The most cost-effective strategy to reduce the amount of nitrogen and phosphorus flowing into the Gulf of Mexico would focus on improving practices in the Lower Mississippi sub-basin, a new Economic Research Service report says.

“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,” three of the report’s authors wrote in an article summarizing the report. “The cost of reducing nutrients delivered to the Gulf would therefore be lower in the Lower Mississippi sub-basin than on a comparable field located further upstream.”

An area of low oxygen in the Gulf of Mexico, known as the “hypoxic zone” (or “dead zone”), has been growing steadily, reaching its high of 8,776 square miles last year before falling this year to 2,720 square miles. The average size over the past years has been about 5,236 square miles.

“Continued expansion of the hypoxic zone may threaten the Gulf fishing industry and coastal economies,” the authors said.

A group of federal and state agencies making up the Mississippi River Gulf of Mexico Watershed Nutrient Task Force has set a goal of reducing the dead zone to 1,931 square miles by 2035, which would require a 45 percent reduction in nutrients entering the Gulf, scientists estimate.

“This goal cannot be met without substantial reductions in nutrient losses from agriculture, which occur through pathways such as runoff, subsurface flow, and erosion,” the authors said. In particular, “Some nutrient-reduction strategies, such as optimally placed wetlands and buffers, were found to generally be more cost effective than others within a given sub-basin.”

Inside and outside the agricultural community, the debate over how to reduce nutrients flowing to the Gulf has focused on whether voluntary or mandatory measures would be most effective. The report says one approach might be to “target financial and technical assistance to particular conservation systems, regions, or landscape characteristics where the impact of practices is estimated to be particularly high.”

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The ERS report then goes on to say that even though the Upper Mississippi “contributes the greatest share of nitrogen to the Gulf, our results suggest that the Lower Mississippi sub-basin generally has the lowest cost per unit of (nitrogen) reduction, followed by the Ohio and Tennessee sub-basins, and that cost-effective reduction efforts could be focused there.”

However, “The scale of production adjustments required to achieve a 45-percent decline in nutrient loadings across the (Mississippi/Atchafalaya River Basin, or MARB) is likely to affect commodity markets and shift some costs to purchasers of agricultural products,” the report said. “Higher estimated crop prices mitigate the costs that producers bear for implementing conservation systems.”

But higher commodity prices caused by efforts to reduce Gulf hypoxia “could increase the intensity of production and expand cropland area outside the MARB,” the report said. “Both of these outcomes result in increased nutrient and sediment loss in watersheds outside the MARB. While not large, estimated increases in nutrient and sediment loss beyond the MARB would be of concern for other regions dealing with water quality impairments.”

Attempts by Agri-Pulse to obtain comments from agriculture and conservation groups before close of business today were unsuccessful.

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