Nitrogen runoff has created a massive oxygen-deprived "dead zone" in the Gulf of Mexico, but even if the runoff was completely eliminated, it would still take at least 30 years for the area to recover, a new study estimates. Nitrogen runoff from agriculture around the Mississippi Basin has been steadily leeching into the Gulf of Mexico for decades. By 2017, the excessive nitrogen had created a "dead zone" (or hypoxic zone, where oxygen levels are extremely low and threaten marine life) in the Gulf extending 22,729 km 2 - an area larger than the state of New Jersey. A task force dedicated to studying and mitigating it was created in the early 2000s, but in spite of efforts to reduce nitrogen inputs into the Gulf, the hypoxic zone remains three times the size of these initial goals. Notably, nitrogen can move very slowly through soil and groundwater systems, meaning nitrogen runoff from agriculture can take decades to eventually reach the ocean. To explore what future targets might entail, Kimberly Van Meter and colleagues used modeling to analyze a "business-as-usual" scenario, as well as 25%, 75%, and 100% reductions in agricultural nitrogen levels. The results show that, due to earlier efforts to reduce nitrogen loads, maintaining these efforts under a business-as-usual scenario would reduce nitrogen loads by an additional 11% by 2050. However, in order to come close to achieving a reduced target hypoxic zone of 5,000 km 2 by 2050, it would be necessary to bring nitrogen levels to zero - a scenario that the authors note is "not only considered unrealistic, but also inherently unsustainable."
###
Science