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Tour guide Nancy Toney leads a group down into Horse cave in the south-central town of Horse Cave, Kentucky. She points over a railing at one of the two rivers tumbling below.
“And this is the river that the sewage treatment plant was dumping the sewage into, through that sinkhole. So the water you see would have been black, those rocks would have been black, you would have been able to see clusters of blood worms hanging to all of the rocks,” Toney says.
Today the rivers run clear and clean. And the eyeless white crayfish that disappeared when pollution was killing the cave have made their way back. But it’s been a long haul.
Humans have been leaving their mark on caves for thousands of years. We’ve sheltered in them, told our stories on their walls with paints. In the prohibition-era 1920s, locals even created an entire subterranean nightclub in one of Hidden Cave’s deep-set caverns—complete with orchestra and dance floor. But it wasn’t until recently that people understood that what goes into a cave can come out the other end—with consequences.
“They’re not just simply holes in the ground…”
This is David Foster. He’s head of the American cave conservation association, which is headquartered right above Hidden Cave.
“They’re holes that evolved because rain water was moving through sinkholes and dissolving them and widening them and opening them. And that rain water has to go somewhere. It doesn’t just seep into the ground and continue to the center of the earth. It comes back out in the form of springs,” Foster says.
Foster says that if you contaminate a cave system, you contaminate the springs that emerge from the cave. And because those springs feed our rivers and streams, you’re ultimately contaminating the water we depend on for drinking. Beneath about 40% of Kentucky’s lands is a geological formation called karst. It’s basically limestone that water can easily dissolve—splitting open cracks, forming sinkholes, and eventually caves. Karst doesn’t remove impurities from the water. It lets it pass right through. So Foster says that when he arrived in Horse Cave 20 years ago, run off from homes and industry had taken their toll on the cave.
“What we had was an open sewer, right in the middle of town,” says Foster.
And the pollution was edging its way into the nearby and better known Mammoth Cave system. But money from the Environmental Protection Agency and the National Park Service helped build a regional sewer treatment system that went online in 1989. The cave got cleaner. But other groundwater contaminants were still causing problems.
“Whenever it would rain, we would smell a gasoline odor. And then we went through a period where the EPA had a program where they were removing all the underground storage tanks that had been leaking. And after that got done, we almost never had that problem,” says Foster.
After years of environmental clean up, the cave’s ecosystem has come back. But it will always be a delicate balance. With few species depending on each other in this rare, sun-less environment, it’s easy to tip the scales. Rick Toomey heads Mammoth Cave’s science and learning center. He says that for example aquatic cave animals rely on the organic material in water that backs up from the Green River or from groundwater that seeps into the cave.
“The cave fish, the cave shrimp, the cave crayfish, these organisms eat the organic material itself, or the organic material gets in the cave and grows bacterial slime. We’re very much dependent on that,” says Toomey.
But they’re also vulnerable for that same reason, because in with that organic material could also come toxins, poisons, pollution.
“Household run off is still potentially an issue. It’s still an agricultural area. We have to make sure we work with people on best management practices, trying to reduce the amount of chemical usage,” Toomey says.
Scientists at both Mammoth Cave and Horse Cave monitor groundwater constantly. But caves without national protection or vigilant conservation—caves all over Kentucky—are often still neglected.