page 22 of the UWP Educator’s Guide to Teaching Students About the Upper Uncompahgre River Watershed (also see contents, introduction & pdf link)
Conductivity: What is It?
Conductivity in lakes and streams generally ranges between 0 to 200 µS/cm, while in major rivers conductivity may be as high as 1000 µS/cm. Very high conductivity (1000-10,000 µS/cm) is an indicator of saline (salty) conditions. Acid mine drainage (AMD) is also characterized by low pH, high concentration of dissolved metals, large values of electrical conductivity (EC), and huge loads of sulphate.
Why Does It Matter?
Conductivity measures how easily electricity flows through water. Just like metal, water can conduct (transport) electricity. This is because there are salts dissolved in the water. If you have pure water with no salts, conductivity will be zero. When a waterway also carries metals from acid mine drainage (like cadmium, copper, magnesium, and arsenic), conductivity measurements may be high.
The salts in rivers and lakes come from rocks that get broken down over time. The types of rock and soil in an area will influence the conductivity of the water. Rocks that break down more easily will raise conductivity.
Seasonal factors:
Conductivity often fluctuates seasonally. As water gets warmer, conductivity goes up. Additionally, if lakes do not receive enough rain or stream water, conductivity increases. This is because evaporation takes water away but does not take salts away.
When ice forms on a lake in winter, the water below may also become saltier because salts are not incorporated into the ice. When the snow and ice melts in the spring, conductivity usually goes down because the meltwater dilutes the concentration of salts.
How is it measured?
Conductivity is best measured directly in the lake or river using a probe with a conductivity sensor. Conductivity is typically measured in microsiemens per centimeter (µS/cm). It can also be measured as specific conductivity – a standardized measure that shows what the conductivity value would be at 25°C.
Teachers: We have just one conductivity wand, so this data will be provided to students for each of the four sites, but they should understand why we measure conductivity.
Source: https://datastream.org/en-ca/guidebook/conductivity
