Monitoring Salt in Madison’s Freshwaters
Every week this summer, graduate student Aubrey Wendorff and her undergraduate interns can be found scaling river banks and wading through mud to test the waters around Madison for chloride. Chloride, the anion component of common road salts (NaCl), is dissolved in water and can be measured in the lab from water samples or inferred from sensors equipped with electrodes. When chloride builds up in freshwaters it makes them saltier, reducing habitability for organisms in these ecosystems. In fact, one teaspoon of salt is enough to pollute five gallons of freshwater.
Researchers in Associate Professor Hilary Dugan’s lab have been tracking chloride in Madison waters and across Wisconsin for over a decade and working with the community organization Wisconsin SaltWise to share information with the public. You will likely hear a lot about road salts in the winter, when they are being applied, but the signature of chloride in waterways can be found year-round.
Since 2023, Dugan lab students have been monitoring chloride and conductivity, a proxy for chloride, at USGS (United States Geological Survey) stream gauge stations in many of the inlets to the Madison lakes. Students like Aubrey regularly measure these parameters and clean muck and other debris off the mounted high frequency conductivity sensors for more accurate data. Conductivity measures the concentration of ions, like chloride, in the water. Collecting this data every half hour allows Aubrey to discern pulses of chloride and trends on finer time scales than she can learn by collecting weekly water samples.
Aubrey’s goal is to understand the status of chloride impairment in streams around Madison and their connected lakes. She and her lab are asking big picture questions about salt in our freshwaters- where is it coming from, where is it going, and does it get stuck anywhere along the way? This data set is also uniquely connected to the USGS steam gauge stations. Aubrey hopes their resulting flow information will provide insights into the chloride story, such as how much is entering our lakes at each site. Aubrey and her lab ultimately aim to provide data-driven and informed management recommendations to users of road salts and beyond.
But not all tributaries to the Madison lakes have USGS gauge stations, like Starkweather Creek on the northeast side of Lake Monona. Fortunately, the Friends of Starkweather Creek, which Aubrey sits on the board of, will be able to install flow meters there this year and help fill in that missing piece of the puzzle. Similarly, Wingra Creek, which flows into the southwest side of Lake Monona, has no gauge station.
Aubrey engineered her own sensor stations and deployed them for high frequency data collection over the next few years. Underwater buoys are also deployed in the lakes directly over the winter to collect information during that crucial season for this project.
In addition to the chloride monitoring project, Aubrey is entering her second year of graduate work at the Center for Limnology. Her Master’s project aims to take a closer look at chloride and phosphorus interactions by collecting lake sediment cores and incubating them to manipulate light, temperature, and oxygen. She is hoping to better understand the interaction between chloride and the release of key nutrient phosphorus within lakes and how that might fit into the overall chloride story in freshwater ecosystems.
Aubrey is excited about wading into this research and particularly enjoys identifying cool aquatic insects. Hopefully the waters they live in can remain fresh into the future.