Session 10: Maine Lake Resilience and Response to Regional and Climate Stressors

Please reach out to individual speakers if you are interested in viewing PowerPoint presentations from this session. Due to limited staffing, we are unable to post the presentations to the website.

Afternoon Session – 1:30PM-4:00PM
Cumberland Room, First Floor

  • Drinking Water Operators: Two Training Contact Hours (TCH) are available for this session from the Maine CDC  Drinking Water Program. Sign-up sheets are located in the session room.

Session Co-chairs
Linda Bacon, Maine Department of Environmental Protection
Rachel Hovel, University of Maine-Farmington
Sarah Nelson, Appalachian Mountain Club

Maine lakes are susceptible to regional and local stressors, including climate change, point-source and atmospheric deposition of pollutants, and land use changes. In response, lakes have exhibited shifts in physical and biological conditions, creating challenges for supporting lake resilience at levels from the individual lake to the landscape. Emerging patterns include shifts in phenology, geochemistry, and lake productivity, and associated challenges include evaluating cyanotoxin hazards, emerging contaminants, and economics of water clarity. Variation in response and resilience across lakes highlights the importance of comprehensive research and monitoring in developing a landscape-wide perspective on lake ecosystem change. This session will allow researchers and lake watershed managers to share recent work, especially related to evaluating regional and local drivers across a range of lake types.

Session Schedule


Adaptation to Elevated Sea Salt Levels in Sewall Pond

Mary Rogalski (1), Owen Chambers (2), Sophie Burchell (2), Brady Nichols (2), Kayla Kulzy (2)

  1. Biology and Environmental Studies, Bowdoin College 
  2. Bowdoin College

Maine lakes tend to be ion-poor due to the regional geology, but those near the coast may receive added salt from sea spray or tidal influence. Sewall Pond in Arrowsic, ME is one of the highest salinity lakes regularly monitored by the Maine Department of Environmental Protection (DEP). Data collected by DEP, volunteer monitors, and our lab indicate that salt levels have increased in Sewall Pond after the outflow culvert was modified in 2014 to improve migratory alewife passage. In fall of 2022, Sewell Pond reached a conductivity of 1080 uS/cm, after fluctuating between around 200-600 uS/cm the previous several years and staying around 150-250 uS/cm between 1980-2013. How do these changing salinity conditions affect resident organisms? Experiments working with Daphnia, microscopic crustaceans living in lakes and ponds, show that Sewall Pond water is supportive of their growth and reproduction, even for populations from relatively low ion lakes; however, the high salinity conditions observed in October 2022 were stressful for Daphnia from the low-ion lakes. Interestingly, Daphnia collected from Sewall Pond during high salt conditions appear to be better adapted to handle this salt toxicity relative to those collected during a lower salinity time period. This supports that Daphnia in Maine lakes can adapt to their local lake water chemistry; conditions that might exert stress, such as very low or high salt conditions, may be less stressful or even beneficial for resident populations. Evolution may even be happening from one year to the next!


Shifting Seasonality: Consequences of the Changing Autumn Season for Maine’s Ecologically and Recreationally Valuable Mountain Ponds

Amanda Gavin (1) (student), Jasmine Saros (1,2,3), Sean Birkel (2), Julia Daly (4), Rachel Hovel (4), Sarah Nelson (5)

  1. University of Maine Ecology and Environmental Sciences 
  2. University of Maine Climate Change Institute
  3. University of Maine School of Biology and Ecology
  4. University of Maine Farmington
  5. Appalachian Mountain Club

Mountain ponds are susceptible to regional and global environmental change and are recreational hotspots that contribute to Maine’s tourism economy; however, the impact of climate change on the water quality and recreational value of these ponds remain unclear. In Maine’s mountain region, the most notable warming trends have occurred in the winter and fall. Warming in these seasons could affect two key physical processes that influence lake ecology: ice-on and water column mixing. This project focuses on nine mountain ponds in Maine that are representative of important high-elevation habitats and are recreationally significant, as they provide critical water sources for hikers and are backcountry fishing destinations. The conservation status of these ponds varies from no current protections to protection of the full watershed within conserved mountain ranges or ecological reserves. The goal of this project is to identify trends in autumn mixing and ice-on, inferred through long-term temperature monitoring and a new community science initiative, and integrate these results with a gap analysis of conservation status across mountain pond watersheds to identify how conservation interacts with climate change impacts in mountain ecosystems. We will present results from mixing and ice-on trends analyses, community science ice-on observations, and the conservation gap analysis. Together, the interdisciplinary nature of this research quantifies mountain lake vulnerability to climate change and applies these results to identified conservation gaps to develop a solution-oriented framework for future mountain pond management.


