Modeling forecasts consistently have demonstrated that the geographic ranges of Rocky Mountain trout species will shrink by some 20 to 90 percent over the next 50 to 100 years as climate change accelerates in the region. Predicted water temperature increases in high-elevation rivers and streams, coupled with reduced water flows, are certain to add to existing stresses for Rocky Mountain trout.

What Models Cannot Do

A native bull trout swims in the cool waters of the Flathead River near Glacier National Park, Montana. The tail end of a native Westslope cutthroat trout can be seen below.

The models themselves, however, don’t provide the regional or local information that resource managers need to take action now to offset the negative effects of climate change on the diversity and abundance of trout species in an individual watershed.

Consequently, USGS researchers and their colleagues at the U.S. Forest Service and Colorado State University wanted to see if closely examining existing and past land-use and habitat changes in five key Rocky Mountain river basins could help provide the kind of detailed, geographically specific information that resource managers need. Over the past century, intensive land use and development have altered some of these aquatic systems, with cascading effects on ecosystems and popular trout fisheries.

The importance of the study’s findings, published in the scientific journal Fisheries, stems from the fact that the analyses did not include predictions into the future, but were driven by real observations across the western United States.  The analyses are the result of actual data across some of the coldest regions of the lower 48; they give a glimpse of what is likely to occur in the future.

Under a rapidly changing climate of the Rocky Mountains, the authors wrote, many trout populations and species will be able to adapt, but others, overwhelmed by future changes, will not survive.

“It’s not enough to know that significant habitat reductions are expected to occur for native trout of the Rocky Mountains over the next 50 to 100 years,” said Clint Muhlfeld, a USGS scientist and co-author on the paper.  “To help native trout species survive into the future, managers need solid scientific information to take decisive action now.”

River Basins and Trout in the West Already Impacted by Climate Change

The researchers assessed five river systems of the Rocky Mountain west where native trout and climate have been documented: the Flathead River Basin in northwest Montana and southeast British Columbia, the Boise River Basin in central Idaho, the Green River Basin in western Wyoming, the Rio Grande Headwaters Basin in southern Colorado, and the rivers and streams of the Greater Yellowstone Ecosystem in Montana and Wyoming.

Because climate change has been ongoing for multiple decades, although at a slower pace than forecasted for the future, the study showed that it is already possible in many instances to see the early indications of stream ecosystem responses to climate change and to use that information to make decisions about the future. It also demonstrated that the importance of different kinds of stressors varies from basin to basin and depends on local factors.

“Most exciting, however, is that the study clearly illustrates that real data are available now that can be used to understand the local effects of climate change and how those changes threaten native trout populations,” Muhlfeld said. “With that information, managers can take science-based actions that can be refined as more information becomes available through time.”

Warmer Temperatures, Earlier Snowmelt, and Reduced Summer Flows the New Norm

On Iceberg Lake in Glacier National Park, ice from the glacier is breaking up and melting at a rapid rate. Cold, glacier fed waters provide crucial habitat for native aquatic species such as trout, and as the ice is disappearing, so are the ideal habitats to sustain native ecosystems.

The researchers found that the average annual air temperature had increased across all five of these basins over the last 60 years, that spring snowmelt runoff is also occurring sooner, that streamflows in summer are lower, and that winter flooding is increasing in some areas.  All of these findings, said Muhlfeld, have important implications for the future of Rocky Mountain trout fisheries.

In fact, noted Muhlfeld, Rocky Mountain trout populations in all of the river basins they studied are already exhibiting signs of stress, such as having to migrate farther upstream to find more suitable habitat, competing with invasive species for habitat and food, and hybridizing with some invasive fish species. Other stresses include a greater risk of eggs being washed away from increases in winter flooding, increased wildfire risks in streamside ecosystems, and reduced summer habitat due to lower flows.

Fishing as Part of the National Heritage Affected

“Fishing in our national parks and charismatic streams such as the Yellowstone River is part of our heritage,” added Robert Al-Chokhachy, another USGS scientist who co-authored the paper. “The  increase in angling closures over the past decade due to the effects of higher temperatures and reduced streamflows also illustrates how climate shifts are likely to have profound socio-economic impacts,” Al-Chokhachy added.

