The 2019 Gulf of Mexico “Dead Zone” is predicted to be the second-largest on record. A dead-zone is an area of very low oxygen (hypoxia) where most life cannot survive. A major cause of the Dead Zone is nitrogen and phosphorous fertilizer runoff from field agriculture along the Mississippi River. This year’s zone was exacerbated by higher-than-usual rainfall.
Aquaponic systems are “closed-loop”; growers carefully manage nutrients and water discharges. By growing with more aquaponics we can limit the fertilizer that enters the Gulf and reduce future dead zones.
Carleton College provides some good background information about the Gulf Dead Zone: "The Gulf of Mexico dead zone is an area of hypoxic (less than 2 ppm dissolved oxygen) waters at the mouth of the Mississippi River. Its area varies in size, but can cover up to 6,000-7,000 square miles.
“The dead zone is caused by nutrient enrichment from the Mississippi River, particularly nitrogen and phosphorous. Watersheds within the Mississippi River Basin drain much of the United States, from Montana to Pennsylvania and extending southward along the Mississippi River. Most of the nitrogen input comes from major farming states in the Mississippi River Valley, including Minnesota, Iowa, Illinois, Wisconsin, Missouri, Tennessee, Arkansas, Mississippi, and Louisiana. Nitrogen and phosphorous enter the river through upstream runoff of fertilizers, soil erosion, animal wastes, and sewage. In a natural system, these nutrients aren’t significant factors in algae growth because they are depleted in the soil by plants. However, with anthropogenically increased nitrogen and phosphorus input, algae growth is no longer limited. Consequently, algal blooms develop, the food chain is altered, and dissolved oxygen in the area is depleted. The size of the dead zone fluctuates seasonally, as it is exacerbated by farming practices. It is also affected by weather events such as flooding and hurricanes.
“Nutrient overloading and algal blooms lead to eutrophication, which has been shown to reduce benthic biomass and biodiversity. Hypoxic water supports fewer organisms and has been linked to massive fish kills in the Black Sea and Gulf of Mexico.
“The Gulf of Mexico is a major source area for the seafood industry. The Gulf supplies 72% of U.S. harvested shrimp, 66% of harvested oysters, and 16% of commercial fish (Potash and Phosphate Institutes of the U.S. and Canada, 1999). Consequently, if the hypoxic zone continues or worsens, fishermen and coastal state economies will be greatly impacted.
Sources: Carlton College and The Aquaponics Association