Winters on the North American Great Lakes historically have been long and harsh — conditions that make it difficult to collect water samples during the coldest months of the year. Filling this data gap could provide crucial information to managers about nutrient cycles, food webs, climate change, and other factors affecting Great Lakes resources and communities.
Thanks to funding from Michigan Sea Grant, Tristy Vick-Majors at Michigan Tech University has been working to coordinate “winter grabs” of these hard-to-get water samples. In February 2025, multiple groups of researchers across all five Great Lakes ventured onto the ice to retrieve frigid samples. Michigan Sea Grant director Silvia Newell and her lab joined a sampling effort with Nicole Wagner and students from Oakland University to collect samples from beneath Lake St. Clair’s ice near Detroit.
Scientists are gathering this data to help improve understanding of the connection between seasonal processes in the lakes and ecology and health of their ecosystems. The results of this research will help scientists and managers understand productivity and under-ice conditions in the Great Lakes during winter, which can impact fisheries, spring blooms that form the basis of food webs, and potentially summer harmful algal blooms.
Ice Cover and Productivity
Winter on the Great Lakes extends for more than one-third of the year, approximately 3-6 months, yet historically, scientists have collected less data during this period due to the danger and logistical difficulty of sampling on ice. As climates change, lakes are undergoing shorter cold periods during winter, which is reducing ice cover and increasing air temperatures and precipitation. Recent research has found that, on average, the Great Lakes are experiencing a loss of 14 winter days per decade for the period 1995–2023. As a result, winter limnology represents a major gap in understanding of how the lakes are responding to a changing climate. Winter data is critical to understand the impact on some commercially important fish species such as whitefish, which lay their eggs in winter under ice cover.
Research from polar regions and smaller temperate lakes has also shown that significant productivity occurs during winter. As ice cover decreases, the transmission of light through water changes, impacting nutrient availability and phytoplankton productivity. Phytoplankton is crucial because it is the primary producer in the food chain of the lakes, serving as the base of the food web for many aquatic organisms, including zooplankton and small fish, which are then eaten by larger predators. Ice cover and temperature also affect bacterial communities that play a crucial role in nutrient cycling. Ultimately, these changes can alter processes, such as lake thermal structure (layers of water of different temperatures), and affect water quality, productivity, and biodiversity in the lakes.
Nutrient Cycling
Dr. Newell is also co-leading a complementary, National Science Foundation-funded research project with Dr. Jenan Kharbush (University of Michigan) and Dr. Chris Ward (Bowling Green State University) that is gathering data to understand how nitrogen cycling in winter impacts nutrients and phytoplankton communities in large, temperate water bodies. In this project, the team is using Lake Erie as a case study because it is one of the most socioeconomically important resources in the United States, providing drinking water, recreation, and fisheries on which millions of people depend.
Recent work suggests that during winter, under-ice nitrogen cycling processes, such as nitrification, are important in determining the types of nitrogen that are produced and available for spring phytoplankton blooms. These spring blooms directly support healthy fisheries by producing the DHAAs and omega-3 fatty acids that are important to peoples’ health. In the last few decades, winter, spring, and summer phytoplankton communities in Lake Erie have changed significantly due to several factors, including invasive species, warming waters, and cultural eutrophication. The research team will gather data to improve understanding of winter nitrogen cycling to help determine how changes are affecting phytoplankton and, consequently, food web and fisheries.
Winter conditions affect physical, biogeochemical, and biological processes, not only during winter but during the rest of the year as well. Ice cover in particular affects many aspects of these large, dynamic ecosystems, and changes in its extent and duration are altering key lake processes. The Great Lakes comprise the world’s largest freshwater ecosystem, providing fresh drinking water and diverse ecosystem services to millions of people. As a result, winter limnology represents a key knowledge gap that limits understanding and protecting the Great Lakes and its ecosystems.