Where to Go From Here

The authors emphasized that it is still early enough that fast-acting, proactive management decisions over the next few decades will minimize losses of these economically and ecologically important trout populations during this transitional century.

“The challenge now is to identify what actions are possible to mitigate the effects of climate change in order to provide these fishes with an opportunity to adapt,” Al-Chokhachy said.

This study was funded by the USGS National Climate Change and Wildlife Science Center, which is helping meet the challenges of climate change and its effects on fish, wildlife and their habitats.

For More Information:

Climate Change and Native Salmonids Collaborative Research Site

Native Fishes of the Northern Rockies

Climate Change in Mountain Ecosystems

(Videocast) Climate Connections: Questions from Glacier National Park, MT

USGS scientist Peter Van Metre examines a parking lot where coal-tar sealcoat has been applied.A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

What is sealcoat?

Coal-tar-based sealant is the black liquid sprayed or painted on many parking lots, driveways, and playgrounds.

Several PAHs are probable human carcinogens, and many are toxic to fish and other aquatic life. Coal tar, which can cause cancer in humans, is made up of more than 50 percent PAHs. An estimated 85 million gallons of coal-tar-based sealant are used on parking lots and driveways each year, primarily in the central and eastern United States.

What are the rates of PAH emissions to the air from coal-tar-based sealcoat?

Coal-tar-based sealants are emitting PAHs into the air at rates that could be greater than annual emissions from vehicles in the United States based on a study in which USGS scientists tracked PAH levels in air and in dried sealcoat following sealcoat application to a parking lot. Two hours after sealcoat application, PAH emissions were 30,000 times higher than those from unsealed pavement. In a second study, USGS scientists measured PAHs in air above parking lots with and without sealcoat, in suburban Austin, Texas. Parking lots with three- to eight-year-old sealant still released 60 times more PAHs to the air than parking lots without sealant.

A USGS scientist adjusts an air pump used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

Children living near sealed parking lots are exposed to PAHs

Children living near coal-tar-sealed pavement are exposed to twice as many PAHs from ingestion of contaminated house dust than from food, according to a separate new study by Baylor University and the USGS. Baylor University scientist Spencer Williams used USGS measurements of PAHs in house dust to estimate the potential ingestion of PAHs by young children living near coal-tar-sealed parking lots. Ingestion of PAHs from food has long been thought to be the primary route by which children are exposed to PAHs. PAH ingestion by children living near coal-tar-sealed parking lots  is estimated to be 14 times higher than by children in apartments adjacent to unsealed parking lots.

Sealcoat is a major source of PAHs to the environment

Past and current  research on environmental contamination and coal-tar-based pavement sealants and implications for human health and stormwater management are summarized in a new Feature Article in the journal Environmental Science and Technology. The article is jointly authored by researchers with the USGS, Minnesota Pollution Control Agency, University of New Hampshire, City of Austin, Texas, and Baylor University.

Bans on coal-tar sealcoat

Some governments have taken action on the use of coal-tar-based sealcoat.  Fifteen municipalities and two counties in four states (Minnesota, New York, Texas and Wisconsin), the District of Columbia and the state of Washington all have enacted some type of ban, affecting almost 10.4 million people. Several national and regional hardware and home-improvement retailers have voluntarily ceased selling coal-tar-based driveway-sealer products.

Coal-tar sealcoat compared to asphalt-based sealcoat

USGS scientists prepare a sampler used to measure emission of polycyclic aromatic carbons (PAHs) into the air.

Two kinds of sealcoat products are widely used: coal-tar-based and asphalt-based.  The coal-tar products have PAH levels about 1,000 times higher than the asphalt products. Coal-tar-based sealcoat is more commonly used in the Midwest, southern, and eastern United States. Asphalt-based sealcoat is more commonly used in the western United States.  Consumers can determine whether a product contains coal tar by reading the product label or the associated Materials Safety Data Sheet (MSDS), available from the applicator, retailer or on the Internet.

For more information, please visit the USGS website on PAHs and sealcoat, or contact Jennifer LaVista.

Agricultural and urban areas contribute to elevated nutrient concentrations

Nutrient sources in both agricultural and urban areas contribute to elevated nutrient concentrations in streams and groundwater across the Nation.

More information