Author(s):
Samantha W Kaplan* - University of Wisconsin - Stevens Point
Paul J Garrison - Wisconsin Department of Natural Resources
Joy Stelzer - University of Wisconsin - Stevens Point
Abstract:
A recent seven year drought in northern Wisconsin resulted in lowered lake levels and a concomitant impact on the fishing and tourism economy. High rainfall in the summer of 2010 raised most lake levels, but seepage lakes and groundwater levels remain depressed. Hydrological models suggest small seepage lakes that sit high on the landscape should experience decreased alkalinity as groundwater levels, and hence cation contribution to lake recharge, are reduced during drought. To test this model, a 536 cm sediment core from Max Lake in Vilas County, Wisconsin, representing 12,500 years of depositional history, is being used to reconstruct episodes of past drought and concurrent changes in lake pH. Loss on ignition (LOI) and charcoal accumulation rates (CHAR) are being used to identify past drought events, while shifts in diatom assemblages indicate changes in lake alkalinity. Charcoal morphology is being used to infer whether past fires were canopy or ground fires and to estimate their relative intensity, and charcoal size class is used to suggest fire proximity. Initial results reveal periods of increased fire frequency in the early-to-mid Holocene and again during the Medieval Warm Period circa 800 yr BP. This is in keeping with other proxy evidence of decreased precipitation in the Northwoods region. Ongoing diatom analysis will reveal whether lake pH was reduced during these events.