The Distribution of Toxic Planktothrix Strains Across Maine

Robin Sleith (1), Linda Bacon (2), Peter Countway (3)

  1. Bigelow Laboratory for Ocean Sciences 
  2. Maine Department of Environmental Protection
  3. Bigelow Laboratory for Ocean Sciences

Climate change and nutrient pollution in freshwater ecosystems have led to the increase in frequency of harmful cyanobacterial blooms. These blooms can contain toxic and/or non-toxic strains of cyanobacteria. Planktothrix is one of the more common cyanobacteria causing blooms in Maine. In this study we survey 50 Maine lakes to determine the distribution of toxic and non-toxic strains of Planktothrix across the state. We find multiple strains occurring in some water bodies, while others contain only a single strain. This information, combined with historical data, will help to determine the factors responsible for toxic strains occurring or dominating in lakes across Maine.


Assessing Need and Feasibility of Bacterial Monitoring at Freshwater Beaches in Maine

Margo Kenyon (1) (student), Susan Gallo (2), Meagan Sims (3), Tristan Taber (4), Linda Bacon (3)

  1. Colby College
  2. Maine Lakes
  3. Maine Department Environmental Protection
  4. Lake Stewards of Maine

Maine’s climate, with infrequent periods of prolonged heat, historically kept our lakes, rivers, and streams cool and refreshing during the hot summer months. Today, warmer water in our lakes and ponds can create conditions that allow more harmful pathogens to persist and multiply. That threat is poised to grow in the future as the climate warms and as more residents and visitors seek out local freshwater swimming areas to escape the growing heat. More people crowding into small, still freshwater swim locations has the potential to increase the prevalence of disease-causing pathogens in the water and threaten public health. A recent project by Maine Lakes, Lake Stewards of Maine, and the Maine Department of Environmental Protection investigated the feasibility of and interest in developing a bacteria monitoring program for freshwater swim areas. Project staff surveyed stakeholders to gauge awareness of and interest in bacterial monitoring programs, and built an extensive database of freshwater swim areas in Maine including ownership, size, and other features relevant to potential monitoring activities. These criteria were then examined using environmental justice criteria to help identify priority focus areas for a potential bacterial monitoring program. Results of this important investigative effort will be shared and underscore the interest in, need for, and challenges ahead for a statewide freshwater bacteria monitoring program in Maine.


Afternoon Break (Auditorium)


Building Resilience in Acadia National Park’s Lakes: A 45-Year Journey

William Gawley (1), Rachel Fowler (2), Kathleen Brown (1)

  1. National Park Service, Acadia National Park
  2. University of Maine

Acadia National Park has long been a valued site for monitoring and research studies to determine the effects of acid deposition, mercury contamination, nutrient enrichment, climate change, human impacts, and other stressors on the parks iconic and largely pristine lakes. A data history of nearly 45 years provides a provides a unique opportunity for park managers to have detailed information needed to directly address water quality management issues, such as risk assessment and mitigation of Harmful Algal Blooms (HABs). Many threats, including air pollution and climate change, are less manageable at the local level, but park studies contribute to the greater body of scientific and outreach efforts working to address these problems at the national and global level. All these accomplishments were made possible through long-standing and ongoing collaborations with federal, state, local, and academic partners. We continue to build on this strong foundation as we develop solutions to manage increasing environmental challenges to park water resources.


