Assessment of the Source and Mobility of Phosphorus in the Hydrologic System in Western Wisconsin

Abstract

Lake eutrophication due to nutrient loading from phosphorus (P) is a growing problem across the Midwest, causing a loss of aquatic biodiversity, damage to fisheries, and adverse impacts on human health. Although eutrophication is often blamed on anthropogenic sources, preliminary results suggest significant amounts of nutrient loading may be petrogenic. This investigation’s objectives are to distinguish the source of P contamination in surface and groundwater in western Wisconsin and to understand the mechanisms behind P mobility in the regional hydrologic system since P has been historically considered immobile in groundwater systems. The project includes a regional analysis of surface and municipal well groundwater samples in western WI, measured for P, iron, manganese, nitrate, and basic water quality parameters, to obtain a baseline spatial P distribution and an understanding of the geochemical environment. Sequential extraction analyses of P-bearing geologic units help determine the natural conditions under which P may be mobilized. Results demonstrate groundwater P concentrations frequently exceed WI surface water regulatory limit (max 100 ppb), and that P is highly mobile along flow pathways into lakes and streams. This research is important in developing a comprehensive understanding of P migration in Wisconsin’s regional hydrologic systems to implement effective waterway management.