During the winter, storms layer the Rocky Mountains with snow that supplies the Western United States’ communities with water during the summer. But snow isn’t the only thing that storms deposit on those mountains.
A team of researchers has revealed that the winter storms that cover the Rocky Mountains with snow also carry contaminants from mines. Their work, detailed in a study published March 26 in the journal Environmental Pollution, sheds light on the ecological consequences of mining activities and how environmental processes circulate metal pollutants.
Led by Monica Arienzo, a researcher in the Desert Research Institute’s Division of Hydrologic Sciences, the team investigated contamination levels of mercury, cadmium, zinc, and antimony in snow across the Rocky Mountains.
“Metal pollution in the Rockies is relatively understudied,” Arienzo said in a Desert Research Institute statement. “Other studies have focused on certain parts, so the fact that we have this transect from Montana to New Mexico makes this study unique.”
In the spring of 2018, Arienzo and her colleagues collected snow samples from 48 locations and analyzed the concentration of metals in each. To determine the amount of metal contaminants originating exclusively from human activity, they compared the quantity of metal contaminants originating in natural dust (e.g., calcium) to the quantity of metals from both dust and human activity.
Their analysis ultimately revealed higher concentrations of metal contaminants from human activity in the snow of the northern Rocky Mountains than in the southern Rockies, including in Montana, Idaho, and Northern Wyoming. The researchers noted, however, that the levels are still within the U.S. Environmental Protection Agency’s safety guidelines for drinking water and aquatic life.
To double-check their results, the researchers compared their findings to the National Atmospheric Deposition Program’s data documenting calcium and mercury in rain from 2009 to 2018—and reached the same conclusion.
“I was surprised by the amount of agreement we saw between all these different data sets we brought together,” Arienzo explained. “The snow samples showed us that contamination is higher in the northern Rockies, and that was really interesting. Looking at mercury contamination over time helped us say that 2018 is not just a fluke. When you start to see these trends that are consistent between different records, it makes you feel more confident that something’s really happening here.”
The researchers reconstructed the movement of snowstorms in 2018 to discover that many of the ones in the northern Rockies had come from the Pacific Northwest, whereas the ones in the southern Rockies came from the Mojave Desert. As a result, they suggest the higher levels of metal contaminants from snow in the northern Rockies come from mines in the Pacific Northwest, Idaho, and Montana.
“Our idea is that the dust from current and historical mining sites gets carried up into the mountains [by storms] and deposited across our study sites,” Arienzo said. “This study shows the importance of continued scientific monitoring efforts,” she concluded, “as well as mitigation of current and historical mining sites.”
Even in the seemingly pristine snow of the Rocky Mountains, humans have left their fingerprints.
