Date of Award
Master of Science (MS)
Increased ground and surface water contamination has fueled the need for a better understanding of factors affecting hydrogeological settings. Seasonal variability in the recharge of an aquifer can affect the rate and amount of contamination that can occur. Stable isotopes have been previously investigated as tracers to determine flow paths of the water and contaminants. In this study, oxygen isotopes were used to determine the factors that influence seasonal variations in ground and surface water, such as well location, aquifer type, surface water sites, and soil type. Samples were collected from different locations around the Canajoharie Field Site, including wells that were screened in an unconfined aquifer, wells screened in confined aquifers, tile drains, and surface water sites, in an attempt to determine differences in seasonal variation.
The proximity of the wells to the Canajoharie Creek affected the seasonal variation of both water table elevation and oxygen isotopic composition of well water. The closer the well to the stream, the greater the response to storm events and seasonal changes. Wells along fence and tree lines show more of an influence during spring snowmelts than wells located in the middle of the fields, due to snow drifting from open areas to the fence and tree lines, resulting in a disproportionately large amount of recharge. The confined aquifers show little to no seasonal and storm event response.
Samples collected from two tile drains show that soil type also affects the recharge response. Soils with lower porosity, i.e. clayey soils, displayed macro pore flushing following storm events, whereas more porous sandy soils showed better water mixing capabilities. The samples collected from the tile drains were also analyzed for the herbicide metolachlor, and two metabolite compounds, metolachlor ESA (ethanasulfonic acid) and metolachlor OA (oxanilic acid), that are found in higher concentrations and persist longer than the parent compound. The oxygen isotopic composition of the tile drain water was compared with the ratios of metolachlor ESA to metolachlor (SAM ratio) and metolachlor ESA to metolachlor OA (SAO ratio) to illustrate macropore flushing and to determine how residence time of groundwater affects the herbicide degradation. A larger decrease in SAO ratios in the clay soil is the result of macropore flow which causes the breakdown of the less stable metolachlor OA in the infiltrating water. Pore water has a longer residence time in clayey soil, resulting in a higher SAM ratio in the water subsequently flushed out during storm events. Sandy soil retains less water in the pores, the briefer soil-water interaction resulting in lower metolachlor ESA production and lower SAM values.
Nadeau, John M., "Oxygen isotopes and metolachlor residues in water samples from a portion of the Canajoharie Creek watershed, central New York" (2000). Geology Theses and Dissertations. 42.