Nitrogen Pollution Embedded in Commodity Supply Chains and Trade; Linking Systems and Scales across Water, Energy, and Land

Abstract:

Human alteration of nitrogen and phosphorous cycling exerts global-scale impacts on our environment, human health, water resources, and economic productivity. Despite decades of contributing billions of dollars on nutrient research and management strategies, the global community is still plagued with widespread nutrient pollution due to out-of-balance nutrient cycling. In the Chesapeake Bay, excess nitrogen has contributed to poor water quality and thus has become a focus for efforts to restore and protect the watershed. While numerous researchers continue to study nutrient transport and management in the Bay, previous work on this topic to-date has yet to carefully consider the effect of embedded nitrogen found in products imported and exported throughout the Bay.

Our work advances previous research by creating a mass flow model of nitrogen embedded in major commodity groups throughout the Chesapeake Bay linking systems across the energy, water, and land interactions. Additionally, we track the commodity flows of products in supply chains into and out of the Bay, linking systems across scales, to showcase the relationships between direct nitrogen pollution and nitrogen pollution externalities. We utilize multiple approaches to calculate embedded nitrogen including both nitrogen budget and nitrogen footprint to estimate these environmental impacts, enabling us to build a detailed picture of N fluxes at multiple scales.

The findings of this study include identification and ranking of the sources, impacted areas and spatial relationships of excess nutrients in the watershed through embedded resources and trade. The results distinguish between the direct nitrogen pollution from domestic products and the indirect pollution from outside of the bay at a regional scale. The outcome of this work showcases an integrated approach that can be applicable in different watersheds and crosses both biophysical methodology and implications for socioeconomic drivers of water pollution dynamics across food systems. The results have the potential to provide decision makers and development actors with the useful information and instruction that allows them to improve the bay water quality by supporting activities that minimize externalities across energy, food, and water resources in the Chesapeake Bay.