Effects of Glacial Sediment Type and Land Use on Nitrate Patterns in Groundwater

Growing population centers such as those in southern Ontario rely on fractured bedrock aquifers for drinking water. A threat to these aquifers is posed by surficial nonpoint‐source pollution infiltrating with rainwater and moving through the overlying Quaternary glacial deposits. Investigation of local unconsolidated sediments, and the factors affecting contaminant transport through these, is needed to assess risks to the quality of underlying groundwater resources. In this study, sites with a variety of agricultural land management practices and glacial geologic settings were investigated by employing high‐resolution data collection methods. Geologic data from continuous sediment cores were combined with depth‐discrete hydrogeologic and geochemical parameter measurements using high‐resolution multilevel monitoring wells. Within a relatively small geographic area with three distinct glacially derived sediment types, the three sites exhibited greatly disparate vulnerability to nitrate contamination. The geologic setting, including surface topography and architecture and heterogeneity of sediment types at depth, influenced groundwater flow paths and water geochemistry, and subsequently, nitrate distribution. Although management practices influence the quantity of pollutants leaching to groundwater resources, the physical and chemical properties of the subsurface related to the geologic setting ultimately determine the persistence or attenuation of nitrate, and therefore become important to characterize when evaluating best nutrient and waste management practices.