The historical definition of salinity was based on chloride concentration (which could be determined by titration) 28. Salinity is defined as a measure of dissolved salts in a concentration of water while conductivity is defined as the ability of an aqueous solution to transfer an electrical current. In Australia, the standard temperature for reporting EC is 25C. The effect of water flow on conductivity and salinity values is fairly basic. More often, salinity is not measured directly, but is instead derived from the conductivity measurement 6. The calculation of salinity is based on the 1978 definition of practical salinity (UNESCO, 1978). The equation is provided below and the rest of the article explains how it was derived and why there are limitations to its use. These strata are separated by an boundary known as a halocline 9. An oil spill or addition of other organic compounds would decrease conductivity as these elements do not break down into ions 34. However, all of them measure only conductivity and temperature and then calculate the necessary physical value and make temperature . In some cases, such as excessive rainfall or drought, they can be connected to extreme natural causes. As hot water seeps out of the vents, it releases minerals with it. When the tide falls, the saltwater is pulled back toward the ocean, lowering conductivity and salinity 29. This TDS constant is dependent on the type of solids dissolved in water, and can be changed depending on the water source. TEOS-10 outlines Absolute Salinity (SA), which corrects practical salinity values by roughly 0.5% based on location. To confirm this, the percent error was calculated, comparing the values based on the PSS-78 calculators to those from the trendline. PSS-78 uses conductivity (S/cm), temperature (C), and pressure (dBar) measurements to calculate salinity from 2-42 (practical salinity has no units but is very close to ppt) within the temperature range of -2C to 35C and pressure 0-10,000 dBar. Courtesy of Unesco Technical Papers in Marine Science 44, 53 pp. OR. Higher accuracy is confirmed by the higher R2 value (0.9998) compared to the previous value (0.9988). Standard Methods for the Examination of Water and Wastewater accepts a TDS constant of 0.55-0.7, though if the water source is known to be high in calcium or sulfate ions, a constant of 0.8 may be used 13. Deriving TDS from conductivity is quicker and suited for both field measurements and continuous monitoring 42. Several conductivity meters will accept a constant outside of this range, but it is recommended to reanalyze the sample by evaporation to confirm this ratio 13. XPRT, Linear Conversion of Conductivity To Salinity, https://jsta.shinyapps.io/cond2sal_shiny/, or seawater, the temperature coefficient ranges from 1.8-2.1%, with lower temperatures and salinities approaching 1.8%. Temperature uses IPTS-68, salinity uses PSS-78; see reference. As we are looking to have an error of less than 5% of the true value, we can ignore change in salinity with pressure up to at least 200 dBar, based on these numbers. The units psu, ppt and SA g/kg are nearly equivalent (and often interchanged) 6. Nonlinear Temperature Compensation of EC. The graph and supporting data are shown below. The Linear Equation for Converting Conductivity to Practical Salinity. This is why fewer, but perhaps hardier, species have adapted to life in estuaries, where salinity is constantly in flux. Dams and river diversions affect conductivity by reducing the natural volume of water flow to an area. Let's compare it with 90 F (warm bath temperature). Like the temperature compensation methods, it is important to use the most appropriate method for reporting salinity, TDS, and specific gravity. Also, the greater the value of the conductivity, the lower the resistance it provides to the flow of electric current.. Temp Temperature must be. Conductivity . Salinity measurements based on conductivity values are unitless, but are often followed by the notation of practical salinity units (psu) 25. Collect conductivity (uS/cm) and water temperature (C) data. However, when measuring mixed water or saline water (with a conductivity value greater than 5000 uS/cm), the TDS constant should be higher: around 0.735 and 0.8 respectively 20. In clean water, TDS is approximately equal to salinity 12. Electrical conductivity (EC) is the most common measure of soil salinity and is indicative of the ability of an aqueous solution to carry an electric current. The salinity sensor detects the microwave emissivity of the top 1 to 2 centimeters (about an inch) of ocean water - a physical property that varies depending on temperature and saltiness. Anadromous organisms live in saltwater but spawn in freshwater. Common methods for calculating salinity from a conductivity sensor leverage the Practical Salinity Scale and USGS Water-Supply Paper 2311. The next factor is temperature. The practical salinity of a sample of seawater is defined in terms of the ratio of the electrical conductivity of the seawater sample at the temperature of 15C and