Impacts of future scenarios on the nitrogen loss from agricultural supply chains in the Chesapeake Bay

Excessive nitrogen (N) pollution in the Chesapeake Bay is threatening ecological health. This study presents a multilayer N flow network model where each network layer represents a stage in the production step from raw agricultural commodities such as corn to final products such as packaged meat. We use this model to assess the impacts of alternative future agricultural production and land use changes on multiple pathways of N pollution within the Chesapeake Bay Watershed (CBW). We analyzed N loss via all pathways under multiple future scenarios, considering crop-specific projections based on empirical data and US Department of Agriculture projections. We found two model parameters, fertilizer nitrogen application rate (FNAR) and feed conversion ratio (FCR), to be particularly important for seeing measurable N loss reductions in the Bay. Our results indicate a large increase in N loss under the business-as-usual trajectory in geographic locations with intensive agricultural production. We found that numerous management scenarios including improvements in FNAR and FCR, N losses fall short of the 25% total maximum daily load targets. Our work suggests that achieving the CBW N loss reduction goals will necessitate large deviations from business as usual. Our model also highlights substantial regional variations in nitrogen loss across the U.S., with central regions like the Corn Belt and Central Valley of California experiencing the highest losses from crop-related stages, while eastern areas such as the Chesapeake Bay exhibit major losses from live animal production, underscoring the need for region-specific management strategies. Thus, implementation of effective N management strategies, combined with improved crop residue management, remains pivotal in mitigating N pollution in the Chesapeake Bay.