Assessment of the source and mobility of phosphorus in the hydrologic system in western Wisconsin

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  • Sarah Vitale, UW-Eau Claire
  • Brian J. Mahoney, UW-Eau Claire

Phosphorus loading in Wisconsin is responsible for significant lake eutrophication throughout the state, with severe societal and economic impacts, including a loss of recreational tourism, reduction of commercial fisheries, and a decrease in biodiversity. Historically, the P source has been attributed to agricultural inputs delivered by surface water runoff; however, ongoing investigations at UW-Eau Claire suggest that P source and mobility through the hydrologic system is much more complex, and that significant non-point sources of P may include both agriculture and naturally-occurring P in the bedrock. These investigations have demonstrated that P concentrations are exceedingly high in the groundwater (often exceeding the WI surface water regulatory limits of 15-100 ppb), that P is highly mobile in the subsurface, and that these high groundwater P concentrations may contribute to lake eutrophication.

This investigation aims to delineate (1) probable phosphorous sources and mechanisms for mobility in groundwater aquifers through a regional analysis of water quality in western Wisconsin, and (2) evaluate the role of nutrient loading through groundwater discharge into lakes via a case study investigation of Mud Lake (Barron County, WI). This study is critical in developing a better understanding of phosphorus source and mobility in western Wisconsin. Effective non-point source contaminant remediation, lake management, and land use practice regulations cannot be successfully employed without a comprehensive understanding of the behavior of phosphorous throughout the regional hydrologic system. The results of this investigation will be of interest to regional and state organizations focused on the research and management of water resources, including the Wisconsin Department of Natural Resources (WDNR), the West Central Wisconsin Regional Planning Commission, and the U.S. Geological Survey.

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