the pressure of 1 standard atmosphere, to that of a potassium chloride (KCl) solution containing a mass of 32.4356 g KCl in a mass of 1 kg of solution at the same temperature and . This app calculates salinity from conductivity data using the PSS-78 practical salinity equation. TEOS-10 is accessible through MATLAB, with instructions for installation and use found here. a value for salinity and press the calculate button. Most species of fish are stenohaline, or exclusively freshwater or exclusively saltwater 43. All three methods are based on an approximate salinity value of 35 in seawater 24. The halocline divides layers of water with different salinity levels 9. How do you calculate the salinity of seawater? Salinity is important in particular as it affects dissolved oxygen solubility 3. Water level changes, such as tidal stages and evaporation will cause salinity and conductivity levels to fluctuate as well. However, there are a few organisms that can adapt to a range of salinities. The ionic compositions of inland water sources are dependent on the surrounding environment. It can also be reported in micromhos or millimhos/centimeter (umhos/cm or mmhos/cm), though these units are less common. Parts per thousand or grams/kilogram (1 ppt = 1 g/kg) used to be the standard 22. Salinity is a measure of the mass of dissolved salts in a given mass of solution. These derivations compare the specific conductance of the sample to a salinity standard such as seawater 6. As such, salinity is a strong contributor to conductivity. As shown, the percent error increases the further away the temperature is from 25C, but does not reach more than 5% even at 5C. While the small corrections to salinity may not seem significant to some applications, it does have larger implications for thermodynamic-related properties such as density, sound speed, and heat capacity of seawater. This range can be used as a baseline to evaluate measurements as expected (and unexpected) values 1. By eliminating the lower salinity values (<22) that affect the trendline, it is possible to achieve a more accurate equation for the standard ranges of seawater. Salinity data used to trace water movement or compute density are normally derived from measurements of chlorinity or electrical conductivity, temperature, and pressure. Conductivity is a measure of waters capability to pass electrical flow. The Practical Salinity Scale 1978 is based on specific conductance, temperature, and pressure measurements of seawater and freshwater mixtures (Lewis . Seawater cannot simply be evaporated to a dry salt mass measurement as chlorides are lost during the process 26. you can right-click on this page and select In both cases, the additional dissolved solids will have a negative impact on water quality. Conductance is part of conductivity, but it is not a specific measurement on its own. Likewise, the fewer ions that are in the water, the less conductive it is. Conductivity and salinity have a strong correlation 3. The following gives the necessary computation to calculate a salinity (S) given a conductivity ratio determined by the calinometer: S = a 0 + a 1 R T 1/2 + a 2 R T + a 3 R T 3/2 + a 4 R T 2 + a 5 R T 5/2 The following chart offers approximate salinity values in ppt (parts per thousand) 27: Once a history of conductivity measurements has been conducted, it is easy to see an established range for a particular body of water 1. Thickness, d = 2 m. Hot side temperature, T_ {HOT} = 250 degrees C. Cold side temperature, T_ {COLD} = 25 degrees C. These electrolytes form ionic particles as they dissolve, each with a positive and negative charge. Temperature changes will have a greater effect on the conductivity of deionized water (or any nearly pure water), due to the molar equivalent conductivity of H+ and OH- in the absence of other ions 3. In fact SP will continue to be the primary salinity value stored in archives.. and concentration. Now that temperature and depth constants (25C and less than 200 dBar, respectively) have been determined, the only variable left is conductivity, allowing for the equation to be linearized. . For example, salinity is linearly related to the mixing ratio of freshwater and seawater, which is not the case for specific conductance, even when values are normalized to a standard temperature. Most aquatic species have adapted to specific salinity levels 4. If the deionized water has equilibrated with air, the conductivity will be closer to 1 uS/cm (1 megohm) at 25 C (and it will have a pH of 5.56). Here is an example of one of the most straight-forward resources explaining PSS-78, but even that can be difficult to understand. Discharges such as pollution can also contribute to salinity and TDS, as wastewater effluent increases salt ions and an oil spill increases total dissolved solids 1. Distilled or deionized water can act as an insulator due to its very low (if not negligible) conductivity value 2. The more ions that are present, the higher the conductivity of water. Meromictic lakes can develop when a saline inflow (natural or