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Groundwater Nitrate in Three Hydrogeologic Settings Throughout Southwestern Ontario

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Title: Groundwater Nitrate in Three Hydrogeologic Settings Throughout Southwestern Ontario
Author: Gardner, Scott
Department: School of Engineering
Program: Engineering
Advisor: Levison, Jana
Abstract: Groundwater quality can be impacted by non-point source pollution from agricultural activities. The objective of this research is to better understand how different environmental conditions effect groundwater nitrate contamination in southwestern Ontario. Groundwater nitrate concentrations, along with multiple other hydrogeochemical parameters (e.g. pH, ORP, DO, DOC, EC, sulfate, chloride, temperature, isotopes) were measured at 25 different monitoring wells located at three research sites (Norfolk, Guelph, and Acton), bi-monthly (once every two months) from June 2014 to July 2016 (13 sampling events). Hydrogeologic settings of these three unique sites were characterized through descriptions of their climate, land use, soil, and the subsurface. The Norfolk research site comprises a thick sand and gravel unconfined aquifer. At the Guelph research site (located at University of Guelph Arkell Research Station) there is a fractured limestone/dolostone bedrock aquifer, overlain by sand and gravel. The Acton research site comprises a fractured limestone/dolostone aquifer, overlain by a very thin layer of diamict. Data were interpreted via statistical methods (multiple linear regression analysis aka MLRA), geographic information systems (GIS) analysis, and time series analysis. Each of the three research sites displayed different trends of nitrate contamination over the study period. The Guelph site experienced peaks in nitrate concentrations in spring of 2016 after a drought period in summer of 2015. The Norfolk site displayed concentrations which align with what is expected from a continuous nitrate source, although certain wells had concentration peaks like the Guelph site. The Acton site experienced consistent nitrate concentrations which did not vary significantly over the study period. Evidence from groundwater geochemical 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.
Date: 2017-09
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