| dc.description.abstract | Within the Great Lakes region, agricultural non-point source nitrogen (N) and phosphorus (P) contamination contribute to algal blooms and decreased water quality, particularly from tile-drained landscapes. These water quality challenges are accompanied by anthropogenically induced increases in greenhouse gases within the atmosphere, which are leading to changes in climate, which may in turn exacerbate water quality issues by changing hydrological and biogeochemical cycling. This may be particularly important during the non-growing season (NGS), during which most of the annual nutrient export and flow occurs in the Great Lakes region. However, hydrologic and biogeochemical processes during the NGS are less well understood compared to the growing season. The implementation of beneficial management practices (BMP) such as controlled tile drainage (CD) have the potential to mitigate both current and future water quality issues. However, there is little information on the potential water quality tradeoffs associated with this particular practice under both contemporary and future climates. Such information is necessary before CD may be widely recommended and adopted as a BMP. In this thesis, the Soil Water Assessment Tool (SWAT) model was used to demonstrate the potential for CD to reduce nutrient losses in midwestern Ontario, under both current and future climates, and to understand the processes affecting nutrient export responses through the analyses of the water balance, flow regimes, and weather patterns, and to examine seasonal differences in these variables. In this study, two Soil Water Assessment Tool (SWAT) models were applied at varying scales. One was generated for the Medway Creek watershed, near London, ON, to understand the impact of climate change on water quality and quantity by forcing the model with a bias corrected general circulation model (GCM) ensemble. The second SWAT model was run at the field scale, for a field site near Londesborough, ON to understand the potential water quality tradeoffs associated with CD for a field with low-sloped clay loam soil. Results indicate that future changes in climate will cause shifts in seasonal water budgets, resulting in much greater nutrient export during the NGS and an overall increase in annual nutrient losses by the 2080-2100 period. These changes will be driven by precipitation quantity, but also changing precipitation characteristics (timing, form, magnitude, and frequency) and temperature, which will influence runoff pathways. The use of CD will not mitigate water quality issues and will instead exacerbate TP losses in runoff by increasing soil moisture and consequently increasing surface runoff. Although reductions of tile flow were greater than the simulated increases in surface runoff, the approximately 10X greater TP concentrations in surface runoff resulted in an overall increase in simulated edge-of-field TP losses. This will be particularly problematic where CD is used both during the NGS and growing season. This thesis has provided an improved understanding of the impacts of climate change on water quality in the MCW, and has demonstrated that CD has little potential to mitigate water quality issues in the present or future. This thesis has also demonstrated that understanding nutrient export processes during the NGS will be increasingly important for increasing BMP efficacy, reducing NPS contamination, and the occurrence of harmful algal blooms. | en |
