EFFECTS OF GLACIAL SEDIMENT TYPE AND LAND USE ON DISTRIBUTION OF NITRATE AND E. COLI IN GROUNDWATER

Quaternary glacial deposits underlie many agricultural regions in North America and beyond. Granular aquifers within these deposits, or bedrock aquifers underlying them, are potentially at risk of contamination from a variety of non-point source contaminants associated with agricultural activities. Although, nitrate and Escherichia coli distribution can broadly be thought of as homogenous at surface, the glacial deposits these contaminants travel through can be highly heterogeneous, making prediction of their transport and fate challenging. The distribution of nitrate was investigated at three sites to explore the role of land management practices and the subsurface environment on transport and fate of nitrate at depth. The behaviour of E. coli was also investigated at one of the sites. The study sites have varying land use and underlying sediment type: i) forested with no agricultural land use since the 1960s located on a hummocky end moraine; ii) an agroforestry plot with annual fertilizer inputs located on a drumlin; iii) a conventional cropped field with annual fertilizer and liquid swine manure inputs located on an outwash plain. At each site, cores were extracted from surface through the sediment to 3 m into bedrock and logged in detail. Sediment samples were taken for detailed grain size analyses and geochemical analyses (incl. Nitrate-N, Ammonium-N, solid organic carbon and total sulphur). Multilevel monitoring wells were then installed at all three sites, with depth discrete weekly water level measurements and groundwater geochemical sampling (incl. Nitrate-N, Ammonium-N, dissolved organic carbon and tritium) carried out at regular intervals over a period of one year, targeting spring, summer and fall conditions. E. coli concentrations were also monitored over a five month period prior to and following spring application of manure. For nitrate, results show that geology played a significant role in determining its subsurface distribution by influencing the hydrogeological and geochemical conditions at depth. For E. coli, results show that microbial contamination of aquifers can occur within a week of surface application, despite a 13 m thick vadose zone. Results of this study suggest subsurface heterogeneity needs to be better incorporated in best management practices or time of travel estimates.