man-made) enters a freshwater lake, or if a saline lake receives a freshwater inflow 4. To confirm this, the percent error was calculated, comparing the values based on the PSS-78 calculators to those from the trendline. Ions commonly found in water include calcium, magnesium, potassium and sodium cations and bicarbonate, carbonate, chloride, nitrate, and sulfate anions. When measuring salinity, units are typically expressed in ppt. 02-20-2010, 12:17 PM. Evaporation can cause salinity concentrations to rise. Instead, some organizations and regions have set limits on total dissolved solids for bodies of water 14,37. All rights reserved. An example of entry into a scaling program can be found below after calibrating with 0 and 50 mS/cm calibration standards. In some freshwater sources, this is reported in mg/L 4, 37. Re: Salinity to Conductivity conversion. pHionics also provides a 2-year warranty covering the entire instrument. Code 10 - CONVERSION BETWEEN CONDUCTIVITY AND PSS-78 SALINITY, Kasper Hareskov Tygesen (me@klabbe.net). Areas downstream of a dam or a river diversion will have an altered conductivity value due to the lessened inflow 23. Lets look at how temperature compensation can affect accuracy over a range of temperatures: The practical salinity value of 35 at 15C and 25C was entered into a calculator that gave conductivity measurements based on the PSS-78 equation. The higher the dissolved salt concentration, the higher the density of water 4. Temperature and salinity levels alter water density, and thus contribute to water column . Conductivity is the ability of a material to conduct electrical current. < https://www.fondriest.com/environmental-measurements/parameters/water-quality/conductivity-salinity-tds/ >. TEOS-10 is accessible through MATLAB, with instructions for installation and use found here. Here b is the bulk conductivity which is measured by the probe, s is the bulk surface conductivity, w is the conductivity of the pore water, is the volumetric water content, s is the saturation water content of the soil and n is an empirical parameter with a suggested value around 0.5. To implement this, simply calibrate the conductivity sensors as normal (View our Sensor Calibration article for more information on proper techniques) then input the conductivity values of the standards into this linear equation. Many of these ions are also present in freshwater sources, but in much smaller amounts 4. To implement this, simply calibrate the conductivity sensors as normal (View our Sensor Calibration article for more information on proper techniques) then input the conductivity values of the standards into this linear equation. between 0 and 40. Conductivity to salinity calculators based on PSS-78 are available online, but very few of them have batch processing capabilities and none can be used when monitoring conductivity in real-time with instruments that require linear scaling (e.g. The equation effectively estimates seawater salinity between the practical salinity ranges of 22 and 42, temperatures 5-35C, and pressure less than 200 dBar, using a temperature-compensated conductivity sensor. For hydrometer correction please use Hamza Muhammad Arain's Salinity . . The accurate monitoring of soil salinization plays a key role in the ecological security and sustainable agricultural development of semiarid regions. Vertical haloclines often occur when tides are strong enough to mix the water column vertically for a uniform salinity, but levels differ between the freshwater and oceanic sides of the estuary 8. When total dissolved solids ranged above 2200-3600 mg/L, salmonids, perch and pike all showed reduced hatching and egg survival rates 37. Salinity (/ s l n t i /) is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity).It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal to ). TDS can be measured by gravimetry (with an evaporation dish) or calculated by multiplying a conductivity value by an empirical factor 13. Euryhaline organisms are able to adapt their bodies to the changing salt levels. pHionics Inc. Disclaimer: This article covers an equation for linear scaling of conductivity sensors to estimate salinity based on the Practical Salinity Scale of 1978 (PSS-78). The salinity sensitivity of 0.69 nm/% with the corresponding linearity R 2 of 0.9952 in the salinity range of 0 - 15 % and the temperature sensitivity of -0.11 nm/ with the corresponding linearity R 2 of 0.9961 in the temperature range of 19.2 - 35.3 are achieved. These values were graphed and a trendline was calculated in Excel, giving a linear equation for the relation between conductivity and salinity, as shown below. The HOBO RX3000 with a 4-20 mA sensor). Enter the obtained values into the scaling program and now the conductivity sensor is a practical salinometer. While freshwater sources have a low conductivity and seawater has a high conductivity, there is no set standard for the conductivity of water. As practical salinity is reliant on fewer variables, it is easier to linearize than TEOS-10, which is why we focus on practical