Each summer, more and more lake beaches are forced to close due to toxic algae blooms. While climate change is often blamed, new research suggests a more complex story: climate interacts with human activities like agriculture and urban runoff, which funnel excess nutrients into the water. The study sheds light on why some lakes are more vulnerable than others and how climate and human impacts interact — offering clues to why the problem is getting worse.

Michigan State University researchers discovered key climate-related patterns in algal biomass levels through time for freshwater lakes. They used novel methods to create and analyze long-term datasets for thousands of lakes from open-access government resources and from satellite remote sensing. This research, published in Proceedings of the National Academy of Sciences, provides crucial insights into how climate affects lake ecosystems. 

The team studied chlorophyll levels, a measure of algal biomass, in lakes across the U.S. from the last 34 years. Climate change is thought to intensify lake algal blooms and increase the likelihood of “regime shifts,” or sudden and long-lasting changes in the structure and function of an ecosystem.

“Our research demonstrates that the relationship between climate change and algal biomass is more complex than expected,” said Patricia Soranno, a professor in the MSU College of Natural Science and one of the co-lead authors of this study. “While climate change is a significant driver in algal biomass, we found that the impacts are not always gradual or predictable. To effectively manage and protect lakes, we need to study these effects in many different local and regional contexts.”