Karst topography means a landscape that has underlying limestone as its bedrock where caves, sinkholes, underground rivers, and springs can form. You’ve heard of Mammoth Cave, right? Well, that national park and thousands of other limestone caves around the country we formed because they were located in karst topography. These karst areas also often have direct pathways from the surface down into groundwater aquifers because of how easily water passes through dissolved cracks and channels in the limestone. And why does water pass so easily through this limestone?
It all begins in the clouds. Raindrops that fall from the sky pick up carbon molecules from carbon dioxide in the air as they plummet toward the ground. This combination creates a weak acid known as carbonic acid. Limestone (CaCO3) is a weak base so it reacts with carbonic acid and begins to dissolve along tiny fractures in the rock. Over time, and we’re talking over thousands of years, these cracks get wider to the point where they can actually form massive caves. Mammoth Cave, in Kentucky, is one 400 mile-long example. You can imagine how these caves are underground highways for water. And many of these underground waterways also serve as aquifers for drinking water.
Because water so easily enters and flows through limestone fractures in karst topography, any pollutants that may get mixed with the surface water can do the same. For example, manure spread over fields in regions with karst topography or chemicals applied to fields can easily get washed beneath the surface. This pollution is known as non-point source pollution, meaning that the source is difficult to pinpoint. But, as you will see in the video, cutting edge science now makes it possible to pinpoint many non-point sources. Microbiologists can now perform microbial source-tracking tests to pinpoint specifically where groundwater contamination is coming from. Even more mind-boggling is the fact that, through a method called genetic fingerprinting, scientists can actually determine the animal or human source of groundwater contamination.
Watch the video to learn more about these methods plus use the classroom lesson activities to learn the skinny on karst non-point source pollution in your region. To “spelunker” you way deeper in the hidden world of karst topography and its environmental implications:
- Explore the extended learning section below by clicking on the “Learn More” tab below to discover more
- Or better yet, ask your teacher to download the lessons below so your entire classroom can share in peer-driven learning.
Also, find out more about what you can do to keep your local waters healthy and clean by checking out the website of our educational partner, Wisconsin Land+Water.