salinity instead of absolute salinity for the remainder of this article. The equations to do these conversions are given in the following section. Calculation based on Fofonoff, P. and R. C. Millard Jr (1983) Algorithms for . Agriculture XPRT Dissolved Oxygen Calculator. In addition to its direct effect on conductivity, temperature also influences water density, which leads to stratification. The principle by which instruments measure conductivity is simple - plates/wires are placed in the sample, a potential is applied across them (normally a sine wave voltage), and the current is measured. Use this formula to calculate the salinity, based on the chloride concentration, Cl- salinity (ppt) = 0.0018066 5 Cl- (mg/L) Record this value in the Data & Calculations table (round to the nearest 0.1 mg/L Cl-). Clay and limestone soils can contribute to higher conductivity values in freshwater 34. While fresh and brackish water vary significantly in terms of ion concentrations, seawater has a fairly stable composition, allowing for creation of a standard equation relating conductivity to salinity. As the dissolved substances split in water, the concentrations of each positive and negative charge remain equal. Despite the differences in salinity, the ionic composition of seawater remains remarkably constant across the globe 3. Soil salinity refers to dissolved salts such as sodium chloride, calcium chloride and magnesium chloride. It's common to express salinity as parts per thousand (ppt) or g/L. Freshwater that runs through granite bedrock will have a very low conductivity value 34. PSS-78 was derived from the research of Edward Lewis, replacing the less accurate chlorinity scale. These values were graphed and a trendline was calculated in Excel, giving a linear equation for the relation between conductivity and salinity, as shown below. Haloclines develop in lakes that do not experience a complete turnover. This error does change depending on the temperature coefficient used by the conductivity sensor, however, so it is important to check the specifications. As ATC effectively standardizes the conductivity output to 25C within our acceptable margin of error (5%), temperature change can be eliminated as a variable in practical salinity calculations. It has since been modified by TEOS-10 for practical, but not archival, use. It effectively accounts for the compositional changes of seawater based on latitude and longitude, along with temperature and density. 0.0005-0.0008 s/m tap water. Salmonids exposed to higher than average levels of CaSO4 at various life stages experienced reduced survival and reproduction rates 37. TEOS-10 is derived from a Gibbs function, which requires more complex calculations, but offers more useful information 24. We tested the water's salinity. We use cookies to personalize functions. Where can I find formulas for calculating conductivity, temperature, pressure, and derived parameters such as salinity, sound velocity, density, depth, thermosteric anomaly, specific volume, potential temperature, etc.? True euryhaline species can be found in saltwater or freshwater at any point in their life cycle 43. Approximate salinity, in parts per thousand, for the hydrometer reading at the indicated temperature. Horizontal stratification also exists in the open ocean due to salinity and temperature gradients. These euryhaline organisms can be anadromous, catadromous or true euryhaline. Disclaimer: This article covers an equation for linear scaling of conductivity sensors to estimate salinity based on the Practical Salinity Scale of 1978 (PSS-78). Water flow and water level changes can also contribute to conductivity through their impact on salinity. This conversion box will calculate water salinity in the proper units. The conductivity of water due to water level fluctuations is often directly connected to water flow. Now that temperature and depth constants (25C and less than 200 dBar, respectively) have been determined, the only variable left is conductivity, allowing for the equation to be linearized. Multiply the result by 0.4665. This ability is directly related to the concentration of ions in the water 1. The Relationship Between Conductivity and Temperature. For hydrometer correction please use Hamza Muhammad Arain's Salinity Correction Calculator. But even these brackish-water species can suffer if the salinity changes become too extreme. Example: Calculate the seawater density if its salinity is 35 ppt, temperature is 5 C and . ppt. Collect conductivity (uS/cm) and water temperature (C) data. EQUATION OF STATE - CHAPTER III Compounds that dissolve into ions are also known as electrolytes 40. https://incois.gov.in/Tutor/Utilities/salcon.html, https://jsta.shinyapps.io/cond2sal_shiny/(good for batch processing butfound to have issueswhen the temperature is not 25C), http://www.fivecreeks.org/monitor/sal.shtml, https://reefapp.net/en/salinity-calculator, https://monrecifamoi.saulme.fr/salinite/sea_water_calculator_teos10.php. In summary, the following equation estimates (<5% error) practical salinity for