Conductivity Sensors Flashcards
Freshwater streams should ideally have a conductivity between ____ to ____ uS/cm?
Freshwater streams should range in conductivity from 150 to 500 uS/cm (15-50 mS/cm). This is the best range to support diverse aquatic life.
How does temperature affect conductivity?
The warmer the water, the higher the conductivity.
What does conductivity actually measuring in a body of water?
Conductivity measures the water’s ability to conduct electricity, which provides a measure of what is dissolved in water.
Pure, distilled water is a poor conductor of electricity - but when salts and other inorganic chemicals dissolve in water, they break into tiny, electrically charged particles called ions. Ions increase the water’s ability to conduct electricity.
How does the salinity of water affect the conductivity?
Conductivity increases as salinity increases.
What compounds do not dissolve in water, and therefore would not increase the conductivity?
Organic compounds such as sugars, oils, and alcohols do not dissolve, and do not increase conductivity.
Why would sea or ocean water have high conductivity values?
Because they both contain high levels of salt, and therefore the number of ions is higher, and so is the water’s ability to conduct electricity.
What is specific conductance?
Specific conductance is a conductivity measurement made at or corrected to 25C, as this is the standardized method of reporting conductivity.
How are conductance and conductivity related?
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. 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 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.
What is “practical salinity”?
Practical salinity is the value of the salinity in water determined using the conductivity of the water in an equation.
Salinity measurements based on conductivity values are unitless, but are often followed by the notation of practical salinity units (psu).
What are the 8 major ions found in seawater (with a practical salinity of 35)?
The major ions in seawater are; chloride, sodium, magnesium, sulfate, calcium, potassium, bicarbonate and bromine.
Are the major 8 ions present in freshwater?
Yes they are, just in much lower amounts.
The ionic composition of inland water sources are dependent on:
the surrounding environment, ie is there a farm near by that uses chemicals? Is there industrial operations? People with pools? An auto shop, or area with many vehicles such as a busy road or highway?
What two measurements can conductivity measurements be used to calculate?
Obtaining conductivity can allow you to calculate Total Dissolved Solids (TDS), and the practical salinity.
How are salinity, and therefore conductivity, and dissolved oxygen connected?
The higher the salinity level, the lower the dissolved oxygen concentration.
