Groundwater Nitrate in Three Hydrogeologic Settings within Southwestern Ontario

Abstract

Groundwater nitrate concentrations, along with other hydrogeochemical parameters (e.g. oxidation-reduction potential, dissolved organic carbon, sulfate, isotopes: nitrogen-15 and oxygen-18 in nitrate) were measured at 25 different monitoring wells located at three research sites (Norfolk, Guelph, and Acton), once every two months from June 2014 to July 2016. To identify trends in groundwater nitrate-nitrogen concentrations and to attempt to understand them, the hydrogeologic settings of these three unique sites were characterized by their climate, land use, soil, hydrochemistry, and hydrogeology. The research sites are comprised of; a thick sand and gravel unconfined aquifer; a fractured limestone/dolostone bedrock aquifer; overlain by sand and gravel; and a fractured limestone/dolostone aquifer, overlain by thin diamict. Evidence from groundwater hydrochemical analyses suggests that denitrification may be occurring at some of the deeper monitoring wells while evidence for nitrification was found at shallower depths. By determining which environmental and anthropogenic factors impact nitrate contamination in groundwater land managers can be informed to avoid further contamination of underlying groundwater resources.