DEVELOPING A GROUNDWATER FLOW MODEL FOR SLOUGH MANAGEMENT IN SAUK COUNTY

Sloughs along the Lower Wisconsin River act as a refuge and nursery habitat for riverine fish species, including the endangered Starhead topminnow. They are also an important local economic resource for tourism and personal recreation such as fishing and boating. Since 2008, there has been a marked decrease in the water quality of the Lower Wisconsin River floodplain lakes. In particular, high phosphorus and nitrogen concentrations, low dissolved oxygen levels, and dense metaphyton cover have been observed in these groundwater-fed lakes located with Sauk County, WI. Although the exact causes for the deterioration in water quality are unclear, nutrients applied via fertilizer and manure to sandy soils in the agricultural areas of the adjacent Pleistocene terrace are likely contributors to the problem.

Numerous studies have delineated capture zones to protect water quality of high capacity wells, but few have investigated their application with regard to protecting ecological resources - which have more diffuse and variable groundwater contribution areas. This study seeks to identify key recharge zones contributing to the lakes and evaluate the effectiveness of “groundwater buffers” for mitigating nutrient loading. The primary tool for this work is a three-dimensional groundwater flow model developed as part of a Wisconsin DNR River Planning grant. Calibration targets include water level data collected over several years of continuous monitoring at over 20 well sites within the floodplain and along the river itself. More recent sampling efforts have included nitrate, phosphate and dissolved oxygen concentrations as well as stable isotopes of oxygen and hydrogen, which will provide additional constraints on groundwater flow paths and on potential recharge area nutrient sources.