Increase in metal concentrations in Rocky Mountain watershed tied to warming temperatures

September 10, 2012

(Phys.org)—Warmer air temperatures since the 1980s may explain significant increases in zinc and other metal concentrations of ecological concern in a Rocky Mountain watershed, reports a new study led by the U.S. Geological Survey and the University of Colorado Boulder.

Rising concentrations of zinc and other metals in the upper just west of the Continental Divide near Keystone, Colo., may be the result of falling water tables, melting permafrost and accelerating mineral weathering rates, all driven by warmer air temperatures in the watershed.  Researchers observed a fourfold increase in dissolved zinc over the last 30 years during the month of September.

Increases in metals were seen in other months as well, with lesser increases seen during the high-flow snowmelt period. During the study period, local mean annual and mean summer increased at a rate of 0.5 to 2.2 degrees Fahrenheit per decade.

Generally, high concentrations of dissolved metals in the Snake are primarily the result of acid rock drainage, or ARD, formed by natural weathering of pyrite and other metal-rich sulfide minerals in the bedrock. Weathering of pyrite forms sulfuric acid through a series of chemical reactions, and pulls metals like zinc from minerals in the rock and carries these metals into streams.

Increased sulfate and calcium concentrations observed over the study period lend weight to the hypothesis that the increased zinc concentrations are due to acceleration of pyrite weathering. The potential for comparable increases in metals in similar Western watersheds is a concern because of impacts on water resources, fisheries and stream ecosystems. Trout populations in the lower Snake River, for example, appear to be limited by the metal concentrations in the water, said USGS research biologist Andrew Todd, lead researcher on the project.

"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 ARD as we consider the management of these watersheds moving forward."

Warmer temperatures and earlier snowmelt runoff have been observed throughout mountainous areas of the western United States where ARD is common, but it is not known if these changes have triggered rising acidity and metal concentrations in other "mineralized" watersheds because of lack of comparable monitoring data, according to the research team.

CU-Boulder Professor Diane McKnight, a collaborator on the project, has generated much of the upper Snake River data through research projects conducted with her students since the mid-1990s. McKnight said students in her environmental engineering and environmental studies classes like Caitlin Crouch—a study co-author who received her master's degree under McKnight—are highly motivated to understand ARD problems. 

"Students can see that their research will have direct applications to addressing a critical issue for Colorado," said McKnight, professor in the civil, environmental and architectural engineering department and a fellow in CU's Institute of Arctic and Alpine Research.

In cases where ARD is linked directly with past and present mining activities it is called acid mine drainage, or AMD. Another Snake River tributary, Peru Creek, is largely devoid of life due to AMD generated from the abandoned Pennsylvania Mine and smaller mines upstream and has become a target for potential remediation efforts.

The Colorado Division of Reclamation Mining and Safety, in conjunction with other local, state and federal partners, is conducting underground exploration work at the mine to investigate the sources of heavy metals-laden water draining from the mine entrance. The new study by Todd and colleagues has important implications in such mine cleanup efforts because it suggests that establishing attainable cleanup objectives could be difficult if natural background metal concentrations are a "moving target."

A study on the subject was published in the journal Environmental Science and Technology.

Explore further: Decrease in Metals Contamination Seen Over the Past 30 Years

Related Stories

Decrease in Metals Contamination Seen Over the Past 30 Years

June 15, 2006

The U.S. report card on metals contamination in sediment is showing marked improvement. A new study has analysed the past three decades of environmental legislation and regulation, changing demographics and land-use practices ...

New research may help to clean drainage from abandoned mines

December 16, 2009

(PhysOrg.com) -- In a quiet green glen near Ashville, Pa., lies a rust-colored pond. A deep, rectangular hole in the ground, it somewhat resembles an Olympic-sized pool. Few people, however, would make the mistake of swimming ...

New study documents cumulative impact of mountaintop mining

December 12, 2011

Increased salinity and concentrations of trace elements in one West Virginia watershed have been tied directly to multiple surface coal mines upstream by a detailed new survey of stream chemistry. The Duke University team ...

Toxic spill from zinc mine in Peru

September 3, 2012

(AP)—Peruvian authorities say wastewater laced with heavy metals from a major zinc mine has spilled into a tributary of the Amazon, contaminating at least six miles of the waterway.

Recommended for you

What would a tsunami in the Mediterranean look like?

August 27, 2015

A team of European researchers have developed a model to simulate the impact of tsunamis generated by earthquakes and applied it to the Eastern Mediterranean. The results show how tsunami waves could hit and inundate coastal ...

Intensity of desert storms may affect ocean phytoplankton

August 27, 2015

Each spring, powerful dust storms in the deserts of Mongolia and northern China send thick clouds of particles into the atmosphere. Eastward winds sweep these particles as far as the Pacific, where dust ultimately settles ...

1 comment

Adjust slider to filter visible comments by rank

Display comments: newest first

VendicarD
5 / 5 (2) Sep 10, 2012
And yet another nail in the coffin of Global Warming Denialists.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.