Negli ultimi 5 anni la National Oceanic and Atmospheric Administration (NOAA) ha annunciato il record (2017) e valori al di sopra della media (2019 e 2021) per quanto riguarda l’estensione della zona morta del Golfo del Messico. Ruairí Arrieta-Kenna su Vox parla del record di estensione del 2017:

The National Oceanic and Atmospheric Administration (NOAA) announced Wednesday [Agosto 2017] that this year’s “dead zone” in the Gulf of Mexico is the largest ever measured.

Stretching from the coast of Louisiana at the Mississippi River Delta westward to the shores of Texas, the area of severe hypoxia — when the water is so depleted of oxygen that it can’t sustain fish and marine life — encompasses 8,776 square miles. That’s roughly the size of New Jersey (or more than 4 million football fields, if that’s any easier to grasp). […]

The dead zone in the Gulf has become a worrisome annual phenomenon mainly due to excess nitrogen and other nutrients that run off from rivers like the Mississippi into the Gulf and feed the growth of algae. When the massive blooms of algae and phytoplankton die, their decomposition consumes all the oxygen in the ocean, creating a hypoxic area, or dead zone. Fish that can swim away do, but the organisms that can’t, including the plants that fish feed on, die. […]

Don Scavia, a professor at the University of Michigan and former top scientist at NOAA, wrote in a blog post: “In spite of more than 30 years of research and monitoring, over 15 years of assessments and goal-setting, and over US$30 billion in federal conservation
funding since 1995, average nitrogen levels in the Mississippi have not declined since the 1980s.”

Le dimensioni medie della zona morta sono ancora molto lontane dal valore che si è prefissata di raggiungere la Hypoxia Task Force (HTF goal), come riporta Associated Press:

Over the past five years, the average size of the low-oxygen, or hypoxic, zone has been 5,380 square miles (13,934 square kilometers). That’s 2.8 times larger than the goal set by a federal task force to reduce the five-year average to 1,900 square miles (4,921 square kilometers) or smaller by 2035.

Because year-to-year measurements can vary widely — this year’s zone is about three times the size of 2020’s — NOAA says a multiyear average “captures the true dynamic nature of the zone.”

Il Guardian parla del fatto che saranno necessari almeno 30 anni per riportare la Costa del Golfo ad una condizione non eutrofica:

The enormous “dead zone” in the Gulf of Mexico will take decades to recover even if the flow of farming chemicals that is causing the damage is completely halted, new research has warned.

A parte le oscillazioni di anno in anno, dovute a vari fenomeni atmosferici quali piogge intense e tifoni, l’aumento delle dimensioni della zona morta della Costa del Golfo e’ dovuto alle grandi quantità di nutrienti (nitrati e fosfati) riversati nell’oceano dal fiume Mississippi, anche se la discussione sui principali colpevoli e’ molto accesa. Agricoltura e allevamento (e in generale le nonpoint sources, che includono anche l’inquinamento atmosferico) contribuiscono all’eutrofizzazione a causa del trasporto di fertilizzanti sintetici e naturali dai terreni agricoli alle acque del Golfo del Messico. Alcuni attivisti accusano le aziende produttrici carne di essere i maggiori responsabili della zona morta nella Costa del Golfo, la quale, a sua volta, ha conseguenze sulla filiera del pesce, come riporta Vox:

Hypoxia hurts the Gulf of Mexico’s commercial and recreational fishing industries, which are still recovering from recent hurricanes and oil spills. The Gulf produces more than 40 percent of the nation’s domestic seafood supply and, according to the EDF, generates billions of dollars a year in wages for the fishing and tourism industries across five states. An NOAA-funded study by Duke University found that hypoxia in the Gulf in particular drives up the prices of large shrimp, creating an economic ripple effect on seafood markets and consumers.