Waters

UVA efforts that have received investments include the Karsh Institute of Democracy, neuroscience and brain research in Alzheimer’s disease and autism, the Environmental Institute, the Paul and Diane Manning Institute of Biotechnology, and initiatives in precision medicine and health and in digital technology and society.

“The University has made a powerful commitment to find real world solutions to climate change challenges,” said Karen McGlathery, director of the Environmental Institute. “At the Environmental Institute, we are excited about our expanded mission to bring researchers from many disciplines and community partners together to develop solutions that address the most pressing environmental challenges of our time. The work of the Environmental Institute connects research and action in ways that improve people’s lives.”

Philanthropic support for new faculty, postdoctoral positions, seed funding, and other elements of the University’s research infrastructure will advance these important efforts in essential ways and make a substantial difference in the progress UVA researchers make. These investments will help translate research into policy and practice.

When scientists pay attention to rivers, it’s in their nature to observe, measure, and analyze. Tassone (Grad Arts & Sciences '23), who received his doctorate in environmental sciences in May and was the Kenneth L. Bazzle Fellow with the Jefferson Scholars Foundation, studies the effects of temperature extremes on rivers and other bodies of water. In a journal paper titled “Increasing Heatwave Frequency in Streams and Rivers of the United States” published in the October 2022 Limnology and Oceanography Letters, Tassone provided the first assessment of heat waves in rivers for a large geographic area in the United States.

What Tassone discovered is that riverine heat waves are increasing in frequency and duration. It’s an area of research that, until now, was unexplored.

“Most of the work that’s been done on heat waves in water has been conducted in the ocean,” he explained. “That’s for a variety of reasons. You can use a satellite to get a lot of temperature data for the ocean. What’s been overlooked are heat waves in smaller bodies of water—ones that you can’t really collect data from with a satellite.”

Tassone began searching for data sets that used temperature sensors placed physically into bodies of water. He wanted those that were collecting information multiple times a day over the course of several years. “The United States Geological Survey does a lot of monitoring of water quality in streams and rivers throughout the U.S.,” he said. “One of the variables that they measure is water temperature. So, basically, I went through the USGS database and pulled out all the water temperatures for the past 26 years and looked for these heat waves.”

Riverine heat waves are classified as such only when they meet specific criteria. To qualify, two things need to happen. Observed water temperature must exceed a seasonally adjusted 90th percentile threshold, and the temperature must persist above this threshold for a period of at least five days.

“I pulled out all the highest-quality water temperature datasets that USGS had between 1996-2021, which resulted in 70 streams and rivers throughout the U.S. and performed this heat wave analysis on it,” he said. “And what I found was that much like we’re seeing in the atmosphere and in the open ocean, we’re finding that heat waves in rivers have significantly increased in frequency over the past two to three decades. Associated with that is a doubling of the number of heat wave days that you have in a given year.”

In addition, heat waves in rivers are significantly increasing in frequency in the summer and fall—though they can occur in winter and spring—and they relate to periods of low water discharge. Sites above dams also experience heat waves in increasing frequency.

Tassone’s findings have implications for public policy and waterway management in the future. As a result of his findings, he was asked to co-author a report for the Chesapeake Bay Program’s Science and Technical Advisory Committee on rising watershed and bay temperatures.

Left: In the Pace Lab at UVA, Tassone filters local water samples for suspended sediments.
Middle: Tassone discusses the results of a wavelet analysis with his Ph.D. advisor Michael Pace.
Bottom: Heat waves in rivers are increasing in frequency in summer and fall, especially during periods of low water discharge.

“There is public interest in these emergent disturbance events in riverine systems,” he said. “In the Chesapeake Bay region, we’re concerned about several different organisms, but probably the most vulnerable would be cold water organisms, like brook trout. They’re an essential part of headwater stream ecosystems and a highly prized recreational resource that bring in a lot of tax dollars. And they’re also an important part of the upper Chesapeake Bay watershed heritage.”

For fish like brook trout that require cold, highly oxygenated water, heat waves not only increase water temperature, but they also decrease the amount of oxygen—a double stressor for fish that have existed in Virginia mountain streams since the last Ice Age. Healthy watershed policies, such as establishing forested buffers, can slow the rate of rising temperatures, and increased monitoring of below normal stream flows can help with public awareness.

In recognition of his innovative research, Tassone was named the 2023 winner of the Bhakta Rath Research Award. The award, established in 2022 by a gift from Dr. Bhakta B. Rath and his wife, Sushama Rath, offers an opportunity to promote and reward excellence in public impact research for graduate or postdoctoral students and their collaborating UVA faculty member. The award recognizes scientists who conduct exceptional research in anticipation of the future needs of the nation. Tassone’s advisor was Michael Pace, W.W. Corcoran Professor of Natural History, in the Department of Environmental Sciences.

Tassone was a member of the Pace Ecosystem Ecology Lab, which focuses on freshwater and estuarine ecosystems, studying streams, rivers, lakes, and reservoirs to test ecological questions. The lab’s current research projects include resilience of ecosystems, algal blooms and the trajectory of aquatic ecosystems, dissolved organic matter, impacts on aquatic ecosystem processes, and freshwater salinization.

Now that he’s considered the question of riverine heat waves from a basic science perspective, Tassone is working to identify distributions and trends that predict where the heatwaves are most likely to occur. “From a private industry perspective, there are many things that water temperature impacts, like drinking water reservoirs,” he said. “There’s this worry that as things warm, there can be an increase in the frequency of harmful algae blooms. There’s also an impact on the distribution and toxicity of pollutants. And nuclear power plants that are located along a river to cool their turbines, if that water becomes hotter, it’s going to be less effective at cooling.”

Tassone accepted a postdoctoral fellowship at Michigan Technological University, where he continues his research. The campus is in Michigan’s Upper Peninsula on the Keweenaw Waterway, just a few miles from Lake Superior. He’s grateful for the award and the recognition he’s received for his watershed research. “It’s a nice recognition of the novelty of this work and both the basic and applied questions that it’s addressing or working towards addressing. It goes a long way with helping to provide justification for doing more of this type of work.”