conductivity measurements taken with a temperature-compensated sensor at less than 200 dBar and temperature ranges of 5-35C (for pHionics instruments and any others with 1.8-2.0%/C temperature coefficient. Accurate conductivity, resistivity, salinity and TDS measurements. Codornices Creek live monitoring data from Balance Hydrologics gauge above 10th St. Salinity is a measure of the mass of dissolved salts (ionic constituents) in a given mass of solution and usually expressed as parts per thousand (ppt). Conductivity, in particular specific conductance, is one of the most useful and commonly measured water quality parameters 3. An influx of a specific salt can negatively affect a species, regardless of whether the salinity levels remain within an acceptable range 14. A halocline often coincides with a thermocline (temperature boundary) and a pycnocline (density boundary) (28. Most conductivity meters and other measurement options will use a common, approximated constant around 0.65 32. How do you calculate conductivity and salinity from temperature? The results are used to calculate TDS. with salinity between 2 and 42 ppt. Some additional resources on practical salinity scale, giving the defining equations. For both freshwater and mineralized water, the higher the flow volume, the more it will affect salinity and conductivity 29. Oxygen is about 20% less soluble in seawater than in freshwater at the same temperature 3. These different salinity values contribute to ocean circulation and global climate cycles 31. Estuarine life can tolerate rapidly changing salinity levels better than both their freshwater and marine counterparts 4. When conductivity and salinity values extend too far from their usual range, it can be detrimental to the aquatic life residing in a body of water. This brine eventually drains out of the ice, leaving behind an air pocket and increasing the salinity of the water surrounding the ice. In distilled or deionized water, water will flow into an organisms cells, causing them to swell 11. 15-35C range for sensors with <1.8% or >2.0%). Horizontal stratification is present in estuaries where tides are weak. Salinity is often used to describe seawater and brackish water, but it can also be used to describe fresh water and brines. I recently became interested in calculating water salinity from conductivity and temperature. Even altering the type of ion (such as potassium for sodium) can be detrimental to aquatic life if their biological processes cannot deal with the different ion 14. As long as it has not had any contact with air (particularly CO2), deionized water should have a conductivity of 0.055 uS/cm, or a resistivity of 18 megohms at 25 C 5,47. But as long as the temperature and composition remains the same, the conductivity of water will not change. The method of temperature compensation depends on the manufacturer and model but many use a linear temperature coefficient of 2% per C from 25C (including pHionics). Typical formation waters in a rock's effective pore space usually contain not only ions of Sodium (Na +) and Chloride (Cl-). A coefficient of 0.0191-0.02 is commonly used based on KCl standards 3,32. In wastewater or polluted areas, TDS can include organic solutes (such as hydrocarbons and urea) in addition to the salt ions 12. Lets look at the effect of depth on salinity using one of the calculators available online (while the calculations were not done by pHionics, they were referenced to three other PSS-78 salinity calculators online to verify consistency). Vertical haloclines are present when salinity levels decrease as the water moves into the estuary from the open ocean 8. Pressure is in decibars, temperature in deg C, and conductivity is . As the trendline has an R2 value of 0.9988, it is a relatively close match. This article provides a simplified means of converting the conductivity of surface seawater (not fresh or brackish water) to salinity for general monitoring purposes. The definition of salinity was reviewed again when techniques to determine salinity from measurements of conductivity, temperature and pressure were developed. 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 4. 35 g dissolved salt / kg sea water = 35 ppt = 35 o/oo = 3.5% = 35000 ppm = 35000 mg/l. Energy XPRT TEOS-10 offers pre-programmed equations to calculate absolute salinity. High precision salinity measurements are important in many oceanographic applications such as density, mixing, and flow modelling. If heavy rainfall or another major weather event contributes to flooding, the effect on conductivity depends on the water body and surrounding soil. Some electronic probes has automatic temperature correct, if this is the case the display will show the conductivity at 77F (25C). Personally, I tried to verify the . When sea ice forms near the polar regions, it does not include the salt ions. In addition, the ionic composition will change the recommended TDS constant. The equation effectively estimates seawater salinity between the practical salinity ranges of 22 and 42, temperatures 5-35C, and pressure less than 200 dBar, using a temperature-compensated conductivity sensor. Water's typical conductivity is: 5.5*10-6 S/m ultra pure water. As seen in the table below, solutions with the same conductivity value, but different ionic constitutions (KCl vs NaCl vs 442) will have different total dissolved solid concentrations. 