Citation:

Metson, G., G. MacDonald, A. Leach, J. Compton, J. Harrison, AND J. Galloway. The U.S. consumer phosphorus footprint: where do nitrogen and phosphorus diverge? Environmental Research Letters. IOP Publishing LIMITED, Bristol, Uk, 15:105022, (2020). https://doi.org/10.1088/1748-9326/aba781

Impact/Purpose:

EPA scientist Jana Compton worked with faculty members in Sweden, the US and Canada to develop a phosphorus footprint for U.S. consumers that parallels the approach already established for nitrogen. They present a novel quantitative picture of the phosphorus released associated with US consumers, and compare how the production of different food items, and waste management results in different nitrogen to phosphorus ratios. These ratios in turn have implications for water quality, because eutrophication is affected not only by total nutrient addition but also stoichiometry. This work builds on the footprint methodology put forward for nitrogen by some of our co-authors. This work was supported by an SHC supported NRC fellowship to Genevieve Metson, and also SHC support in a cooperative agreement with the University of Virginia. The authors plan to submit this paper to a special issue titled “Focus on Environmental Footprint Tools for Sustainability” in Environmental Research Letters.

Description:

Phosphorus (P) and nitrogen (N) are essential nutrients for food production but their excess use in agriculture can have major social costs, particularly related to water quality degradation. Nutrient footprint approaches estimate N and P release to the environment through food production and waste management and enable linking these emissions to particular consumption patterns. Following an established method for quantifying a consumer-oriented N footprint for the United States (U.S.), we create an analogous P footprint and assess the N:P ratio across different stages of food production and consumption. Circa 2012, the average consumer’s P footprint was 4.3 kg P capita-1 yr-1 compared to 22.4 kg N capita-1 yr-1 for the food portion of the N footprint. Animal products have the largest contribution to both footprints, comprising >70% of the average per capita N and P footprints. The N:P ratio of environmental release based on virtual nutrient factors (kilograms N or P per kilogram of food consumed) varies considerably across food groups and stages. The overall N:P ratio of the footprints was lower (5.2 by mass) than for that of U.S. food consumption (8.6), suggesting that P is managed less efficiently than N in food production systems but more efficiently removed from sewage. While strategies like reducing meat consumption will effectively reduce both N and P footprints by decreasing overall synthetic fertilizer nutrient demands, nutrient management interventions should also consider how food production and waste treatment differentially affect N and P releases to the environment in order to better manage eutrophication.

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