Anthropogenic phosphorus (P) inputs into agricultural soils have exceeded crop demand for decades. The resulting release of the excess P to surface water contributes to eutrophication, including the occurrence of harmful algal blooms (HABs), with severe threats to drinking water security and aquatic ecosystems. In particular, HABs may cause the appearance of oxygen deficient "dead zones" in lakes and coastal marine areas. Efforts to reduce the inputs of P to Canadian agricultural soils started in the late 1970s-early 1980s, but the expected decrease in P loading to surface water was not observed. A likely reason is the presence of legacy P accumulated in the soils of agricultural watersheds, due to previous fertilizer application. Thus, even after reducing P inputs, legacy P continues to be exported from the soils after several decades. Agricultural P soil legacies are therefore a major concern for decision makers and stakeholders.
For this project, I will locate and quantify agricultural legacy P in the watersheds that drain into the Laurentian Great Lakes (LGL). Lake Erie especially continues to experience extensive HABs, while nuisance algal blooms are a local problem in all LGL, excluding Lake Superior. My initial focus will be on the agricultural P storage in the soils and groundwaters of southwestern Ontario. I will use a mass balance modeling approach, combined with data mining (land use, fertilizer application rates) to compute the evolution of legacy P from the late 1800s to today. The mass balance model will be implemented into a Geographical Information System (GIS) platform to create maps that delineate the accumulation and depletion of legacy P within the landscape. These maps will inform nutrient management and abatement strategies.
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