Hydroclimatic Drivers on Groundwater Nitrate Variability in Western Wisconsin

Abstract

Wisconsin relies extensively on groundwater usage for both agricultural production and private use. Under a changing climate, significant precipitation and drought events are becoming more severe. Nitrate (NO3-) has become a prominent contaminant of concern due to its exceptional solubility in water, its ability to persist in aquatic systems, and its potential for adverse health effects such as methemoglobinemia in infants. In agriculturally intensive areas, nitrate concentration levels are linked with the usage of manure and certain fertilizer types. Regular monitoring of groundwater quality is essential to assess nitrate concentration amounts for potentially hazardous contamination levels. In partnership with a regional farmer-led watershed council, nearly one hundred wells have been sampled across western Wisconsin since 2018 to monitor groundwater quality at both seasonal and interannual timescales. In this time, the sampling region has experienced the wettest precipitation year on record along with three consecutive years of drought conditions. Nitrate concentration is then coupled with hydrological parameters such as recharge precipitation intensity to determine how climatic extremes can affect wells with greater fluctuations in their contaminant amounts. Wells within the sampling area can vary in depth and either draw water from the Prairie du Chien dolostone or Jordan sandstone aquifers. A sizable portion of the wells sampled have shown stable nitrate levels, with some showing slight increases or decreases during the testing period that could be correlated with overall precipitation patterns. Final nitrate analysis will be reported back to the farmer-led council to inform and support regional efforts towards sustainable land management and agricultural practices which aim to reduce nitrate and other contaminants from leaching into groundwater.