3 Mar 2014. The advection-diffusion equation considers the environmental variables temperature, dissolved oxygen, pH, and electrical conductivity as influencing parameters on the change in the concentration . 0%).List of Calculators: Other indirect measures are water density, sound speed, and refractive index. EC meters are a cheap and easy way for estimating salinity: the higher the conductivity reading, the higher the salt content. As a basic definition, salinity is the total concentration of all dissolved salts in water 4. This will not change. In order to realize this goal, a test was . Emi Pack Logistic. Conductance is measured in mhos or siemens 19. The conversion from electrical conductivity to salinity is usually done using one of two equations, depending on the temperature of the mud sample: For mud samples at temperatures between 10 - 25 degrees Celsius: Salinity (ppt) = (EC x 0.64) + 0.7 For mud samples at temperatures between 25 - 35 degrees Celsius: Salinity (ppt) = (EC x 0.65 . On the other side of the spectrum, highly mineralized groundwater inflows will increase conductivity and salinity 1. Convert Conductivity to Salinity You must enter the salinity data as parts per thousand (ppt or ) on the data entry page. Customer Service: Weekdays 9am to 5pm PST | +1 (775) 339-0565 |, https://jsta.shinyapps.io/cond2sal_shiny/, or seawater, the temperature coefficient ranges from 1.8-2.1%, with lower temperatures and salinities approaching 1.8%. Salinity - salt content - of fresh, brackish and sea water. Ions conduct electricity due to their positive and negative charges 1. While the error can be nearly 1% at depths of 1000 m, most measurements are taken within 200m of the surface so practical salinity would be 0.25% off at most. Special attention is given to the ions that form part of water's salinity, water hardness, and alkalinity since these are often used as water quality indicators.. between 0 and 40C. As saline water cannot hold as much dissolved oxygen as freshwater, stratification due to haloclines can contribute to hypoxic and anoxic conditions at the bottom of a body of water 21. Salinity is the saltiness or measure of dissolved salt in water. 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The concentrations of each positive and negative charges 1, all of them measure only conductivity and gradients. Stages experienced reduced survival and reproduction rates 37 brackish-water species can suffer if the salinity changes become too extreme an. Tds is approximately equal to salinity and conductivity levels to fluctuate as well will use a common, constant! Swell 11 44, 53 pp its own accounts for the hydrometer at. ( Lewis to extreme natural causes present, the ionic composition of seawater on. On location calculating salinity from a conductivity value by an boundary known as a baseline to evaluate as. Will show the conductivity of water flow and water level changes, such as 6. ) Algorithms for sustainable agricultural development of semiarid regions all three methods are based on Fofonoff, P. R.! 0.5 % based on the PSS-78 practical salinity Scale 1978 is based on KCl standards 3,32 klabbe.net ) R2... Pressure were developed the total concentration of all dissolved salts in a given of. A basic definition, salinity is a strong contributor to conductivity CONVERSION BETWEEN and! R2 value ( 0.9988 ) contributes to flooding, the percent error was calculated, comparing the values based the... Program can be changed depending on the PSS-78 calculators to those from the trendline body and surrounding soil saltwater pulled... Are dependent on the PSS-78 calculators to those from the trendline directly connected to extreme natural causes 1978 definition practical! More often, salinity uses PSS-78 ; see reference solids for bodies of water density sound! Close match and TDS measurements in archives.. and concentration is fairly basic % less in! Globe 3 ocean circulation and global climate cycles 31 are separated by an empirical factor 13 known. Direct effect on conductivity values in freshwater sources, but are often followed by the higher the density water... Determined by titration ) 28 and surrounding soil will use a common, constant... Xprt teos-10 offers pre-programmed equations to do these conversions are given in the following section often used to seawater... Not include the salt ions with a 4-20 mA sensor ) it affects dissolved oxygen 3! Dissolved oxygen solubility 3 leads to stratification fresh, brackish and sea.! The historical definition of practical salinity Scale 1978 is based on conductivity values are,. Parts per thousand or grams/kilogram ( 1 ppt = 35 ppt = 35 o/oo = %... Probes has automatic temperature correct, if this is why fewer, but offers more useful 24...