Impacts of Intense and Above-Normal Summer Precipitation on Lake Conditions and Trends

Ben Peierls, Maggie Welch
Lakes Environmental Association

One impact of climate change predicted for Maine is an increase in precipitation and precipitation intensity. Increased precipitation has the potential to affect lake trophic state through increased nutrient, organic matter, and sediment loading, depending on lake and watershed characteristics. High rainfall rates may have an even greater impact through significant watershed erosion. Parts of Maine experienced frequent and often intense rain events during 2023 making it the second wettest summer on record. Forty-one lakes in the greater Bridgton area were monitored biweekly or once seasonally for water clarity, total phosphorus, chlorophyll, and color. The impact from the excessive precipitation was visually apparent to monitoring staff (and the public) with water clarity generally lower and water color generally higher than long-term (up to 27 years) averages. Total phosphorus concentrations were also higher than average, but chlorophyll a concentrations varied little from long-term averages. These patterns were not always observed in lakes sampled one time during the summer, possibly because the visits were during a period of less rain. Despite the dramatic changes in water quality, the 2023 season caused little change to long-term trends. The observed conditions suggest that the intense precipitation caused high organic matter and total phosphorus loading, but did not lead to increased algal productivity during the season. The lack of productivity increase could be explained by lower light availability, no change in available phosphorus, increased flushing rate, or some combination of factors.


Valuing the Economic Benefits of Maine’s Lakes and Great Ponds in the 21st Century

Jianheng Zhao (1), Adam Daigneault (2), Keith S. Evans (3), Susan Gallo (4), Linda Bacon (5), Melissa Genoter (6)

  1. Center for Research on Sustainable Forests, University of Maine
  2. School of Forest Resources, University of Maine
  3. School of Economics, University of Maine
  4. Maine Lakes 
  5. Maine Dept. of Environmental Protection 
  6. Ecology and Environmental Sciences, University of Maine

Over the past 25 years, the 2,700 Great Lakes and Ponds of Maine have faced challenges such as development, invasive species, and climate change, prompting a reassessment of their economic value to guide conservation efforts effectively. This study uses a range of methodologies such as travel cost modeling, expenditure analysis, surveys, and hedonic price analysis to conduct a comprehensive assessment focused on recreation, water consumption, youth camps, and the impact of water quality on property values. We estimated that the total net economic value of Maine’s Lakes is nearly $14 billion, a 15% increase over the previous study, with the largest contribution coming from lakefront properties. We also found that property owners place a premium on improved water quality: a one-meter increase in water clarity correlates with a 6.6% increase in property values, averaging $3,824 per property. Across all of Maine’s lakes, a 1% improvement in water quality is estimated to add $15 million to the value for property owners. An accompanying survey on perceptions of lake water quality emphasizes the importance of water clarity in recreation choices, with the average visitor indicating lake quality at a level more than safe for swimming. Our study emphasizes the need for sustainable management of Maine’s water bodies, considering ecological, social, and economic factors. The findings offer significant evidence for policymakers to include lake water quality values in environmental decision-making processes.

About the Session Chairs

Linda Bacon fell in love with lakes at a young age and grew to appreciate the ecology of aquatic systems in college and grad school.  After finishing her MS coursework, Linda worked on acid rain projects at the University of Maine for five years before joining Maine DEP’s Lake group in 1989, working her way up to Lake Assessment Section Leader.  Her interests include plankton dynamics, mercury contamination, cyanotoxins, effects of climate change, as well as paddling a canoe on a quiet lake early in the morning.  For Linda, limnology is an avocation as well as an occupation. 

Rachel Hovel is an aquatic ecologist who studies fishes and invertebrates across a range of freshwater habitats, and Associate Professor of Biology at University of Maine-Farmington. Major themes of her research include the timing of ecological events and diversity in life histories and habitats. In particular, she is interested in how changes to freshwater environments–especially climate change–influence aquatic organisms and ecosystems. She is a co-PI on the Maine Mountain Ponds project, which investigates lake ecosystem response to climatic change across an elevation gradient. 

Sarah Nelson is the Director of Research at the Appalachian Mountain Club. Her research focuses on understanding the effects of atmospheric pollution and climate change on forests, foodwebs, and freshwaters in remote and protected ecosystems. Current research includes geochemistry in lakes, climate change with a focus on changing winters, and mercury contamination, using approaches including long-term monitoring, biosentinels, and citizen/community science. Research sites include remote or protected lands, including long-term sites across Maine, mountain ponds in the Northeast, and national parks around the U.S.