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Tracing water through Wind Cave with dye
Wind Cave National Park's visitor-center parking lot drains into the cave below it. Dye traces showed that: dye poured into the south lot's drain showed up in the cave within hours. The finding comes from a series of studies at the park, which sits above the Madison Aquifer, using bright dyes to see where water goes.
Visible fluorescein dye turned the water of Calcite Lake bright green for a short time. NPS photo.
Why trace water
The Madison Aquifer is a large underground source that supplies the park and parts of South Dakota and Wyoming, and where the cave meets it, large lakes form inside the cave. Western South Dakota is relatively dry, so the park has few major surface water sources. They may look insignificant, but the studies show they are shaped by activity outside the park and in turn affect the cave and the aquifer.
Some studies take samples to a lab. A USGS analysis in 2002 and 2003 found chemicals from consumer goods and septic systems in the park's three streams, Beaver, Cold Spring and Highland Creek, which the page reads as outside forces polluting water that flows in.
Dye tracing is another tool. Researchers inject dye into the ground and follow it with dye receptors, small mesh bags holding charcoal. Eyes can spot dye that colors a water source, but a lab can confirm very small amounts. If pollution entered the cave, its rare and fragile ecosystem could be damaged, and polluted surface water reaching the aquifer could make drinking water unsafe.
Pouring dark red rhodamine WT dye into Highland Creek. NPS photo.
The studies
| Study | What was done | What it showed |
|---|---|---|
| Graduate student's study, 1986 | Two traces near the visitor center: fluorescein in the ground in mid-July, rhodamine WT at the south parking-lot drain a month later | Fluorescein in a few spots, later judged probably false positives; rhodamine in a few cave spots a couple of days after injection and in the park's well, though dye from another trace at Beaver Creek was deemed the likely source in the well. No clear results, but it set the foundation |
| 1993 | Rhodamine WT over the Club Room in mid-June; fluorescein over the cave's southeast section a month later | After two years, no dye in any cave sample |
| 1996 follow-up | Dye at and around the 1986 sites | See below |
| 2008, Highland Creek | Rhodamine WT in a hole reported in the streambed that year | No dye in Calcite Lake or the park wells |
| 2008, inside the cave | Fluorescein in What the Hell Lake | A month later dye was visible in all three waters |
The 1993 injections were farther from park facilities, over places where the ground above the cave is very thick. The page reads the lack of dye as meaning either that water flowed along the surface or that underground flow was too slow or complex to reach the cave for years. It also means park facilities sit on a thin part of the ground over the cave, which prompted the 1996 work.
What the 1996 follow-up found
Rhodamine WT and water injected at the south parking-lot drain produced immediate results at a cave site below it. Dye levels rose within hours and began to fall almost two weeks later, then rose again with each rain event and fell as less water entered. With that link known, concern grew about how much parking-lot runoff reaches the cave and what harm it does.
Fluorescein injected at the picnic area used in 1986, and at a few other sites around the northern cave, gave no result in that part of the cave for a year. But the picnic-area dye did show up at the same cave spot where the 1986 false positive had appeared, about 449 meters from the injection site, so water was indeed moving across the land and then down into the cave.
What the 2008 work added
In 2008 a hole was reported in the bed of Highland Creek, in the park's northern section, and the stream's water flowed into it and underground. Lab analysis of the dye receptors showed no dye in Calcite Lake or the wells, so the creek's water does not reach the cave or the park wells.
The other 2008 study tested links among Rebel River, What the Hell Lake and Calcite Lake inside the cave. A month after dye went into What the Hell Lake it was visible in all three, and lab tests of receptors at Rebel River and Calcite Lake confirmed fluorescein. Water from What the Hell Lake flows into the other two, and park wells showed no dye.
Calcite Lake in 2013, long after the dye had left the water. NPS photo.
The summary
Water above ground, in the ground and in the cave is connected. According to the page, that helps show how park buildings and other activity inside and outside the park affect water, and can inform decisions on future developments.
Sources
- National Park Service, Wind Cave National Park, "Following Water Movement Using Dye Tracing" (https://www.nps.gov/articles/000/dye-tracing-wind-cave.htm). The page cites park reports from 2011 and 2012 and a 2015 study of dye tracing through the ground above Wind Cave; names of students and staff are left out; rewritten in hubnx's own words.