Background  

One predicted outcome of global climate change is warming of the Earth's atmosphere as a result of the greenhouse effect.  Such a climate change would most likely affect Great Lakes wetlands through its effect on water levels in the lakes and ground-water systems feeding the lakes.  Lake level is the primary factor controlling shoreline behavior and ultimately the status of Great Lakes coastal wetlands, but the mechanisms of this control and its long-term dynamics are still poorly understood.

This study provides long-term data on the responses of wetlands at three different latitudes in the Lake Michigan basin, three longitudes in the Lake Superior basin, and three latitudes in the Lake Huron basin to warming and cooling events over the past 4000 years through the use of sedimentological and paleoecological analyses of sediment cores.  We hypothesize that Great Lakes wetlands will respond to future warming events and water-level changes in much the same manner that they did in the past.  Therefore, past responses of wetland plant communities can be related to current conditions and used as a predictor of future responses should global warming become a reality.

Description of work to be done

Each area to be studied contains a series of fossil beach ridges laid down in response to water-level fluctuations over the last several thousand years.  As each ridge formed, a wetland developed in the swale behind it. These wetlands persist today.  The ridge/swale complexes comprise chronosequences that record changes in lake level over time (the positions and elevations of the ridges) and wetland response to those changes (the present wetland vegetation and the record of past vegetation preserved in peat deposits).  Research in these chronosequences involves developing lake-level histories for each site based on sedimentological studies; developing long-term, lake-wide water-level histories by combining data from multiple sites; developing models of ground-water flow at each site based on hydrogeological studies;  developing long-term histories of past vegetation changes at each site based on paleoecological studies; developing models of modern plant communities at each site based on plant ecology studies; and combining all datasets to develop an understanding of past wetland response to changes in climate.  Field studies include ten primary locations:

Lake Michigan
1. North end, near Thompson and Manistique, Michigan
2. East shore, Sleeping Bear Dunes National Lakeshore (Platte Lake), Michigan
3. South end, within and near Indiana Dunes National Lakeshore (Toleston Beach), Indiana

Lake Superior
4. Grand Traverse Bay on the Keweenaw Peninsula, Michigan
5. Au Train Bay near Munising, Michigan
6. Tequamenon Bay between Sault St. Marie and Whitefish Point, Michigan
7. Batchawana Bay to the northwest of Sault Ste. Marie, Michigan

Lake Huron
8. St. Vitals Bay near DeTour Village, Michigan
9. Thunder Bay and Negwegon State Park near Alpena, Michigan
10. Albert Sleeper State Park near Port Austin, Michigan

General Approach

           
Our past work produced a 4700-yr record of lake levels that serves as a proxy for climate change in the upper Great Lakes; paleoecological data that showed the response of wetland plant communities to past climate changes; modern vegetation data that correlated present plant communities with those characterized in the paleoecological record; and hydrologic data that suggested the importance of ground water in determining the localized response to climate change.  The objectives for current work in this study are to meet the critical needs identified by our past work: develop a better understanding of ground-water influences, isostatic rebound, and tectonic events; obtain better resolution of lake level and climate changes over the past 1500 years and during the abrupt climate change from 4500 to 4000 years ago; implement testate amoebae paleohydrologic methods to develop additional proxies for climate change; implement all study methods in at least one site that contains a nearly complete record of ridges and swales; and develop meteorological transfer functions for our climate proxies to assist in management applications.  We are developing ground-water hydrology methodologies in two previously studied ridge and swale sites; conducting peatland paleohydrologic studies at several additional sites to develop strong and spatially explicit records of climate change; vibra-coring several additional ridge and swale systems to address the hydrograph, climate proxy, isostatic rebound, and tectonism questions; and conducting these and additional paleoecology and plant ecology studies at sites on Lake Huron that contains over 100 beach ridges encompassing the abrupt lake-level fall from 4500 to 4000 years ago and containing a large number of beach ridges and wetlands from the most recent 1500 years.  We will then develop the transform functions to assist management.  Study results will address sensitivity, causal mechanism, variability, and paleo-approach goals of the 5-yr Global Change Program; climate variability/change, water cycle, and ecosystems goals of the USCCSPSP; and will continue to assist in DOI and federal land-management decision-making.

Value of Work

Studies of these chronosequences will allow us to

1. determine long-term water-level changes that occurred in lakes Michigan-Huron and Superior during past climatic changes;
2. determine site hydrology and identify hydrologic changes related to climate change;
3. determine vegetational response to past lake-level, ground-water, and climate changes from the paleoecological record; 
4. determine current vegetational patterns in the wetlands we are studying;
5. predict the responses of present-day wetlands to global warming; and
6. provide natural resource managers with information that can be used to protect or preserve populations, habitats, and ecosystems that could be threatened by future changes in climate.