LONG-TERM CHANGES IN SEASONAL EPILIMNETIC TEMPERATURES IN LAKE MENDOTA AND TROUT LAKE: WISCONSIN’S SENTINELS OF LAKE WARMING

Lake Mendota (40 km², 25 m deep) and Trout Lake (16 km², 36 m deep) in southern and northern Wisconsin, respectively, are Univ. Wisconsin (UW)-Madison Center for Limnology’s flagship lakes. With laboratory facilities on their shorelines, the lakes have been the focus of a rich history of limnological research. Seasonal water temperature profiles were regularly recorded in Lake Mendota in most years since 1894 (except for 1930s-1940s when city monitoring data were lost). Seasonal profiles were first recorded in Trout Lake in 1914, but profiles were not regularly recorded until the summers of 1925-1941. Following those years, profiles were only recorded sporadically in Trout Lake until 1981 when the UW’s North Temperature Lakes Long-Term Ecological Research Project began studying lakes year-round in northern Wisconsin. Lake Mendota was added to the project in 1995. High coherency in epilimnetic (0-5 m) temperatures was found between Mendota and Trout. Since 1981 when both lakes were intensively studied, spring and summer epilimnetic temperatures have not increased significantly, but a modest increase did occur in Mendota since 1894. However, fall temperatures exhibited a large upward trend (delayed cooling) in both lakes’ shorter records, but not in Mendota’s longer record. Mendota’s summer trend was due to a higher frequency of warm summers in recent decades, not from an increase in maximum temperatures. Significant air-water temperature relationships were also found. Thus, the two lakes may be used as sentinels of water temperature responses to climate change in Wisconsin.

Primary Presenter: Richard Lathrop, University of Wisconsin-Madison (rlathrop@wisc.edu)

Authors:

Richard Lathrop, University Wisconsin-Madison, Center for Limnology  (rlathrop@wisc.edu)

Dale Robertson, U.S. Geological Survey, Upper Midwest Water Science Center  (dzrobert@usgs.gov)

John Magnuson, University Wisconsin-Madison, Center for Limnology  (john.magnuson@wisc.edu)

Stephen Carpenter, University Wisconsin-Madison, Center for Limnology  (steve.carpenter@wisc.edu)

Emily Stanley, University Wisconsin-Madison, Center for Limnology  (ehstanley@wisc.edu)

Mark Gahler, University Wisconsin-Madison, Center for Limnology  (gahler@wisc.edu)