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

点击翻译按钮获取中文摘要

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.