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News — DALLAS () – An international team of winter lake researchers provides a simple answer to a profound question in a new synthesis study published in the journal : “Yes, it matters that lakes are losing ice.”

At least 1.1 billion people live in areas near lakes that experience winter ice cover. Over the past 165 years ice duration has decreased and thousands of lakes that historically froze every winter now experience ice-free years. Not only do these changes have socioeconomic consequences for nearby communities, the study finds, but the quality and duration of that ice cover also controls key physical, chemical and biological processes within freshwater ecosystems.

“Although interest in winter research has increased, ice on lakes during winter is not well studied,” said Xiao Yang, a remote sensing hydrologist at SMU. “In comparison, research done during warmer months, or what we call open water months, is more common even though how the winter season impacts lakes is just as important as the summertime.”

Broad Consequences

Decreasing lake ice coverage and the resulting warmer water temperatures have these impacts:

• Changes in lake water quality: Algae blooms are linked to warmer temperatures, longer summers and nutrient overloads. Stagnant water also lets algae flourish and produce cyanotoxins, a compound that is harmful to human and wildlife health. Ice cover has been shown to have a complex or even opposing effect on the development of algae blooms.
  
  
• Threats to native biodiversity and potential for species invasion: Declines in native biodiversity have reached a crisis level in freshwater ecosystems. Lake ice creates a distinctive ecological niche space. Ice-associated organisms provide important food sources for higher-trophic level organisms, not only during winter but also during spring ice melts. Additionally, some wildlife use lake ice during critical life stages such as reproduction or migration.

• Increases in carbon retention: Ice cover separates lakes from the atmosphere, preventing a gas exchange during winter. Previous research suggests that ice cover increases carbon retention and that lakes with longer ice duration tend to stay cooler year-round. The study’s authors theorize that cooler lakes with longer ice cover have lower annual nitrous oxide emissions, another potent greenhouse gas.
  
  
• Increased chances of heavy precipitation events: Lake-effect snow is only possible over open water. Once the lake freezes, evaporation is limited and precipitation decreases. Research simulations have found complete freezing of the Great Lakes reduced snowfall by 84 percent and decreased cloudiness, temperature and near-surface wind speeds. With rising temperatures, the forecasted loss of lake ice has the potential to substantially change winter climate downward of the Great Lakes.
  
  
• Threats to winter fisheries: Fish residing in seasonally ice-covered lakes can be important culturally, economically and as a food source for many people with harvest rates of some species being higher during winter compared with ice-free periods. Access to fish during winter months hinges on ice cover and the nutritional quality of fish could also decrease with warmer temperatures.
  
  
• Human use of lakes: Winter lake ice supports human activities tied to recreation, spiritual connections, aesthetic appreciation, cultural identity and ice roads for winter transportation. Recent models forecast changes that will reduce the reliability of ice coverage for human uses.

Massive Shifts Due to Lake Ice Loss

Yang’s expertise is in using NASA satellite images to monitor rivers and lakes around the world and how they are changing in response to climate change and other human influences. He leads the Remote Sensing of Hydrology and Limnology Lab at SMU.

One of the analyses conducted for the synthesis study estimated how many people live around lakes that are currently seasonally ice covered. While researchers have population data globally, gathering ice information at that scale goes beyond on-the-ground monitoring capacity. Yang’s lab assisted with gathering ice cover information from images captured by the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite for the duration of the past two decades.

“We need to understand how ice impacts the ecosystems of lakes before it goes away,” he said. “Lakes losing ice is going to cause massive shifts in lake ecosystems in ways we don’t fully comprehend. In order to adapt, it’s crucial for us to understand what’s at risk for being lost.”

The research team includes experts from the United States, Canada and Sweden. Co-authors are Stephanie Hampton and Ryan McClure of Carnegie Institute for Science, Stephen Powers of Baylor University, Hilary Dugan of the University of Wisconsin, Lesley Knoll of Miami University of Ohio, Bailey McMeans of the University of Toronto, Michael Meyer of the U.S. Geological Survey, Catherine O’Reilly of Illinois State University, Ted Ozersky of the University of Minnesota, Sapna Sharma of York University, David  Barrett of the University of Calgary, Sudeep Chandra of the University of Nevada, Joachim Jansen and Gesa Weyhenmeyer of Uppsala University, Milla Rautio of the Université du Québec, and SMU’s Yang.

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