Using paleolimnology and eDNA to assess links between warmer winters and summer blue-green algae in Maine lakes

Institution: University of Maine
Sponsor: Water Resources Research Institute National Competitive Grants Program (104g)

Research Team:

  • Team Leader: , associate director, Climate Change Institute; professor of paleolimnology and lake ecology, School of Biology and Ecology, 91¸£Àû
  • , professor of evolutionary applications, School of Biology and Ecology, 91¸£Àû
  • Charlie Culbertson, U.S. Geological Survey
  • , Bigelow Laboratory for Ocean Sciences
  • , Colby College

Project Partners:

  • Maine Department of Environmental Protection (DEP)
  • Lakes Environmental Association
  • Portland Water District
View of Sebago Lake, Maine, at water level with ducks and mountains in background
Sebago Lake State Park, Maine. Photo: photophil321/Shutterstock

Project Summary

Blooms of cyanobacteria, or blue-green algae, are a growing problem in freshwater bodies across the United States, where they produce toxins that can cause illness in humans and other animals as well as environmental harm.

The ecological factors that promote the development of these harmful algal blooms (known as cyanoHABs) are poorly understood, and considerable uncertainty remains about how climate interacts with other drivers in determining the prevalence of cyanoHABs.

The main toxin of concern in the northeastern U.S., and in Maine, is microcystin-LR, which is produced by different groups of cyanobacteria found in lakes with low to high nutrient levels, indicating the widespread nature of this threat. The toxin is found in lakes across Maine.

A key question that this project will address is how warming winters may affect the increasing frequency of cyanoHABs in Maine’s lakes. This is a pressing question, as winter is the fastest changing season in Maine, with a rate of warming twice that of summer. All three of Maine’s climate divisions (Northern, Interior and Coastal) are warming more in winter than in summer, with the greatest change in the Coastal division.

Researchers will use paleolimnology, the study of lake sediments to reconstruct past environments, to determine how warmer winters over the past 125 years have affected the occurrence of toxin-producing cyanobacteria in Maine lakes. The research will leverage newly developed capacity in environmental DNA (eDNA), including sediment DNA (sedDNA), from the NSF-funded Maine EPSCoR RII Track 1 eDNA project. Members of the research team are also involved with the eDNA project.

Knowledge of whether cyanoHABs respond to warmer winters will help lake management agencies (federal, state, municipal and nonprofit) to better anticipate toxic blooms based on winter conditions and modify management plans as needed.

Project Update

To better understand the environmental conditions that favor cyanobacterial proliferation, there is a need for taxon-specific research on high-priority cyanobacterial taxa over longer timescales that are focused on specific and relevant metrics of climate variability. This research thus directly answers this knowledge gap by investigating the impacts of warmer winters on Gloeotrichia populations in Maine lakes over the past 125 years. To date, this research has collected sediment cores from 12 lakes across the state of Maine that vary in trophic state and climate zone. A suite of analyses on the sediment cores, including water content analysis, photosynthetic pigments, sedDNA, and sediment dating have been completed. Long-term average temperature records for each climate zone (Northern, Interior, Coastal) are available from National Climate Data Center records and when needed, are supplemented with data from the Climate Reanalyzer (Climate Change Institute, University of Maine). Initial findings suggest that cyanobacterial community abundance and composition, including different taxa of potentially harmful cyanobacteria are different between lakes of various trophic states. Furthermore, Maine lakes with long-term nutrient inputs (sustained nutrient presses from phosphorus-rich underlying geology) are more sensitive to increases in winter minimum temperatures. Increases in winter minimum temperatures can have impacts on physical lake qualities like earlier ice out and earlier/longer spring mixing that affect nutrient replenishment and plankton succession. Additionally, in the absence of long-term P-inputs (e.g. P-inputs from underlying geology), regardless of contemporary trophic status, lakes in the northern region of Maine are more sensitive to increases in summer maximum temperatures. Increases in summer maximum temperatures can promote cyanobacteria both directly (e.g., higher temperature optima, higher growth rate at a larger temperature range) and indirectly (e.g., longer and/or stronger stratification).

