Magnitude and trends of nitrogen and phosphorus inputs, outputs, and surplus to the Mississippi/Atchafalaya River Basin (MARB) - Presentation to HTF CC

EPA ORD was asked by OW to provide information about nutrient inputs to the Mississippi/Atchafalaya River Basin (MARB) that would be included in the 2025 Hypoxia Task Force Report to Congress.  EPA’s National Nutrient Inventory presents a compilation of datasets from nationally quantified nitrogen (N) and phosphorus (P) inputs at county, state and HUC8 scales (Sabo et al. 2019, 2021 a, b).  The spatial and temporal trends of these anthropogenic N and P inputs to the MARB can be assessed using this data, with anthropogenic defined as inputs from agricultural, atmospheric (N only) and human waste sources.  Agricultural N sources include atmospheric deposition, livestock manure, synthetic farm fertilizers and biological N fixation on cropland, and account for 81% of anthropogenic N inputs to the MARB in 2017.  sources of livestock manure and farm fertilizer account for 97% of P inputs in 2017.  Between 1987-2017, agricultural N sources increased by 7.3 million tons or by 46%, and agricultural P sources increased by 0.67 million tons or by 32%. These increases in inputs were offset by a 66% and 71% increase in N and P removal in crop harvest, respectively, resulting in little change in N and P surplus over the same 30-year period.  

Impact/Purpose

Background: EPA ORD was asked by OW to provide information about nutrient inputs to the Mississippi/Atchafalaya River Basin (MARB) that would be included in the 2025 Hypoxia Task Force Report to Congress.  EPA’s National Nutrient Inventory presents a compilation of datasets from nationally quantified nitrogen (N) and phosphorus (P) inputs at county, state and HUC8 scales (Sabo et al. 2019, 2021 a, b).  The spatial and temporal trends of these anthropogenic N and P inputs to the MARB can be assessed using this data, with anthropogenic defined as inputs from agricultural, atmospheric (N only) and human waste sources. Summary of Findings:  Agricultural N sources include atmospheric deposition, livestock manure, synthetic farm fertilizers and biological N fixation on cropland, and account for 81% of anthropogenic N inputs to the MARB in 2017.  sources of livestock manure and farm fertilizer account for 97% of P inputs in 2017.  Between 1987-2017, agricultural N sources increased by 7.3 million tons or by 46%, and agricultural P sources increased by 0.67 million tons or by 32%. These increases in inputs were offset by a 66% and 71% increase in N and P removal in crop harvest, respectively, resulting in little change in N and P surplus over the same 30-year period.  Impact:  These trends of improved nutrient use efficiency and stable surplus may indicate progress toward reducing nutrients available for export across the basin.  These are new data not currently included in the HTF progress tracking metrics and represent useful information that will allow the stakeholders to see the changes in terrestrial inputs, surplus and crop nutrient use across the basin.  Coordination with OW:  This information was requested to be presented to the Hypoxia Task Force Coordinating Committee by OW, and we have worked closely with OW’s Katie Flahive, the Hypoxia Task Force Coordinating Committee Co-Chair, to define terms clearly, present the data in an understandable way to stakeholders, and clarify the message and findings. 

Citation

Markley, S., M. Brehob, M. Weber, R. Sabo, M. Pennino, R. Hill, S. Alford, AND J. Compton. Magnitude and trends of nitrogen and phosphorus inputs, outputs, and surplus to the Mississippi/Atchafalaya River Basin (MARB) - Presentation to HTF CC. Hypoxia Task Force Coordinating Committee Virtual Meeting, Virtual by OW in DC, DC, April 03, 2025.