Session 6 – Maine Lakes: Climate Change Impacts and Adaptations

Two Training Contact Hours are available for this session from the Maine CDC Drinking Water Program. Participants interested in applying should email

Wednesday, March 31, 1:30PM-3:30PM

Amanda Gavin, FB Environmental
Margaret Mills, FB Environmental
Rachel Hovel, University of Maine, Farmington
Ben Peierls, Lakes Environmental Association

Lakes are often considered sentinel ecosystems, in that they respond rapidly to regional environmental change. As the lowest point in the catchment, lakes integrate inputs from the surrounding watershed, so changes in lake biological and physical properties act as “canaries in the coal mine” and reflect changes occurring in the climate, atmosphere, and surrounding terrestrial ecosystems. Ongoing research has demonstrated that Maine lakes are experiencing climate change through changes in water temperature and clarity, duration of ice cover, invasive plant populations, algal blooms, zooplankton composition, and more. This session invites talks that creatively address how Maine lakes are responding to climate change, what makes lake ecosystems less resilient to climate change, and what adaptations, both natural and anthropogenic, can mitigate impacts of climate change.

Session Overview


Maine mountain ponds reveal linkages among thermal, geochemical, and biological characteristics in the context of the Northeast’s recovery from atmospheric deposition and climate change

Sarah Nelson1, Julia Daly2, Rachel Hovel2, Amanda Gavin3, Stephanie Dykema4,5, William McDowell6
1. Appalachian Mountain Club, Gorham, NH
2. University of Maine-Farmington, Farmington, ME
3. FB Environmental, Portland, ME
4. University of Maine, Program in Ecology and Environmental Sciences, Orono
5. Niwot Ridge LTER, INSTAAR, University of Colorado, Boulder, CO
6. University of New Hampshire, Natural Resources & the Environment, Durham, NH

Mountain ponds in the northeastern US have undergone acidification and subsequent recovery due to changes in atmospheric deposition, and now additionally reflect physical and biological responses to climate change. These ponds are distinct from other lakes and ponds in the region as they are higher in elevation, generally forested, and have little direct impact from human land use in their watersheds. They are relatively small and could be vulnerable to the increases in extreme weather events, overall warming, and shortening of winter that are occurring throughout the northeastern US. We compiled data for mountain ponds >560 meters elevation and <60 ha surface area across the northeastern US (Northern Appalachians and Adirondack Mountains) spanning 1978-2019, with more detailed data for a subset of Maine Mountain Ponds in the Western Mountains region. The full, regional dataset includes 257 ponds, with strong and widespread significant declining trends in sulfate (95% of sites, ~45% decline) and increasing ANC at 53% of sites. Dissolved organic carbon (DOC) increased in 54% of ponds. Increasing DOC has been attributed to both changing sulfate and climate, specifically related to increases in precipitation and air temperature. Although these lakes are typically colder and experience more persistent winter snowpack than lower elevation lakes, their thermal structure is sensitive to warming air temperatures, which impacts water temperature, stratification, and ice duration. We studied a subset of mountain ponds in Maine to link these thermal properties with geochemical patterns and zooplankton communities. At these locations, increased DOC is associated with later onset of summer stratification and increased mixing following ice out. Increased DOC was also correlated with declining in situ total chlorophyll, suggesting either that light limitation is a likely mechanism regulating primary production in these mountain ponds or may point to the role of other factors correlated with DOC. These findings suggest 1) the need for integrated monitoring that collects data to evaluate connections between chemical, physical, and biological processes within mountain lakes, and 2) the value that the mountain ponds dataset provides for documenting decadal-scale trends. As questions of climate thresholds, cold refugia, and range shifts gain much-needed attention, we argue that these ponds provide the ideal setting for research in a rapidly changing ecoregion.

