Nutrient Legacies and Time Lags: Understanding Catchment Hydrologic and Biogeochemical Responses in Anthropogenic Landscapes

在过去的100年里，全球人口增长了三倍多，同时土地利用发生了快速变化，农业急剧集约化。这些变化导致养分、杀虫剂和各种其他污染物在受人类影响的景观中的投入大幅增加。大多数应用的污染物最终会进入地下水和地表水，导致长期的缺氧、水生毒性和饮用水污染问题。减少化肥使用量或改变管理做法是为了改善水质，但往往不能产生预期效果。这种缺乏反应的情况可以归因于几十年来人类影响在景观中积累了遗留下来的污染物，这些污染物需要数年时间才能耗尽，并可能导致实施的最佳管理做法与观察到的水质改善之间的重大延误或时间滞后。巴苏博士的研究计划的一个基本主题是由人类影响的历史创造的这一景观遗产。了解这类遗产的积累和枯竭将有助于了解全球营养预算的基本知识，同时还可以回答决策者感兴趣的有关时间滞后的实际问题。发现号拟议的研究将建立在巴苏博士最近的工作基础上，该工作提供了有趣的新证据，表明有机氮(N)在农业景观的深层土壤中积累，特别是在密西西比河流域。这些发现提出了关于这种积累或遗产在流域尺度N动态中可能发挥的作用的重要新问题，并可能有助于解释观察到的时间滞后。因此，拟议的研究将试图回答以下问题：(1)什么机制控制农业景观中N遗产的积累和枯竭？(2)这种遗产如何导致管理做法的变化与流域水质改善之间的时间滞后？这笔赠款支持的工作将采取几条相互关联的道路来解决这些问题。这项研究将重点放在大河流域(GRW)，作为一个受农业严重影响的大流域的例子。首先，将综合20世纪中叶至今有关化肥使用、农作物和畜牧业生产以及大气氮沉积的现有数据。这样的分析将允许量化盆地内可能的遗留N家门店的规模。将进行实地采样，以通过同位素测年技术确定当前土壤N水平以及土壤有机碳(C)和N的年龄。同时，将开发一个模型，以探索关于整个土壤剖面的C-N动态的假设，并阐明N积累和消耗的主要控制因素。作为上述方法的补充，将进行受控实验室实验，以分离和量化控制N转化和运输的过程。由探索基金资助的研究将增加对人类景观中N个遗产及其对水质影响的基本了解。该项目将利用该大学在水和生态水文学领域的现有优势，促进世界级研究的卓越，并通过留住和培训顶尖HQP来为加拿大经济做出积极贡献。这项研究的结果将对流域尺度的营养物质传输和与水源保护相关的管理选择领域做出重大贡献，从而使加拿大水资源能够更有效地管理。

Global population has seen a more than threefold increase over the last 100 years, accompanied by rapid changes in land use and a dramatic intensification of agriculture. Such changes have led to large increases in the inputs of nutrients, pesticides, and a variety of other contaminants to human-impacted landscapes. The majority of applied pollutants eventually find their way into both groundwater and surface water, leading to long-term problems of hypoxia, aquatic toxicity and drinking water contamination. Reductions in fertilizer application or other changes in management practices have been implemented to achieve improvements in water quality, but often they do not yield expected results. Such lack of response can be attributed to the buildup of legacy stores of contaminants within the landscape over decades of human impact that take years to deplete and can cause significant delays or time lags between best management practices implemented and water quality improvements observed. One of the essential themes of Dr Basu's research program is this landscape legacy created by histories of human impacts. Understanding the accumulation and depletion of such legacies will contribute to a fundamental knowledge of global nutrient budgets, while also answering practical questions regarding time lags that would be of interest to policy makers. The proposed Discovery research will build on Dr. Basu’s recent work, which provides intriguing new evidence of organic nitrogen (N) accumulation in the deeper soils of agricultural landscapes, specifically in the Mississippi River Basin. These findings raise important new questions regarding the role that such accumulations, or legacy, might play in catchment-scale N dynamics, and may help to explain the observed time lags. The proposed research will therefore seek to answer the following questions: (1) What mechanisms control the accumulation and depletion of N legacies within agricultural landscapes? (2) How do such legacies contribute to time lags between changes in management practices and improvements in water quality at the catchment scale? The work supported by this grant will take several interconnected paths toward addressing these questions. The study will focus on the Grand River Watershed (GRW) as an example of a large river basin heavily impacted by agriculture. First, available data regarding fertilizer use, crop and livestock production, and atmospheric deposition of N from the mid-20th century to the present will be synthesized. Such analysis will allow the quantification of the likely magnitude of legacy N stores within the basin. Field sampling will be carried out to determine current soil N levels as well as the age of soil organic carbon (C) and N via isotope dating techniques. Concurrently, a model will be developed to explore hypotheses regarding C-N dynamics throughout the soil profile and to clarify the major controls on N accumulation and depletion. As a complement to the above approaches, controlled laboratory experiments will be carried out to isolate and quantify the processes governing N transformations and transport. Research funded through the discovery grant will increase the fundamental understanding of N legacies in anthropogenic landscapes and their impacts on water quality. The project will leverage existing strengths in the university in the areas of water and ecohydrology, promote excellence in world class research, and contribute positively to Canada’s economy by retaining and training top HQP. The results of this research will contribute significantly to the field of watershed-scale nutrient transport and management choices related to Source Water Protection, thus allowing for the more effective management of Canadian Water Resources.