Virtual nitrogen and virtual water transfers embedded in food trade networks across the US

Abstract

Understanding environmental impacts through embedded resource accounting tools, such as footprints, allows scholars to connect resource demands to consumption choices. To date, considerably less attention has been paid to tracking the flow of goods, particularly at a sub-national level, to relate consumption patterns to the origin where nitrogen pollution may be occurring. We present and analyze the virtual N networks alongside virtual water networks embedded in the internal food trade within the United States. We utilize a Monte Carlo simulation to estimate the associated uncertainty of these values and compare them to existing works on both nitrogen and water footprint flows. Our results indicate that most of the US states exhibit a high nitrogen footprint for meat/seafood and a larger water footprint for cereal grain products. Additionally, we find that both the meat/seafood virtual nitrogen and virtual water networks exhibit high density and larger connectivity properties compared to the cereal grain and fruit/vegetable networks. We also examined the uncertainty associated with the commodity trade across the US and find that sampling errors tend to vary linearly with the footprint values. The sampling uncertainty in the N footprint values indicates greater variability in the cereal grain and fruit/vegetable products. To relate these networks with environmental externalities we also examined virtual N transfers between states based on the percent of assessed water bodies in a state that have nutrient-related impairments. We found that most of the virtual N transfers move from states with high impairments to states with lower rates of impairments. The outcomes from this research could be used to inform eutrophication and water use management across the United States.