MODELING MITIGATION STRATEGIES FOR SLOUGH MANAGEMENT IN SAUK COUNTY, WI

Sloughs along the Lower Wisconsin River act as a refuge and nursery habitat for riverine fish species, including the endangered Starhead topminnow. These sloughs 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 within 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.

The objectives of this study are to identify key recharge zones contributing to the lakes and to evaluate the effectiveness of nutrient mitigation strategies for the sloughs. 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. Samples for nitrate, phosphate and dissolved oxygen concentrations, as well as stable isotopes of oxygen and hydrogen, were collected to provide additional constraints on groundwater flow paths and on potential recharge area nutrient sources. The model is being used to test the impact of constructing buffer zones and/or induced discharge sites on groundwater nutrient loading to the sloughs, as well as Implications for land management.