PDF Version of this ArticleCold water for trout
Joint research by SRS and the U.S. Geological Survey
by Zoë Hoyle
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| Rising temperatures may restrict native eastern brook trout to higher elevation coldwater refuges. (drawing by Duane Raver, U.S. Fish and Wildlife Service, courtesy of Wikimedia Commons) |
The names of southern rivers—Roanoke, French Broad, Neuse, Apalachicola, Tar, Tennessee—are nothing if not evocative. As you read them, you may think first of the long human history of the area, but the rivers and streams of the Southeastern United States are actually better known worldwide for the unique and diverse aquatic ecosystems they harbor.
The Southeast is also an area of rapidly expanding human population and increasing demands for sources of clean drinking water, and in the hot summers, for places to swim, fish, and boat. During severe summer droughts, human demands for water have already come into direct conflict with the habitat needs of aquatic species, pitting state against state, and states against Federal agencies.
Species in these ecosystems—fish, mussels, crayfish, salamanders, especially those dependent on cold temperatures such as native eastern brook trout—are already stressed by recurring droughts and will undoubtedly be impacted further by climate change.
Resource managers in the Southeast are more and more challenged to balance human demands for water quantity and quality with the habitat needs of freshwater aquatic species. Managers have access to national databases and models from multiple sources, but lack both regional data and a framework for addressing species and site-specific questions. To develop strategies and to make decisions designed to minimize the effects of climate change on both humans and aquatic species, managers need more precise science-based tools.
In 2010, the Forest Service and the U.S. Geological Survey (USGS) joined forces in a multiyear project to refine and combine climate and hydrologic models to provide a better understanding of climate effects on freshwater fish and water quality and quantity in the region.
In the Mountains, Cold Water for Trout
T he Southeastern United States is home to many aquatic habitats, ranging from the high-elevation coldwater streams of the Appalachian Mountains to the low-elevation warmwater streams of the Coastal Plains. In the mountains, rising water temperatures may restrict native brook trout to higher elevations; under the most pessimistic climate change scenarios brook trout could largely disappear from their native ranges except in isolated high mountain refuges.
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| SRS research on the relationship between air and water temperature and other conditions will help managers identify coldwater habitats that will be resilient under climate change. (photo by USDA Forest Service) |
SRS scientist Andrew Dolloff leads the Forest Service side of the Forest Service-USGS collaboration in a project that’s based on a larger study Dolloff has been working on with biologists from the National Forest System on the relationship between air and water temperature in mountain watersheds that support coldwater species such as brook trout. This study involves installing paired air and water thermographs (digital thermometers) at the downstream-most point of selected brook trout patches in an area that extends northsouth from Maine to Georgia.
Data from a pilot study in Virginia yielded some interesting results.
"Previous large-scale assessments of the effects of climate change on coldwater fish species used models that assume that the correspondence between air and water temperature stays pretty constant, at about 0.8 to 1.0 degrees," says Dolloff. "At the habitat patch scale, which corresponds to where trout actually live, we’ve found that this correspondence varies in relation to elevation, aspect, riparian cover, and other local conditions."
With 250 watersheds in the Southern Appalachians instrumented and several hundred more sites established in the northeastern states, this project will provide managers with direct and precise information they can use to plan future habitat for brook trout across the East.
"We plan to use the relationship of air and water temperature along with knowledge of trout distribution and abundance across a variety of habitats to identify and rank the resiliency of southern mountain watersheds to climate change," says Dolloff. "This will give managers another tool to help prioritize locations to ensure the survival of brook trout and other coldwater species."
Transitions from Cold to Warm
For the USGS collaboration, Dolloff and partners are expanding their study into the very different environments of the Piedmont and the Coastal Plain, where a network of rivers and streams feed into the Albemarle-Pamlico Sound along the coasts of Virginia and North Carolina.
While the core data collections in the expanded study also emphasize temperature and landscape habitat attributes, the emphasis for this part of the project is more on the possible impacts of rising temperatures on relationships among temperature, water quality, aquatic communities, and ecosystem services to meet human demands.
"We don’t know yet if the relationships we found in coldwater streams can be extrapolated to cool or warmwater streams," says Dolloff. "We’ll collect data from paired thermographs located from the mountains down to the Coastal Plain. Then we’ll overlay that data with USGS data from the area to see if we can develop a similar means to identify habitats that will be particularly resilient under climate change."
Scientists from both agencies will assess specific stream conditions needed to support key fish species that rely on cold water and model the likelihood of the occurrence of those species in any given stream patch. With combined models, the project will define cold- and warmwater stream areas, homing in on the transitions from cold to warm water, and the resulting effects on fish communities. To test a range of climate change scenarios from 2000 to 2100, climate change projections will be integrated with the new combined stream models.
"The ultimate goal of this collaborative modeling effort is to provide tools managers and planners can use to look at how well different strategies will work under climate change and in relation to projected land use patterns," says Dolloff.
For more information: Andrew Dolloff at 540–231–4864 or adolloff@fs.fed.us