These results will inform lake managers about whether winter climate conditions are important in driving cyanobacteria, and especially Gloeotrichia blooms, and if so, will aid in developing forecasting systems prior to summer blooms. With the knowledge of whether cyanoHABs respond to warmer winters, managers can better anticipate summer conditions based on current winter conditions to modify management plans as needed. As state, municipal, and non-profit lake management agencies are increasingly faced with the management of cyanoHABs, specifically Gloeotrichia blooms and microcystin concentrations, insight into conditions that favor cyanoHABs will foster protection and maintenance of safe waterbodies in Maine in the future.

To better understand the effects of long-term seasonal warming on cyanobacteria in Maine lakes, the lack of studies focused on oligotrophic lakes is a challenge that needs to be addressed. While there is a massive body of previous work focused on cyanobacterial ecology in eutrophic and hypereutrophic systems, much less is understood in oligotrophic (i.e. low-nutrient) lakes, though cyanobacteria do exist and bloom in these systems as well. There is widespread evidence of cyanoHABs of various genera in oligotrophic lakes, but given the paucity of documentation, cyanoHAB controls in oligotrophic lakes are inconclusive or contrary. There is growing concern about cyanoHABs in oligotrophic lakes as they are often used for recreation and drinking water, especially within the context of the possible economic and toxicological effects of cyanotoxins. This is of utmost concern in the state of Maine, in which the clear majority of lakes in Maine are oligo- or mesotrophic. In Maine, there are more than 40 surface freshwater sources used for drinking water, and 10 of these are not filtered as part of the treatment process. Given the occurrence of cyanoHABs, particularly Gloeotrichia, in lakes across trophic states and the reliance on oligotrophic lakes in Maine for drinking water, understanding of mechanism promoting blooms is urgently needed. Of the lakes included in this proposed work, 50% (6/12) of the lakes are classified as oligotrophic systems. Continuing to include low-nutrient systems in future studies that seek to disentangle the drivers of cyanobacterial proliferation is necessary to accurately determine the risk of microcystin production in oligotrophic lakes used for recreation and drinking water.

Stakeholders in the state of Maine have been integral in efforts to collect sediment cores from the twelve lakes included in this study. From individual landowners to local lake associations, state-wide nonprofit organizations, the Maine Department of Environmental Protection, and indigenous people groups, engagement with Maine stakeholders was mutually beneficial. Not only was the research group able to gain access to the study lakes, but stakeholders were able to converse, learn, and collaborate with the researchers. This grant positions the researchers to further collaborate with the stakeholders mentioned above, especially larger lake-focused nonprofits and research centers like the Lakes Environmental Association, Lake Stewards of Maine, Lakes of Maine, the Midcoast Conservancy, and the 30 Mile River Watershed that have been already been involved in this research, to date. In addition to scientific partnerships and collaborations, the results of this research are directly applicable to individual stakeholders also served by these groups; these partnerships can be used to effectively disseminate results to municipal, non-profit, and individual stakeholders.

Resources:

Products

Presentations

  • Avery Lamb, Robin Sleith, Pete Countway, Suzanne McGowan, Andrew Rominger, Michael Kinnison, and Jasmine Saros. Do all cyanobacteria win? Using paleolimnological approaches to disentangle the long-term nutrient and climate drivers of harmful cyanobacteria blooms. Association for the Sciences of Limnology and Oceanography (ASLO). March 2025. Charlotte, NC.
  • Avery Lamb and Jasmine Saros. Using paleolimnological approaches to disentangle the long-term nutrient and climate drivers of harmful cyanobacteria blooms. University of Maine Climate Change Institute Borns Symposium. April 2025. Orono, ME.
  • J.E. Saros. Using Paleolimnology and SedDNA to Evaluate the Links Between Warmer Winters and CyanoHABs in Maine Lakes. Joint Aquatic Sciences Meeting (JASM)
  • Avery Lamb. Using Paleolimnological Tools to Evaluate the Links Between Climate Change and CyanoHABs in Maine Lakes. University of Maine Student Symposium. April 2022. Awarded Best Graduate Presentation in Natural Sciences

Awards/Achievements

  • University of Maine Graduate Student Government Grant awarded to Avery Lamb to support grant-related laboratory expenses. September 2024.
  • University of Maine Graduate Student Government Grant awarded to Avery Lamb to attend the Association for the Sciences of Limnology and Oceanography (ALSO). March 2025.
  • Avery Lamb, Jasmine Saros. Maine Center for Genetics in the Environment Graduate Student Grant.