Changing Waters: 

Clint Muhlfeld on Aquatic Integrity

USGS researcher Clint Muhlfeld already has a long history in the waters of the Crown. But these days, as an aquatic biologist, all of his research is pointing more and more to the impacts of climate change, whether he’s looking at fish, entire stream reaches, algae blooms, or a rare glacial stonefly. Together, these four projects give us a fuller picture of how the Crown’s changing climate is affecting its lakes, rivers, and glaciers. They also point to how we can address these impacts to protect the cold, clear waters of the Crown, and the species that live in those waters.

Little bugs, big changes

High in the glaciers and glacial streams of Waterton-Glacier International Peace Park lives the humble meltwater stonefly (scientific name, Lednia tumana or L. tumana). Humble no more, though, as Dr. Muhlfeld and his research associates have discovered its importance as an early-warning sign for climate impacts in mountain ecosystems and the Crown. It’s also a candidate to be listed as an endangered species. L. tumana is found only in the glacial and snowmelt streams of the Crown’s highest mountains, within 500 meters of a glacier’s edge, a permanent snowfield, or a spring. It relies on icy cold water to survive.

Dr. Muhlfeld’s research and models suggest that climate change threatens L. tumana’s cold water habitats and, as a result, the species itself as we lose glaciers and snowfields in the high country. And, while only time will tell whether we can save L. tumana, what we’ve learned from this humble little stonefly may help us take action to lessen the impacts on other aquatic species we care about.

Learning to predict stream temperatures

This project combines data collected from more than 300 stream sites with sophisticated modeling techniques to look at how streams and aquatic species may change in the coming decades. Researchers are looking at rising temperatures, disturbance events (like floods, fires, and ice scouring), and the changing water cycle to determine which streams in the Crown might be most at risk from the impacts of climate change. These models will help us understand where it could get too hot for certain fish and other aquatic species in the future (see map of bull trout habitat, below), so that we can focus our attention and conservation work on these places.


Map.  Model of critical bull trout habitats in the year 2059. Red indicates those reaches of stream that, without restoration efforts, are likely to be too warm to continue to serve as bull trout habitat in the future. 

Using genetic studies to find and restore the Crown’s most threatened streams and fish

Fish need to move to survive as both individuals and populations. They need connected waterways to spawn, raise their young, and feed. Using what is already known about fish behavior and needs in the Crown’s rivers and streams, Dr. Muhlfeld and his colleagues have developed new methods that tracks how individual fish move as a function of water temperature, flow, habitat type, physical barriers (like stream culverts) and other factors.

This new approach allows researchers and manag­ers to assess the impacts of things like cli­mate change, invasive species, and habitat loss on the genetic diversity, numbers, and distribution of fish popu­lations through time. Altogether, this work will help produce vulnerability maps that can be used to develop priorities for on-the-ground restoration efforts that will help protect the most threatened stream segments and fish populations in the Crown as temperatures continue to warm.

Blooming algae, warming streams

If you thought being a stonefly was humble, consider Didymosphenia geminata (“didymo” for short). It’s a freshwater alga native to North America that’s recently spread south to warmer waters, and has been showing up more and more in the Crown these days. In other places it’s occurred, didymo has been shown to disrupt food webs by changing the makeup of invertebrate communities – for example, more snails, midges, and caddisflies, but fewer mayflies. Large mats of didymo covering stream beds can even alter stream flows and water pH levels, not to mention gumming up boating and fishing gear.

Researchers have been searching for the causes of didymo blooms. Using stream temperature data from Glacier National Park and the US Geological Survey, they’ve discovered that where summer stream temperatures are rising, didymo tends to follow. 

As a result, we can now consider a bloom of didymo as one early warning sign that a stream in the Crown is getting warmer. And, as temperatures are expected to rise even further, we’re likely to see didymo more frequently, in more places.


Photo: didymo colonized by blackfly larvae.