Despite its decline in the past 100 years, mining continues to impact communities around Colorado as contaminated effluence from abandoned mines leaches into local watersheds. However, a new study co-authored by Colorado State University professor William Clements demonstrates a “conservation success story,” signifying how Colorado’s rivers can begin recovering from mining contamination.
The study published in Freshwater Science, analyzed four Western U.S. rivers contaminated by acid mining that experienced parallel recoveries following remediation efforts. Clements’ research focused on Colorado’s Arkansas River as one of the four ecosystems.
“In this study we asked: Is there some commonality with recovery trajectories or are they similar? Indeed, they were,” says Clements, a professor in CSU’s Fish, Wildlife and Conservation Biology department. “In my opinion, they all recovered in a remarkably short amount of time given how grossly contaminated they were.”
The California Gulch, which drains into the upper Arkansas River outside of Leadville, was once an 18-square-mile Superfund site that has experienced significant contamination. When sulfides from the region’s metal mines were exposed to oxygen, it formed acidic solutions that carried mining contaminants downstream and into the water supply — a process known as acid mine drainage. Clements’ 30-year research demonstrates the remarkable recovery of the watershed.
“I think it portends really good news for other streams that have abandoned mines or are affected by them,” he says. “(It) shows that if you can remove that primary source of metal … these systems have a remarkable capacity to turn around in a short amount of time.”
For example, one of Colorado’s most infamous spills, the Gold King Mine near Durango, released 3 million gallons of water laced with heavy metal into the Animas River in 2015, turning the river yellow for miles. At the time, at least 230 mines were still releasing heavy metals into Colorado’s rivers, according to an analysis by the Denver Post.
In the Arkansas River, Clements says, “By the time remediation was completed, the number of species we know are sensitive to metals started to return. It doesn’t look exactly like what other streams in the absence of mining pollution look like, but it got really close — and really improved.”
Comprised of two phases, Clements’ research began with an EPA grant in 1989 and became a collaborative project between CSU, the Colorado Department of Parks and Wildlife and the Environmental Protection Agency. At the time, the Arkansas had less than half the number of species as it does now, he says.
The first phase, from 1990 to 2000, focused on improving the river’s water quality by removing metals from a contaminated drainage source, sampling metal concentrations from Leadville to Buena Vista and introducing aquatic insects. Clements and his research team saw vast improvements in the river’s metal concentrations, resulting in better water quality for residents — and wildlife — across the Arkansas Valley.
The aquatic insects played a vital role in the river’s remarkable recovery, acting as water quality indicators: When metal concentrations dropped, their populations increased. Insects rehabilitated the area’s wildlife from the bottom of the food chain, acting as aquatic subsidies — when aquatic nutrients and energy are transferred to a terrestrial environment — attracting more wildlife, including brown trout, birds and mammals.
The second phase, conducted from 2011 to 2014, focused on restoring habitat for the river’s brown trout population and introduced additional vegetation around the river.
“This study shows how we’re redefining the intimate connection between stream and ecosystem — we’ve always known vegetation plays a really important role in ecosystems,” Clements says.
In 2015, the river was designated as a Gold Medal Trout Stream by the Colorado Wildlife Commission for its outstanding fish quality, signifying how remarkably the river’s health has improved.
Now, Clements hopes his research can be used to address ongoing environmental problems and provide a success story for Superfund sites. The Superfund program, administered by the EPA, has been a subject of ongoing debates, given the agency’s past failures of cleaning up toxic waste and contention over how much environmental damage companies should be liable for.
“This (recovery) demonstrates how effective the Superfund program can be and reflects well on the program,” he says. “Superfund is controversial because it’s a federal government program and people are skeptical of what it can or can’t do. Where we have demonstrated success, we should showcase that.”
The river’s recovery also demonstrates the fragility of riparian ecosystems, and how federal agencies can better address the climate change impacts on previously contaminated rivers.
“We can fix these systems, we can turn them around and improve their health and biodiversity by removing the initial stressor,” Clements says. “But even that residual level of contamination, does it make them more vulnerable to land use changes and climate change?”
As Colorado continues to address mining’s environmental legacies, Clements’ study could prove an effective blueprint for local communities to improve water quality while changing how biologists address the looming threat of climate change in riparian environments.
“The question becomes, we spent lots of time and money cleaning up the Arkansas River,” he says. “What’s it going to look like in 30 to 40 years with less snowpack? Can we demonstrate success if other factors are changing?”
