PS 31-14 - Towards an integrated nitrogen and phosphorus footprint tool for consumers in the United States

Wednesday, August 9, 2017
Exhibit Hall, Oregon Convention Center
Rebecca L. Clarke1, Genevieve S. Metson2, Allison M. Leach3, Graham K. MacDonald4, Jana E. Compton5, Jennifer Andrews6, Elizabeth Castner7, James N. Galloway7 and Tim R. Moore8, (1)Washington State University, (2)School of the Environment, Washington State University Vancouver, WA, (3)Natural Resource and Earth Systems Science and The Sustainability Institute, University of New Hampshire, Durham, NH, (4)Geography, McGill University, Montreal, QC, Canada, (5)US EPA, NHEERL, Western Ecology Division, Corvallis, OR, (6)Sustainability Institute, University of New Hampshire, (7)University of Virginia, (8)Geography and Global Environmental & Climate Change Centre, McGill University, Montreal, QC, Canada

Human activity has fundamentally altered the global nitrogen (N) and phosphorus (P) cycles—even more profoundly than the carbon cycle—leading to massive environmental consequences. Although P is necessary for food production, excess P leads to environmental consequences, such as eutrophication and harmful algal blooms, which can influence recreation, transportation, fisheries, human health and water treatment costs. Nutrient stoichiometry (N:P) can play an important role in regulating ecosystem function, and the N:P associated with agricultural inputs, processing losses and waste warrants further attention. An integrated perspective on the release of both elements to the environment from human actions would allow for a better understanding of the management of these drivers in concert. In this project, we developed virtual P factors, which describe the P lost to the environment during the food production process for major food categories in the United States. The methods match those of existing virtual N factors. The virtual P factors will contribute to the creation of an integrated N and P footprint tool to help consumers understand and reduce their contribution to N and P pollution.


Virtual P factors (VPF), as may be expected by stoichiometric relationships, were smaller than virtual N factors (VNF). For example, corn has a VPF of 2.7 g P / kg food and a VNF of 15 g N / kg food. We found that like with the N footprint, the consumption of animal products in US diets has a disproportionately large impact on an individual’s P footprint. In fact dietary choices, specifically the consumption of meat, contributes to the majority of an individual’s P footprint and represents a larger faction of the P footprint than N footprint. For N footprints, in part because of N emissions related to fossil fuel combustion, travel decisions and energy consumption can be used as leverage points for change, but this is not the case of P because negligible amounts of P are emitted from fossil fuel combustion. In summary, individual U.S. consumer integrated N and P footprints can inform the public about ways to decrease their environmental impact linked to nutrient losses. Importantly, this combined N-P footprint tool will facilitate future work to integrate with existing carbon accounting tools.