Toward a mechanistic understanding of coupled biogeochemical cycles in human-dominated landscapes

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Human activity is profoundly altering biogeochemical cycles, with important implications for the provision of ecosystem services that are vital to society. Sustainable nutrient management strategies in agriculture are a critical lever to reduce these impacts while supporting long-term food security and water quality. Yet, we have relatively limited understanding of how agricultural activities and urbanization affect the interaction among biogeochemical cycles (such as nitrogen, phosphorus, and carbon) that can in turn influence ecosystem services. Another management challenge is that we lack mechanistic models of how these human impacts on nutrient cycling moderate the provision of specific services. Closing these knowledge gaps related to human-dominated systems is critical as global food demand increases and urbanization continues. My research program will address these challenges while training students in statistical and spatial analysis, nutrient budget accounting, and ecosystem service modeling. A first objective for my students and I is to quantify the ratio of soil nitrogen, phosphorus, and organic carbon in diverse agroecosystems through synthesis of data from published studies worldwide. We will use these data to test to what degree climate, soil type, and farm management mediate soil nutrient ratios. Second, we will explore how specific nutrient management strategies affect soil nutrient balances and the provision of multiple ecosystem services using hypothesis-driven mechanistic models. Our primary focus will be on the relationship between agricultural nutrient use and water quality, including how shifts in the ratio of nitrogen versus phosphorus use affects water quality in downstream lakes and rivers across North America. A third objective focussed on urban areas is to quantify the magnitude and variation of nutrient and carbon flows from agricultural lands to cities. Our models will enable estimation of how much fertilizer use is embodied in urban diets and how this affects the capacity of local croplands to recycle nutrients from urban waste streams based on their nutrient ratios. These interrelated objectives will provide new understanding of how tightly flows of nutrients and carbon are linked within and across human-dominated landscapes, as well as how agricultural nutrient management could be a mechanism that drives changes in the provision of multiple ecosystem services over space and time. The overall goal of my research program is to help inform how we can balance competing aims to enhance agricultural productivity and environmental quality in an era of agricultural intensification and urbanization. Findings from my proposed studies will contribute to advancing interdisciplinary research on agricultural and urban dimensions of coupled biogeochemical cycles, with potential application for land managers and city governments in Canada and abroad.