Warmer air temperatures in recent years have acted as an accelerator, causing significant increases in zinc and other metal concentrations in the Rocky Mountain watershed from abandoned mine sites, researchers say.
According to a study published in September in the journal Environmental Science and Technology, led by the U.S. Geological Survey and the University of Colorado, Boulder, researchers have observed a "fourfold increase in dissolved zinc over the last 30 years," according to the study.
Rising concentrations of zinc and other metals in the upper Snake River west of the Continental Divide near Keystone may be the result of falling water tables, melting permafrost and accelerating mineral- weathering rates - all driven by warmer air temperatures in the watershed.
"This study provides a fascinating and troubling example of a cascading impact from climate warming as the rate of temperature-dependent chemical reactions accelerate in the environment, leaching metal into streams," said Marcia McNutt, USGS director. "The same concentration of metals in the mountains that drew prospectors to the Rockies more than a century ago are now the source of toxic trace elements that are harming the environment as the planet warms."
High concentrations of dissolved metals in the upper Snake River watershed are the result of acid rock drainage, according to the research. The drainage is a result from past and present mining activities.
"The warmer temperatures cause the rate of reactions to change," said Bruce Stover, the director of the abandoned mine reclamation program with the Division of Reclamation "We're seeing warmer temperatures, so the higher heat input is attending to drive chemical reactions toward dissolving and having more metals in the stream."
This increase concerns researchers because of the impacts on water resources, fisheries and stream ecosystems.
"The upper Snake River is severely impacted - it doesn't support a fishery at present," Stover said. "It's certainly not too late to save this river. It would take many years for the stream to recover, but we've seen good recovery in areas where we've done reclamation projects in the past."
Trout populations in the lower Snake River, "appear to be limited by the metal concentrations in the water," said Andrew Todd, a USGS scientist and lead researcher on the project.
Weathering of pyrite forms sulfuric acid through a series of chemical reactions and mobilizes metals like zinc, carrying them into the stream.
The study, over the last 30 years, supports the hypothesis that increased metal concentrations are due to an acceleration of the buildup of metals, caused by warming temperatures.
"Acid rock drainage is a significant water quality problem facing much of the western United States," Todd said. "It is now clear that we need to better understand the relationship between climate and this drainage as we consider the management of these watersheds moving forward."
The Colorado Division of Reclamation Mining and Safety is conducting underground exploration work at mine sites to investigate the sources of heavy metal-laden waters.
The study conducted by USGS aims to establish attainable clean-up objectives.
The Denver Post published an article Sunday about the threat of lawsuits that could prevent the cleanup of abandoned mines that deposit metals into watersheds and areas like the upper Snake River.
The Environmental Protection Agency's current interpretation of the Clean Water Act says "good Samaritans" and state governments embarking on projects to reduce the contamination of watersheds could be held liable for costs of full-scale cleanups, costing millions of dollars a year to treat toxic water forever, as reported by the Post.
This has prevented partial cleanups that, while not stopping all pollution, could improve water downstream.
Such lawsuits could arise from third-party private citizens, according to Stover.
"The way the Clean Water Act is set up is if a project doesn't obtain 100 percent cleanup, they would be liable for the remaining," Stover said. "We could do something at a smaller scale and get 60 percent cleanup of the area. If someone did that, then they could be liable for the other 40 percent through a third-party citizens lawsuit - so no one is willing to do anything, perfection is the enemy of good."