PARENT SESSION
Oral Session #10: Paleoecology. Presiding: S. Hotchkiss.
Monday, August 6, 2001. 8:00 AM to 12:00 PM. Hall of Ideas J.
Holocene lake-level changes and their relationship to vegetational change at two sites in the Midwest.
EWING, HOLLY1,2, 1 2
ABSTRACT- Although strong evidence for lower lake levels during the middle Holocene exists in areas currently along and west of the prairie-forest border, evidence for changes in moisture availability to the north and east is less conclusive. In this study, stratigraphic evidence from transects of cores at two sites in the Great Lakes region reveal periods of lower and fluctuating lake levels. Changes in sediment characteristics suggest that both lakes were probably shallowest between approximately 8000 and 6000 cal yr BP with higher lake levels later in the Holocene. The evidence for rising lake levels in the late Holocene is consistent with other records from this region. However, the increase from low lake levels around 6000 cal yr BP to high lake levels after approximately 2000-3000 cal yr BP was not monotonic. Instead, strong evidence for fluctuating lake level between 4700 and 2750 cal yr BP at one site and less clear evidence of the same at the second site between 5400 and 3950 cal yr BP suggests a highly variable moisture regime in the middle Holocene. Both species composition and the timing of changes in vegetation differed between these sites during the middle Holocene. Differences among species in drought tolerance, as well as the variability in soil moisture-holding capacity across the landscape, may explain the lack of a cohesive response in vegetation to this climatic variability.
KEY WORDS: lake-level change, paleoecology, vegetation response, climatic variability