INFERRING LAKE AND WETLAND SEDIMENT CONDUCTIVITY VARIATIONS FROM EM31 DATA AT THE WAUBESA WETLANDS NEAR MADISON, WI

Collection of geophysical data has various geologic applications that aid in interpreting subsurface geology and hydrology. The Wisconsin Geological and Natural History survey staff are collecting dense data sets from representative streams across Wisconsin’s physiographic regions including various physical properties, such as ground conductivity, basic stream chemistry, water temperature, and water depth. Instruments are mounted in a canoe in a controlled float to collect data, which is georeferenced to provide detailed information about spatial variability.

We employed these continuous data collection methods at the Waubesa Wetlands near Madison, WI. Water depth and water specific conductivity data were combined with EM31 conductivity results to create a multi-layered model, which determined variations in lake and wetland sediment electrical conductivity. Results of this application indicate spatial variations that provide insight into the depositional environment within the lake and wetland, in addition to the groundwater-fed spring pools near the northwestern region of the lake. Spatial variations in sediment and water conductivity correlate with variations in water temperature and pH.

Our established water quality and geophysical data collection methods are inexpensive, fast, and reliable, which qualify them as excellent tools to provide readily available input data for conceptual models. Ultimately these models will improve our understanding of ground- and surface water interactions in complex hydrogeologic systems throughout Wisconsin. Developing such local and regional conceptual models across Wisconsin also provide information useful to management of sensitive wetland habitats.