Lake surface water temperatures are warming worldwide, raising concerns about the future integrity of valuable lake ecosystem services. In contrast to surface water temperatures, we know far less about what is happening to water temperature beneath the surface, where most organisms live. Moreover, we know little about which characteristics make lakes more or less sensitive to climate change and other environmental stressors. We examined changes in lake thermal structure for 231 lakes across northeastern North America (NENA), a region with an exceptionally high density of lakes. We determined how lake thermal structure has changed in recent decades (1975-2012) and assessed which lake characteristics are related to changes in lake thermal structure. In general, NENA lakes had increasing near-surface temperatures and thermal stratification strength. On average, changes in deepwater temperatures for the 231 lakes were not significantly different than zero, but individually, half of the lakes experienced warming and half cooling deepwater temperature through time. More transparent lakes (Secchi transparency >5 m) tended to have higher near-surface warming and greater increases in strength of thermal stratification than less transparent lakes. Whole-lake warming was greatest in polymictic lakes, where frequent summer mixing distributed heat throughout the water column. Lakes often function as important sentinels of climate change, but lake characteristics within and across regions modify the magnitude of the signal with important implications for lake biology, ecology and chemistry.
Bibliographical noteFunding Information:
The Global Lake Ecological Observatory Network (GLEON) made this project possible, and the project was initiated at the GLEON 16 meeting in Jouvence, Qu?bec, Canada; support for analyses and travel were provided by GLEON and NSF EF-1137327 and EF-1346856. SJM was supported by a Natural Science and Engineering Research Council of Canada (NSERC) Discovery grant; RMP by Miami University College of Arts and Sciences and Eminent Scholar funding; and ALH by the United States Department of Agriculture National Institute of Food and Agriculture, Hatch Project #0226747. We acknowledge data providers and collaborators and their organizations who contributed data and project conceptual development: Charles Boylen, Sandra Nierzwicki-Bauer, and Lawrence Eichler (Darrin Freshwater Institute); Matt Albright and Holly Waterfield (SUNY Oneonta); M. Brown and J. Halfman (Hobart andWilliam Smith College); Denise Bruesewitz (Colby College); Michael Clancy (New York State Department of Environmental Conservation); Bruce Gilman (Finger Lakes Community College); Terry Gronwall (Honeoye Lake Watershed Task Force); Nelson Hairston and Seth Schweitzer (Cornell University); Elizabeth Herron (University of Rhode IslandWatershedWatch); Daniel Josephson and Clifford Kraft (Cornell University Adirondack Fishery Research Program); Jen Klug (Fairfield University); Corey Laxson (Paul Smiths College); Dean Jeffries and Fred Norouzian (Environment Canada); Robyn Smyth (Bard College). We thank the following data providers: FirstLight Power Resources, Linda Green, Arthur Gold, Linda Bacon, Maine Department of Environmental Protection, Maine Volunteer Lake Monitoring Program, National Park Service, Bill Gawley, Acadia National Park, Sara Steiner, Melanie Titus, Scott Ashley, New Hampshire Department of Environmental Services, Gene Likens and Thomas Winter (Hubbard Brook Data Archive), Lake Sunapee Protective Association, Cornell Biological Field Station, Canandaigua LakeWatershed Council, Kelly Seelbach, Richard Van Dreason, New York City Department of Environmental Protection, Upstate Freshwater Institute, Michael Martin, Daniel Kelting, Honeoye Lake Watershed Task Force, FUND for Lake George, Mohonk Preserve, Finger Lakes Institute, Dorset Environmental Science Centre, Andrew Paterson and Ron Ingram, Harkness Research Laboratory, Trevor Middel, Mark Ridgeway, Brian Shuter, Gregory Wacik, United States Army Corps of Engineers, Blooming Grove Hunting & Fishing Club, Lacawac Sanctuary Field Station, Lake Wallenpaupack Watershed Management District, Nick Spinelli, Vermont Department of Environmental Conservation. For all Sen's slopes used in this study, see Table S2 for the 1975 cohort and Table S3 for the 1985 cohort. For data repositories, contacts and access for all original lake temperature data, see Table S4.
- Climate change
- Lakes as sentinels
- Thermal stratification