WV Rivers and partner organizations recently secured a historic agreement with DEP to clean up ionic pollution from coal mining in streams of the Guyandotte River basin. This agreement stems from federal laws requiring the treatment of coal mining pollution so that streams and rivers can support aquatic life, and it’s based on the concept of stream “conductivity.” So, let’s take a step back to consider what conductivity and ionic pollution means, why it’s important, and what we can learn from volunteer monitoring data.

First, a definition: “conductivity” measures the ability of a solution to carry an electric current. It increases when the concentration of charged particles (ions) goes up and decreases when the concentration of charged particles goes down. Conductivity is typically expressed in units of “microsiemens per centimeter (µS/cm),” which is, admittedly, rather obscure. To simplify, a “siemen” is a standard unit of electrical conduction (named for Werner von Siemens, a famous electrical engineer from Germany in the 19th century), and “microsiemen” is 1000th of a siemen. The “centimeter” part simply indicates the distance over which conductivity is measured in a water quality probe. Higher water temperatures also will speed up the rate of electrical conduction, so that’s why conductivity data are standardized to 25 °C (and this is done automatically in most water quality probes).

Why is this important?

Conductivity gives us an index of water purity and pollution because land-use practices often increase conductivity above natural levels. For example, road salts can increase conductivity through chloride ions, and mining runoff can increase conductivity through sulfate ions and other materials. Conductivity can’t tell us about specific ions, but it can provide a useful index of water quality and land-use impacts.

For instance, unimpaired streams in West Virginia typically show conductivities below 150 µS/cm and often below 50 µS/cm. In contrast, streams impacted by mountaintop mining and valley fills often have conductivity levels above 500 or 1000 µS/cm. For example, my prior research has reported such elevated conductivity levels in mining-impacted streams of the Guyandotte River. Unfortunately, such effects appear to last for decades, according to research by Ty Lindberg and colleagues at Duke University.

We also know that high conductivity affects stream ecosystems, starting with benthic macroinvertebrates (the bugs that live at least part of their lives in between rocks on the streambed). Here’s how: larval insects breathe through gills like fish do, and they also export waste products from their blood through gill membranes (yes, gills do more than take in oxygen!). But when conductivity levels exceed a tipping point, wastes can’t diffuse through the gill surface because the ambient water has a greater concentration of ions than inside the animal – and the result is lethal. Such ionic toxicity can occur for many types of stream insects but is most well-known for mayflies (order Ephemeroptera). Moreover, these effects can extend up the food chain because stream insects are important food for many fishes, as trout anglers know full well.

And this brings us to the importance of volunteer monitoring and what we’re learning.

Since 2014, over 150 volunteers have collected thousands of water quality samples in Virginia and West Virginia as part of the Water Quality Monitoring Program with Trout Unlimited and partner organizations. As part of these surveys, over 9,400 measurements of stream conductivity were collected and reported on the CitSci.org project website from over 500 sites. Wow!

The plot below shows the distribution of conductivity data collected so far. You can see that most observations are below 300 µS/cm – and that’s a good thing because that is EPA’s benchmark for impairment in West Virginia streams (excluding karst regions). But we also see that many observations (23%) exceed this value and may indicate impairment due to road salts, mining runoff, or other reasons. Looking ahead, WV Rivers will use these data to evaluate the links between conductivity and land use practices while accounting for natural features in the landscape.