Trends in Groundwater Levels in Central Wisconsin.

For the past 10 years the Central Sand Plain of Wisconsin, especially Portage and Waushara counties, has experienced an alarming decrease in groundwater elevation, lake levels, and stream flows, with significant impacts on aquatic ecosystems, recreational uses of streams and lakes, and property values of riparian lands. Using data from previous groundwater studies and our measurements, we estimate that water table levels have dropped at the rate of over 30 cm per year since 2002. During February and March 2008, under snow covered ground, measurements revealed a further decrease of 4.3 cm per month. At this rate, in the absence of recharge the water table will drop approximately 50 cm in 2008. It is clear that reduced stream flows and lake levels are associated with reduced groundwater elevations. However, over periods of years there is no clear relationship between groundwater elevation and precipitation. It is unclear the degree to which these groundwater fluctuations are driven by climate or increasing irrigated agriculture. The area of irrigated land in Portage and Waushara County increased 85% and 34%, respectively, between 1982 and 2002.  Thus, a broader scale project was initiated to document vegetative cover changes over the past 50 years, and simulate and measure groundwater balances for these various vegetation covers to partition climatological and agricultural influences on groundwater in the region.