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

人类活动正在深刻地改变生物地球化学循环，对提供对社会至关重要的生态系统服务产生重要影响。农业可持续营养管理战略是减少这些影响、同时支持长期粮食安全和水质的关键杠杆。然而，对于农业活动和城市化如何影响生物地球化学循环（如氮、磷和碳）之间的相互作用，进而影响生态系统服务，我们的理解相对有限。另一个管理上的挑战是，我们缺乏关于这些人类对营养循环的影响如何调节特定服务的提供的机制模型。随着全球粮食需求的增加和城市化进程的继续，缩小这些与人类主导系统相关的知识差距至关重要。我的研究项目将解决这些挑战，同时训练学生进行统计和空间分析、营养预算核算和生态系统服务建模。我和我的学生的第一个目标是通过综合世界各地发表的研究数据，量化不同农业生态系统中土壤氮、磷和有机碳的比例。我们将使用这些数据来测试气候、土壤类型和农场管理在多大程度上调节土壤养分比例。其次，我们将利用假设驱动的机制模型探讨具体的养分管理策略如何影响土壤养分平衡和提供多种生态系统服务。我们的主要重点将放在农业养分使用和水质之间的关系上，包括氮磷使用比例的变化如何影响北美下游湖泊和河流的水质。第三个以城市地区为重点的目标是量化从农田到城市的养分和碳流的大小和变化。我们的模型将能够估计城市饮食中肥料的使用量，以及这如何影响当地农田根据其营养比例从城市废物流中回收营养物质的能力。这些相互关联的目标将提供新的认识，了解在人类主导的景观内部和景观之间，营养物质和碳的流动是如何紧密联系在一起的，以及农业营养管理如何成为一种机制，推动多种生态系统服务在空间和时间上的变化。我的研究计划的总体目标是帮助告知我们如何在农业集约化和城市化时代平衡竞争目标，以提高农业生产力和环境质量。我提出的研究结果将有助于推进农业和城市耦合生物地球化学循环的跨学科研究，并有可能应用于加拿大和国外的土地管理者和市政府。

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.