The Bluestone River that straddles the Virginia-West Virginia border has long been a popular trout-fishing spot, as well as a source of drinking water for nearby towns.
So Virginia environmental officials were stunned when routine sampling turned up something disturbing: Carp in the river were loaded with industrial compounds called polychlorinated biphenyls, or PCBs.
Seeking to unravel the mystery, they followed the river all the way up to the entrance of a rural cave in West Virginia.
The groundwater inside Beacon Cave had PCB concentrations that “were just astronomically high,” said Nick Schaer, a geologist with the West Virginia Dept. of Environmental Protection who helped conduct the sampling. “We were getting numbers many times higher than health-based limits.”
The likely suspect sits directly over the cave--a long-abandoned electric manufacturing plant.
Beacon Cave's pollution is a graphic illustration of the growing problem of surface contamination polluting caves around the country, including some located in national parks and forests.
“The problem is extensive and it’s serious,” said Tom Aley, an expert in groundwater hydrology and president of the Ozark Underground Laboratory in southwest Missouri.
Examples abound, including raw sewage flowing into Shalers Brook inside Mammoth Cave National Park in Kentucky, an animal feedlot in eastern Missouri washing waste down sinkholes into Crevice Cave and dirt runoff from logging activity choking Whispering Canyon Cave at Tongass National Forest in Alaska.
“When caves are threatened, the threats almost always come from surface activity,” said David Culver, a cave expert and biologist at American University in Washington, D.C. “People need to be aware that there’s a subterranean ecosystem and that what happens on the surface impacts these unique ecosystems in a very real way."
The problem is gaining attention because nearly one-third of the drinking water supplies in the United States come from underground streams and springs originating inside caves or passing through them.
In some ways, pollution of caves is inevitable due to the cracks and fissures in the rock surrounding them.
Karst formations, which include caves, sinkholes and other subterranean formations, are slowly carved out of limestone by rainwater. Cracks in this rock allow anything that’s dumped on the ground to travel unfiltered to the bottom.
These karst formations are extensive, lying underneath as much as a quarter of the continental United States.
“It’s a big issue in highly developed karst areas where you have lots of groundwater coming through,” said William Elliott, a cave biologist at the Missouri Dept. of Conservation who has studied caves across North America.
In addition to the threat to drinking water, polluted caves jeopardize some of the Earth's most unusual wildlife, too.
The estimated 50,000 caves in the United States support about 1,100 animal, plant and insect species, almost all of which could not survive outside the cave environment, Culver said. Troglobites are blind animals such as fish and insects that spend their entire lives inside caves, evolving with special senses that allow them to survive in total darkness.
In addition, numerous other species, such as bats, raccoons, cave crickets, salamanders, lizards and snakes, use caves as temporary rest areas or as places to breed and raise their young.
Many cave species are included on the nation’s endangered species list, primarily due to poor water quality.
Aley said the threatened animals should send a warning to people whose drinking water comes from streams flowing through caves.
“If pollution is killing off the snails and arthropods, that ought to be an appropriate warning to the people who also make use of that water. If they can’t live well and prosper, why should we expect people who use the same water to live well and prosper?” he said.
Widespread cave pollution has led some experts to ask whether pollution has played a role in white-nose syndrome – a mysterious disease that has killed more than a million bats in the Northeastern United States.
It’s unlikely pollution caused the disease that’s spreading through caves, said David Blehert, a microbiologist at the U.S. Geological Survey’s National Wildlife Health Center. But the U.S. Fish and Wildlife Service this summer began analyzing bat tissue to determine whether PCBs and other chemicals, particularly those used in pesticides, are contributing to the malady.
“Surface contaminants … could be exacerbating the problem” by weakening immune systems, said Anne Secord, an environmental contaminants specialist with the federal wildlife agency in Cortland, N.Y., who is leading the study. PCBs, for example, are known to suppress the immune cells of animals.
Also, common pesticides such as atrazine, which some studies have linked to altered hormones and feminized wildlife, have long been measured in underground caves and springs.
A common source of cave pollution is human waste. World-famous Mammoth Cave, visited by nearly half a million people a year, was contaminated with sewage from a nearby hotel. Salmonella, most likely from a faulty septic system, was also measured inside nearby Owl Cave.
The National Park Service installed a regional sewage treatment plant in the late 1990s.
In Alaska, dirt runoff from timber operations might have contained diesel fuel and other petroleum products that polluted cave streams and salmon runs in the Tongass National Forest, as well as drinking water sources downstream.
In a rural area of northeast Oklahoma, Twin Cave has been contaminated with 48 compounds, including banned insecticides chlordane and DDT. The suspected cause: illegal dumping of waste down a nearby sinkhole.
“It’s out of sight, out of mind,” Aley said. “There’s this perception we live on top of an infinite filter and that what you dump on the ground will somehow be cleaned up.”
Caves are among the least protected environments in the world, said Penelope Boston, a geo-microbiologist and associate director of the National Cave and Karst Research Institute.
The health of cave species and that of underground water are “intimately” connected, said Boston, who also directs the Cave and Karst Studies Program at the New Mexico Institute of Mining and Technology.