Tracing Nitrogen Flows Associated with Beef Supply Chains: A Consumption-Based Assessment.

While highly connected food chains provide numerous benefits, they lack traceability and transparency. As such, understanding the spatial heterogeneity in their environmental burdens is critical for targeted interventions. This is especially important for nutrient-related impacts such as nitrogen since the release of reactive nitrogen has been linked to loss of biodiversity and decrease in water quality in different parts of the world. Animal feed production is heavily dependent on synthetic fertilizers, and the consumption of beef products, in particular, is associated with high nitrogen footprints. Although there is a rich body of work on nutrient footprints of beef production, there is a gap in understanding the spatial distribution of the nutrient releases throughout the beef supply chain in the U.S. We present an optimization-based framework to trace supply chain networks of beef products at the county level. Using publicly available data, we construct a weighted network of nutrient flows based on mass balance, including synthetic fertilizers, manure production, and crop uptake and residues. The results show that beef consumption in a county can be associated with nitrogen losses in hundreds of counties. One year worth of beef consumption in the United States released approximately 1.33 teragrams (Tg) of N to the environment, and most of it as diffuse pollution during the feed production phase. Analysis also revealed the huge disparity between consumption-based and production-based impacts of beef and the need for considering consumption-based accounting in discourse around the environmental sustainability of food systems.

Consumption-Based Accounting for Tracing Virtual Water Flows Associated with Beef Supply Chains in the United States.

Enhancing the environmental sustainability of food systems requires an understanding of both production- and consumption-based impacts. As food supply chains become increasingly complex and connected, they also present a unique context in which to understand the environmental impacts of consumption. This is critical for understanding the disconnect between production- and consumption-based impacts of food systems and ultimately designing, evaluating, and implementing interventions for improving security, resilience, and sustainability of food systems. Using publicly available datasets and an optimization-based framework, we present a county-to-county level network model of beef supply chains in the United States. The model is used to connect and attribute the consumption-based impacts of beef consumption to production in distant locations, specifically focusing on water-based impacts. We specifically focus on the beef system because of its importance in the diet of U.S. consumers and in environmental sustainability discourse. The findings from this work show the spatial disconnect between the consumption and production counties with approximately 22 billion m3 of blue virtual water being transferred for the year 2017, mainly from the northern and southern plains toward the coasts. These results highlight the importance of understanding environmental impacts from both production and consumption perspectives.