Excess phosphorus (P) loading increases the frequency of harmful algal blooms (HABs), posing severe threats to drinking water security and aquatic ecosystems. Efforts to reduce the inputs of P to Canadian agricultural soils started in the late 1970s-early 1980s, and were initially successful, but surface water P loading became persistent again in the 2000s. HABs were a problem in the southern Laurentian Great Lakes (LGL) before the initial nutrient mitigation efforts, and the re-emergence of HABs in Lake Erie in the 2000s was in part a result of legacy P that had accumulated in soils and groundwater in agricultural watersheds. Legacy P exists as a result of historical inputs of P, typically fertilizer used in excess of crop needs. Consequentially, even after reducing P inputs, legacy P continues to be exported from soils after several decades. In Chapter 2, a large-scale mass balance was conducted for the Ontario watersheds to locate and quantify agricultural and other anthropogenic P inputs from 1961 to 2016, utilizing existing datasets as well as historical reconstructions of P inputs to the landscape. This scale of P mass-balance has not been completed before in Ontario. The mass balance model was implemented into a Geographical Information System (GIS) platform to delineate potential areas with legacy P accumulation and depletion within the landscape. These maps identified areas with high P inputs and large potential stores of legacy P. Historically, southwestern Ontario has had the densest agriculture and populated areas in Ontario and has had high P inputs over time. County-scale trends such as shifts to intensive livestock or crop-based agriculture, or increasing urbanization were also identified. In Chapter 3, the fate and transport of P and the possible development of P legacies was explored in the context of risk. P export is influenced by environmental conditions in soil, as such, there is spatial variance in the likelihood that P will runoff or accumulate in soils. The environmental conditions may therefore be used to represent the vulnerability of the system and the risk to either lose or accumulate P. The cumulative agricultural P surplus map was used in conjunction with vulnerability maps to construct soil P risk maps. Different vulnerability models were explored, and ultimately soil erosion potential maps were used to identify vulnerable areas with a high risk of P losses to surface water and areas with a high risk of P accumulation in soil. It was determined that there was a higher risk of P accumulation in soil along the coast of Lake Erie, and it is possible that P legacies exist in these areas. The results inform nutrient management and abatement strategies and the adaptive implementation of conservation practices.

The work presented in this thesis aimed to demonstrate the use of remote geophysical methods and numerical modelling to address questions related to hydrogeological processes in freezing soils. Two different study areas and research questions were investigated: In chapter 1, Landsat 4-5 TM and RapidEye-3 datasets were used to identify groundwater discharge zones in the Central Mackenzie Valley of the Northwest Territories. Given that this area is undergoing active shale oil exploration, identification of groundwater discharge zones is of great importance. Discharge zones represent groundwater-surface water interaction points that are potential pathways for contaminants associated with hydraulic fracturing to move. Following the works of Morse and Wolfe (2015), a series of image algorithms were applied to imagery for the entire Central Mackenzie Valley, and for the Bogg Creek Watershed (a sub watershed of the CMV) for selected years between 2004 and 2017. The algorithm series extracted ‘icings’ from the images. Icings (also called aufeis) are surface ice lenses where groundwater discharges in the winter months, then freezes. Icings were statistically examined for all of the selected years to determine whether a significant difference in their occurrence and size existed. It was concluded that there was a significant difference in the spatial distribution of icings from year to year, but that there were several places where icings were recurring. During a field visit in August of 2018, high resolution thermal imagery was captured for several of these locations and it was found that groundwater was also discharging in the summer. This provides strong evidence to suggest that the recurring icings represent springs from which groundwater discharges year-round. These springs represent ideal locations to monitor the quality of discharging groundwater following the establishment of fracking operations. Furthermore, identifying these monitoring points remotely is expected to have drastically reduced the field efforts that would have been required to find them in situ. This thesis demonstrates the value of remote geophysical methods for hydrogeological applications, particularly in areas that have limited accessibility. The second component of this thesis establishes a conceptual model that describes the processes which influence winter subsurface pipe and water main breakage in Southern Ontario. Recent winters in this region have seen a dramatic increase in the number of pipe/main breaks that occur above the regional water table, but below the freezing front. Though subsurface pipe breakage is well-understood in saturated conditions or in the case when it is encompassed within the freezing zone, it is not well understood in the conditions of unsaturated soil which is not frozen, but contains a frozen zone above it. It is hypothesized that differential stress may be exerted on a pipe as soils of different frost heaving potential freeze and expand above the pipe. Once a certain overburden pressure is exceeded and upward frost heaving is no longer possible, it is expected that subsequent freezing will exert force onto the soil skeleton (and therefore pipe) below it. Two specific conceptual problems are developed in this work, and the processes which affect the distribution of stress in each case are described in detail. Then, a plan for the numerical implementation of each problem using the finite element model ABAQUS is given. Though the numerical models are not shown in this work, the conceptual models provide the framework which is necessary to implement a successful numerical model. The problem of pipe breakage in the unsaturated zone is complex and requires the coupling of equations which describe groundwater flow, stress-strain in a porous medium, and heat transport. Therefore, it was vital for an in-depth conceptual understanding of the problem to be established before introducing the numerical application.