Deep dive: How WKU’s Crawford Hydrology Lab solves problems underground

Deep in the ground beneath south central Kentucky awaits one of nature’s marvels: the Mammoth Cave system, which, at more than 400 miles, is the world’s longest known cave system.

At any given time, there’s a good chance that researchers from Western Kentucky University’s Crawford Hydrology Lab, led by Chris Groves, Ph.D., are conducting research in this information-rich environment.

Hydrologist and former Crawford Hydrology Lab graduate student, Autumn Turner, analyzes groundwater samples in the laboratory.

“What we primarily do at the Crawford Hydrology Lab is study underground water,” Groves said.

Studies vary in purpose, but common research topics include identifying pollution sources; understanding water resource management and development; and identifying and mapping underground water sources. It’s surprising to think that, in today’s modern age, there are parts of the planet that are still unknown, but that’s the case, including here in Kentucky.

“People are discovering new underground rivers or connections on a regular basis,” Groves said. “Mammoth Cave is still being explored. There’s a whole world that people drive over every day and have no idea it’s there. Our job is to explore this area.”

The lab’s specialty: dye tracing

Due to its location, underground water presents a number of logistical challenges to researchers who want to access these sources.

“Because it’s hidden away, it takes a completely different set of methods to study it,” Groves said.

And that’s where the capabilities of the Crawford Hydrology Lab play a key role in data collection. The lab and its researchers specialize in a technique called dye tracing in which “a fluorescent dye is injected into a well, sinking stream or sinkhole,” according to the Crawford Hydrology Lab’s website. “The route of the dye (and hence the groundwater) is determined by placing charcoal receptors or taking water samples at karst windows, springs, or other karst and surface water features identified from the inventory.”

Dye tracing has proved especially effective in karst areas like that found in Kentucky. These landscapes are formed on certain types of soluble rocks, including limestone, and typically include caves and underground water sources like springs and rivers.

Crawford Hydrology Lab Assistant Director Lee Anne Bledsoe prepares sampling equipment for a groundwater tracing experiment in Kentucky’s Great Onyx Cave.

“You may have a place where water flows like a stream but underground, passing through a cave, then later on it comes back out aboveground in a spring,” Groves said. “Let’s say that spring is a water supply, so if you want to protect that water supply, you need to know if there are sources of pollution that could be flowing into the spring. With a surface river, you could simply look on a map. But if you have a river coming out of a hole in the ground, you can’t tell just by looking at it.”

Although dye tracing has proved effective, it’s a challenging process. As Groves explained, researchers don’t typically know where the dye will emerge, so it’s sometimes difficult to determine where to be to collect water samples. Additionally, when the dye samples do emerge from their underground journey, they’re often in such small concentrations that they’re invisible to the naked eye. That’s why the Crawford Hydrology Lab is equipped with instrumentation to detect dyes. And as a result, the lab has become known worldwide for its dye tracing capabilities.

Initiating a groundwater flow experiment in Mammoth Cave National Park.

“Because we’re one of the few labs in the country that does this, we have clients all over the world,” Groves said.

The benefits of international visibility

The lab’s international reputation has helped bolster three areas of focus: collaboration, student involvement and training.

Studying underground water isn’t isolated to one part of the globe. Instead, researchers worldwide are collecting data from their own nearby karst landscapes. For Groves and the Crawford Hydrology Lab, that means a wealth of opportunities to collaborate with other researchers. One example: the lab team does a lot of work in China and, this November, Groves will make his 37th trip there to meet and work with various research groups. In 2017, Groves received China’s highest award for foreign scientists from President Xi Jinping for “great contributions to China’s hydrogeology and karst geology fields.”

In 2021, Western Kentucky University will host its sixth meeting of scientists and students who come from around the world to experience the Mammoth Cave system and discuss research. This sort of opportunity not only boosts the visibility of the Crawford Hydrology Lab, the WKU campus, and Mammoth Cave National Park, but also gives students a chance to expand their networks on a global scale.

“The most active cave scientists in the world are coming through WKU when they come to see Mammoth Cave, which is really one of a handful of iconic karst landscapes anywhere in the world,” Groves said. “For people who are into it, this is a bucket list event. Plus, our students get to interact with these scientists.”

Crawford Hydrology Lab Director Chris Groves, Ph.D., in Shidong Cave in Yunnan province, China.

Groves and his fellow researchers also frequently take students with them to international conferences and on research trips, additional opportunities for students to meet and network with other students and scientists.

Inside the lab, learning opportunities abound. Students from any school or university can apply for one of two Crawford Hydrology Lab student research grants, which are awarded annually.

“Primarily the grant provides our lab services, including dye, supplies and analysis,” Groves said. “Because Mammoth Cave is near WKU, we have students coming from all over the place and a lot of research going on, so we also make the lab and training available to students in our department.”

Groves and the lab’s research team will also help train other researchers, whether it’s walking them through questions or techniques on a phone call or even sending a full project team to a research site.

An inquiry received by the lab last year is a prime example. A Brazilian researcher reached out to the Crawford Hydrology Lab for help understanding dye tracing. After a conversation, the lab opted to send Assistant Director Lee Anne Bledsoe to Brazil to give a workshop and show the scientist and his colleagues how to work with dye tracing. Splitting the costs made things affordable for both sides, and for everyone involved, it was a win-win.

“We benefit because Lee Anne, in this case, got great new experience and got to see some great caves in Brazil,” Groves said. “Plus, we’re now essentially the go-to team for dye tracing in South America because there are few or no similar labs in that area.”

‘One of the most critical needs in all of science’

The Crawford Hydrology Lab, like WKU itself, maintains a focus on applied research — or, in other words, problem-solving.

For the last two decades, Groves and the lab’s research team has collaborated with other researchers around the world, particularly China, to collect enough data to better understand one piece of what Groves called “one of the most critical needs in all of science: predicting how CO2 levels in the atmosphere will change depending on certain actions.”

First, some brief background. Karst areas are prime for climate change-related studies because of the prevalence of limestone. Limestone contains carbon and, when CO2 gas mixes with water in the atmosphere as rain, it forms an acid that dissolves the limestone. Once water dissolves the rock, it flows underground through caves and tunnels and, eventually, to the ocean.  Some of this CO2 is removed from the atmosphere and ends up dissolved in the ocean.

Graduate student Sean Vanderhoff (background) works with Chinese colleagues on a groundwater sampling plan in Guangxi province, China. (Photo: Chris Groves).

The problem, however, is understanding the quantities and processes.

“Keeping track of he amount of CO2 in the atmosphere is like a bank balance,” Groves said. “You have to know what’s going in and what’s going out.”

The CO2 that’s consumed out of the atmosphere by dissolving limestone is a small amount, but Groves said researchers haven’t yet identified how much it is.

“The whole limestone thing is a relatively small component but, in my view, we need to understand it all,” he said. “Then, we could predict if we do thing X or thing Y or thing Z, what would atmospheric CO2 levels look like in 10 years? We can’t do that now because we don’t understand the chemistry of the processes, much less be able to predict them in the future.”

Those questions lead back to the same source: dye tracing. An essential piece of information is understanding hydrology and sub-surface flow networks — in other words, the ground’s plumbing. Then, researchers could use that knowledge to calculate how much C02 came from the atmosphere and the size of the area over which it’s being dissolved.

“You can’t solve a problem until you understand how something works,” Groves said. “Once we determine how the underground system is functioning, then we can apply that understanding to larger problems, like pollution or climate change.”