Lake phenology and climate change: zooplankton responses to shifting seasons in remote Maine lakes

Stephanie Dykema1,2, Sarah Nelson3, Ivan Fernandez2, Rachel Hovel4, Jasmine Saros5
1 Ecology and Environmental Sciences, University of Maine, Orono, ME
2 School of Forest Resources, University of Maine, Orono, ME
3 Appalachian Mountain Club
4 Department of Biology, University of Maine-Farmington, Farmington, ME
5 School of Biology and Ecology, University of Maine, Orono, ME

A video of this presentation is available

Climate change is influencing the timing of seasonally reoccurring events in ecosystems across the globe. Shifts have already been detected in northeastern lakes including earlier ice breakup and longer periods of thermal stratification. For many organisms, phenology is driven by temperature cues but for others, shifts in day length, availability of nutrients, or other seasonal cues are more important drivers. Even among those that depend on temperature cues, individual species respond at different rates depending on their life history traits and such asynchronies can result in a reorganization of ecological communities. Zooplankton, primary consumers in lentic food webs, react quickly to change due to their relatively short life cycles. Variability among different species’ responses to geochemical or physical shifts has resulted in measurable shifts in lake community structure. This research aims to understand how zooplankton communities, in lakes across the extremes of elevations and climate zones in Maine, respond to lake phenology. Zooplankton, chlorophyll-a, and water chemistry was measured under ice in winter, repeatedly over the course of spring warming, and during summer stratification and fall mixing in eight remote lakes. A chain of thermistors measured temperature in the epilimnion and hypolimnion throughout the year. We are comparing zooplankton phenology and community structure among seasons and among lakes to understand how variation in physical lake phenology influences the phenology of different plankton species. Interpreting the drivers of phenological shifts among lake ecosystem members will be imperative for understanding and predicting the complex effects of climate change on freshwater systems.

Is Maine’s Climate Changing? What the Lakes are telling us

Lloyd C. Irland
The Irland Group, Wayne, ME

A video of this presentation is available

Instrumental records of Maine air temperatures are rare before the turn of the 20th century.  Even then, geographic coverage is spotty. So, scientists studying climate change have employed lake ice regimes, summarized by ice-in and out-out dates, as proxies for changing climate and growing seasons. This talk analyzes ice-out data for a population of 36 Maine lakes. Statistical traits are noted, and then regional examples for the northern U.S. are cited as regional background. Geographic patterns within Maine for the full dataset are explored. These analyses show several patterns: 1) Patterns over time are not uniform across the state; 2) The dates can move away from longterm trends for considerable periods; 3) Limited data show that total ice free days per year can change by twice as much as do out days.; 4) Ice out dates respond strongly to mild longterm changes in annual or seasonal temperatures; and 5) A mystery is that in recent decades, for many of the sampled lakes, no statically significant trends in ice out dates is detectable though variability has risen notably.

Shifting baselines of lake water clarity in Maine: Applications for lake assessment in a changing climate

Jeremy Deeds1,2, Aria Amirbahman3, Stephen A. Norton4, Linda C. Bacon1,2, and Rachel A. Hovel5,

1. Maine Department of Environmental Protection, Augusta, ME
2. Ecology and Environmental Sciences Program, University of Maine, Orono, ME
3. Department of Civil and Environmental Engineering, Santa Clara University, Santa Clara, CA
4. School of Earth and Climate Sciences, University of Maine, Orono, ME
5. Division of Natural Sciences, University of Maine at Farmington, Farmington, ME

A video of this presentation is available

Lakes may exhibit changes in water clarity over time due to large-scale regional factors, such as fluctuations in weather patterns, in addition to the effects of local-scale land use changes. The interconnectedness of these factors can confound lake condition assessments. Data from reference lakes, which are in watersheds with minimal human influence, may be used to define benchmark water quality conditions for comparison to non-reference lakes. To disentangle related factors that complicate interpretation of lake condition over time, we constructed baseline trends of water clarity patterns for five types of Maine reference lakes using data collected by professional and citizen scientist lake monitors (1990-2018). Our analysis compares trends in lake clarity from individual lakes to baseline reference lake trends, accounting for variation due to regional factors and allowing for more informed single-lake condition assessments that focus on local impacts. To better understand the drivers of clarity trends in reference lakes, we applied a dynamic factor analysis (DFA) to the baseline trends from reference lakes. We identified two common trend patterns that were associated with different lake types to varying degrees. Precipitation during the stratification season (April-September) was the most important covariate for explaining variation in water clarity in reference lakes, with greater amounts of precipitation associated with lower water clarity. With climate change models forecasting increased precipitation in the future, baseline lake clarity across Maine is consequently expected to decline.