The most cost-effective strategy to reduce the Gulf of Mexico hypoxia zone would be to focus on implementing nutrient reduction practices in the Lower Mississippi sub-basin rather than Iowa or other upstream states, according to a new Economic Research Service report.

“The Lower Mississippi sub-basin’s proximity to the Gulf means that a higher percentage of nutrient losses from fields would reach the Gulf from the Lower Mississippi than from cropland further upstream,” the report’s authors wrote. “The cost of reducing...