Reducing nitrogen export from the corn belt to the Gulf of Mexico: Agricultural strategies for remediating hypoxia

Authors: MCLELLAN, EILEEN - Environmental Defense; ROBERTSON, DALE - Us Geological Survey (USGS); SCHILLING, KEITH - Iowa Geological Survey; Tomer, Mark; KOSTEL, JILL - Wetlands Research Centre; Smith, Douglas; King, Kevin

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/17/2014
Publication Date: 10/15/2014
Citation: McLellan, E., Robertson, D., Schilling, K., Tomer, M.D., Kostel, J., Smith, D.R., King, K.W. 2014. Reducing nitrogen export from the corn belt to the Gulf of Mexico: Agricultural strategies for remediating hypoxia. Journal of the American Water Resources Association. 51(1):263-289. https://doi.org/10.1111/jawr.12246.
DOI: https://doi.org/10.1111/jawr.12246

Interpretive Summary: Recently, a goal of a 45% decrease in the amount of nitrogen reaching the Gulf of Mexico has been set to avoid hypoxia. This goal can only be achieved through strict targeting of nitrogen sources in agricultural landscapes. The objectives of this work were to determine the extent and types of practices, as modeled by the USGS SPARROW model, to achieve the 45% decrease in nitrogen loading to the Gulf of Mexico. From this work, in-field nitrogen management (i.e. use of cover crops and adaptive management for nitrogen) can only reduce nitrogen loads by 25%. Therefore, the in-field practices need to be coupled with downstream nitrogen removal practices, such as tile-drainage treatment wetlands, stream restoration of floodplain reconnection. By coupling in-field practices with downstream practices (estimated to require taking 1% of agricultural land out of production), the goal of a 45% decrease in nitrogen loads to the Gulf of Mexico can be achieved. This work serves to begin discussions between policy makers, conservationists and agricultural producers toward developing a working strategy that will decrease nitrogen loading from the Corn Belt and improve the ecological integrity of the Gulf of Mexico.

Technical Abstract: We used the SPARROW model for the Upper Mississippi River Basin to evaluate the potential water quality benefits (nutrient load reductions) likely to be achieved by a variety of agricultural conservation practices in the Upper Mississippi-Ohio River system, and to compare these to the 45% nitrogen load reduction needed to remediate hypoxia in the Gulf of Mexico (GoM). Our results suggest that in-field nitrogen management practices (cover crops and nitrogen adaptive management) can produce only a 25% decrease in nitrogen loading under even the most optimistic of scenarios. The goal of a 45% decrease in loads to the GoM can only be achieved through coupling of these in-field practices (cover crops and more judicious use of fertilizers) with downstream nitrogen removal practices such as tile-drainage treatment wetlands, drainage ditch enhancements, stream restoration and floodplain reconnection. Combining traditional field-scale conservation practices with downstream nutrient removal practices offers an opportunity to dramatically reduce nutrient export from agricultural landscapes while minimizing impacts to agricultural production: meeting the 45% goal required taking less than 1% of Basin cropland out of production. Conservationists, policy makers and agricultural producers seeking a workable strategy to reduce nitrogen loading from the Corn Belt will need to employ a mix of existing and more innovative conservation practices strategically placed across the landscape.