature coefficient of 0.02-0.0214 .
Figure 2
Resistivity
conductivitiy_ohm_mhoConductivity is formally defined as the reciprocal of resistivity, which is worth elaborating on 3. Resistivity is a measurement of water’s opposition to the flow of a current over distance. Pure water has a resistance of 18.2 Mohm*cm 5. Resistivity decreases as the ionic concentration in water increases. A fun way to remember that resistivity and conductivity are reciprocals (1/measurement) is in the unit name – mho and ohm are the same letters, in reverse.
Conductance
Conductance is part of conductivity, but it is not a specific measurement on its own. Electrical conductance is dependent on the length of the conductor, just as resistance is. Conductance is measured in mhos or siemens. Conductivity is the conductance (S) measured across a specified distance (1 cm), which is incorporated into the units (S/cm). As such, the conductance of water will change with the distance specified. But as long as the temperature and composition remains the same, the conductivity of water will not change.
What is Salinity?
Salinity is an ambiguous term. As a basic definition, salinity is the total concentration of all dissolved salts in water. These electrolytes form ionic particles as they dissolve, each with a positive and negative charge. As such, salinity is a strong contributor to conductivity. While salinity can be measured by a complete chemical analysis, this method is difficult and time consuming. Seawater cannot simply be evaporated to a dry salt mass measurement as chlorides are lost during the process.
The most common ions in sea water.
Figure 3
More often, salinity is not measured directly, but is instead derived from the conductivity measurement. This is known as practical salinity. These derivations compare the specific conductance of the sample to a salinity standard such as seawater. Salinity measurements based on conductivity values are unitless, but are often followed by the notation of practical salinity units (psu).
There are many different dissolved salts that contribute to the salinity of water. The major ions in seawater are: chloride, sodium, magnesium, sulfate, calcium, potassium, bicarbonate and bromine. Many of these ions are also present in freshwater sources, but in much smaller amounts. The ionic compositions of inland water sources are dependent on the surrounding environment. Most lakes and rivers have alkali and alkaline earth metal salts, with calcium, magnesium, sodium, carbonates and chlorides making up a high percentage of the ionic composition. Freshwater usually has a higher bicarbonate ratio while seawater has greater sodium and chloride concentrations.
Absolute Salinity
The Gibbs function is the basis of calculating absolute salinity. It considers the entire system as a whole instead of relying solely on conductivity.
While the Practical Salinity Scale is acceptable in most situations, a new method of salinity measurement was adopted in 2010. This method, called TEOS-10, determines absolute salinity as opposed to the practical salinity derived from conductivity. Absolute salinity provides an accurate and consistent representation of the thermodynamic state of the system. Absolute salinity is both more accurate and more precise than practical salinity and can be used to estimate salinity not only across the ocean, but at greater depths and temperature ranges. TEOS-10 is derived from a Gibbs function, which requires more complex calculations, but offers more useful information.
Figure 4
Salinity Units
The units used to measure salinity fluctuate based on application and reporting procedure. Parts per thousand or grams/kilogram (1 ppt = 1 g/kg) used to be the standard. In some freshwater sources, this is reported in mg/L,. Now salinity values are reported based on the unitless Practical Salinity Scale (sometimes denoted in practical salinity units as psu) 22. As of 2010, an Absolute Salinity calculation was developed, but is not used for database archives 24. Absolute salinity is reported in g/kg and is denoted by the symbol SA. TEOS-10 offers pre-programmed equations to calculate absolute salinity.
Figure 5
The different methods and units of salinity measurements all rely on a reference point of 35 for seawater.
The units psu, ppt and SA g/kg are nearly equivalent (and often interchanged) 6. All three methods are based on an approximate salinity value of 35 in seawater. However, there are some distinctions that must be made.
Practical salinity units are dimensionless and are based on conductivity studies of potassium chloride solutions and seawater. These studies were done with 32.4356 g/kg KCL solution and “Copenhagen water” which has a chlorinity of 19.374 ppt. This north Atlantic sea water was given a set practical salinity of 35 psu. The practical salinity scale is considered accurate for values between 2 and 42 psu. These are the most common units used, and practical salinity remains the most common salinity value stored for data archives.
The historical definition of salinity was based on chloride concentration (which could be determined by titration). This calculation used the following equation:
Figure 6
Determining total salinity based on chloride concentrations in only accurate in water sources with a known chloride-salinity ratio, such as seawater.
This method is only acceptable for seawater, as it is limited in estuaries, brackish and freshwater sources. While salinity and chlorinity are proportional in seawater, equations based on this are not accurate in freshwater or when chlorinity ratios change.
Absolute salinity in g/kg is best for studies that require very precise data. It is consistent with other SI units as a true mass fraction, and it ensures that all thermodynamic relationships (density, sound, speed and heat capacity) remain consistent. These units also help determine specific ions’ contributions to salinity values. Absolute salinity also offers a greater range and more accurate values than other salinity methods when ionic composition is known.
An excel function to perform the conversion can be found here:
nest.su.se/mnode/Methods/spreadsheets/cond%20to%20sal%20converter.xls
Under this link you can find the TEOS-10 equation which is quite forward and easily usable in many programs: http://www.teos-10.org/pubs/gsw/html/gsw_SP_from_C.html
This specific algorithm calculates Practical Salinity, SP, from conductivity, C, primarily using the PSS-78 algorithm. Note that the PSS-78 algorithm for Practical Salinity is only valid in the range 2 < SP < 42. If the PSS-78 algorithm produces a Practical Salinity that is less than 2 then the Practical Salinity is recalculated with a modified form of the Hill et al. (1986) formula. The modification of the Hill et al. (1986) expression is to ensure that it is exactly consistent with PSS-78 at SP = 2. Note that the input values of conductivity need to be in units of mS/cm (not S/m).
For further information take a look at http://www.teos-10.org/pubs/gsw/pdf/SP_from_C.pdf
If you are asking about conductivity to salinity conversion with the oceanography required accuracy, here are the definition and equations of the Practical Salinity Scale 1978:
https://salinometry.com/pss-78/
and here is the online calculator of practical salinity:
https://salinometry.com/ctd-salinity-calculator/
also here is the online convertor of practical salinity to conductivity:
https://salinometry.com/stp-conductivity-calculator/
An equation is given below link-
https://www.phionics.com/2020/12/03/linear-conversion-conductivity-to-salinity/
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