Characterization of the shallow groundwater system in an area with thin soils and sinkholes |
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Authors: | James H Wiersma Ronald D Stieglitz Dewayne L Cecil Glenn M Metzler |
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Institution: | (1) College of Environmental Sciences, University of Wisconsin-Green Bay, 54301-7001 Green Bay, Wisconsin |
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Abstract: | Door County, Wisconsin, is a region of karst topography underlain by Silurian dolomite bedrock. Numerous sinkholes intercept
much of the surface runoff and act as sites for direct groundwater recharge. The clay-rich and impermeable Upper Ordovician
Maquoketa formation separates the dolomite aquifer from the deeper aquifers and appears to be a factor in groundwater circulation
and karst formation Thin glacial drift and Quaternary materials overlie the dolomite and are hydrologically connected with
it
The interactions of surface and groundwater, and the role of solution features in water interchange were studied in a small
drainage basin. This basin contains several large sinkholes and a nearby spring complex Mapping identified many additional
sinks and swallets in surface drainage routes Water flowing into two sinks was traced and found to have a residence time of
several hours. Water flowing into sinkholes and from the spring was sampled to identify the quality and seasonal trends in
composition of the shallow groundwater Water quality parameters monitored include magnesium, sodium, potassium, chloride,
phosphorous, nitrate and ammonia, nitrogen, alkalinity, pH, turbidity, and specific conductance. Nitrate levels were found
to increase 5 to 6 times during periods when there was zero input through sinkhole recharge sites. Nitrate levels approached
the 10 mg/l NO3
−-N limit set by the U.S. Public Health Service for drinking water
In this basin sandy soils are most susceptible to sink development, whereas clay-rich soils have a lesser number of sinks.
It appears, however, that a network of bedrock solution features exists under all soils The loss of soil into sinkholes has
impacted groundwater quality and reduced agricultural productivity through a reduction in tillable acreage and water retention
capacity. |
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Keywords: | |
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