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Legacy nitrogen may prevent achievement of water quality goals in the Gulf of Mexico

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Science  22 Mar 2018:
eaar4462
DOI: 10.1126/science.aar4462

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Abstract

In August 2017, the Gulf of Mexico’s hypoxic zone was declared to be the largest ever measured. It has been estimated that a 60% decrease in watershed nitrogen (N) loading may be necessary to adequately reduce eutrophication in the Gulf. However, there has been no rigorous assessment of the impact of N legacies on achieving water quality goals. Here we show that even if agricultural N use became 100% efficient, it would take decades to meet target N loads due to legacy N within the Mississippi River Basin. Our results suggest that both long-term commitment and large-scale changes in agricultural management practices will be necessary to decrease Mississippi N loads and to meet current goals for reducing the size of the Gulf hypoxic zone.

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