The dead zone in the Northern Gulf of Mexico did not reach its record-setting prediction this year, but scientists are still concerned that the measurement may not paint the full picture of the problem.

The dead zone begins where the Mississippi River mixes with the Gulf of Mexico. The Mississippi serves as a drain for 32 U.S. states and two Canadian provinces. Fertilizer from crop farms in the Midwest washes off the soil and drains into the river where it mixes with urban wastewater. When this nutrient-rich water reaches the Gulf of Mexico at the mouth of the Mississippi, it creates an ideal environment for algae blooms.

As the algae die and decompose, they use up much of the oxygen in the water and create a hypoxic area, or as it’s more commonly known, a dead zone. Most creatures cannot survive within this oxygen-starved environment, so many species either die or are displaced in search of a more sustainable habitat.

In response to this pressing concern, the EPA created the Mississippi River/Gulf of Mexico Hypoxia Task Force, a partnership between 12 federal and state agencies and the National Tribal Water Council to study its cause and effects and reduce its size, severity and duration.

This year, researchers predicted that the area’s seasonal dead zone would be one of the largest on record, approximately the size of Massachusetts. The measurement obtained in July was smaller than projected, but researchers suggest that might be due to Hurricane Barry. The winds from a hurricane can mix up the water column, spreading out the low-oxygen water and introducing water with higher levels of dissolved oxygen. Since the measurement came a little over a week after Hurricane Barry, they claim that the area may not represent its true scale.
Despite not reaching original predictions at the time of measurement, the 6,952-square-mile area was still the eight largest ever recorded.

While the dead zone in the Gulf is a seasonal occurrence in the summer, the trends are worrying.

Climate change is exacerbating the issue

A changing climate also means a change in the frequency of storms and a lengthening of the warm seasons in which the hypoxia in the Gulf peaks. Climate models predict more rain for future spring seasons in the Midwest. The storms could result in more soil erosion, with an increase in nutrient runoff as delayed planting reduces the amount of crop cover to keep the soil in place.

Additionally, hypoxic zones lower the pH of the water as a result of CO2 produced by the phytoplankton, adding to the global concern over ocean acidification. In fact, a recent study links dead zones with the problem of ocean acidification.

Unless major change is enacted, the outlook is not good for meeting the Hypoxia Task Force’s target size for the area. This year’s dead zone exceeded the 5-year average and has been above the target level in all but one year since 1990 (*only 2000 was below; 2016 has no data available).

Effects of the Dead Zone

While the total area measured was smaller than predicted, many are still feeling its effects.

The hypoxic zone is not just an issue for researchers and environmental agencies. In several Gulf fisheries, species are often forced to relocate to more oxygen-rich waters. Fishing fleets often must relocate with them to make their living. Certain species, however, are more affected by the oxygen-poor conditions than others.

One example is the brown shrimp. For fishermen in the Gulf, brown shrimp represent one of the most important catches. Due to the relocations, however, the shrimp move closer inland, and fleets follow, preventing them from reaching deeper waters that allow them to grow to their full size. This affects not only the population, but also the economic benefit of the catch. Smaller sizes do not earn as much as larger shrimp.

As a result of mostly voluntary measures to curb nutrient pollution and higher than average rainfall, the dead zone continues to increase in size. This increase in rainfall compounds the effect the dead zone has on fisheries. The increased water volume of the Mississippi has led officials to keep the Bonnet Carre Spillway open much longer than normal, draining the excess water into Lake Pontchartrain to prevent flooding. The increased amount of fresh water pouring into the brackish estuary negatively impacts the environment. Oyster and crab populations have taken a major hit, prompting lawmakers and representatives from the Louisiana Shrimp Association to appeal for a state of emergency declaration.

Aerial image of the Bonnet Carre Spillway
The Bonnet Carre Spillway. Image courtesy of NASA Earth Observatory


This increase in fresh water may also have played a role in an unusually high amount of dolphin deaths in the Gulf. Bottlenose dolphins who live near the dead zone have been dying at three times the normal rate. In fact, the number of dolphin deaths is higher than at the height of the Deepwater Horizon Spill. Although the cause of the high death rate is unknown, it is possible that in following displaced prey closer inland, the dolphins are exposed to fresh water which makes them more susceptible to disease. Dolphins have washed up on Gulf Coast beaches with lesions on their skin, usually a symptom of freshwater exposure.

The outlook of the situation is bleak. With around 40% of the country draining urban wastewater and farmland runoff into the Mississippi River watershed, a large-scale change is needed most where the effects of the nutrient pollution are not immediately felt.

For some, that change isn’t coming fast enough. The Advocate describes Thomas Olander, the Louisiana Shrimp Association chair, urging his son to be the first of four generations to not work in the family shrimping business.

Fisheries in the Gulf of Mexico net the third-largest seafood revenue in the United States at over $912 million. The Gulf also accounts for more than $23 billion in sales and generates 137,000 jobs in western Florida alone.

How Can You Help

The most important step you can take is to support legislation that aims to curb nutrient pollution.

With much of the corn production from the Midwest going to feed cattle or produce ethanol, scientists suggest reducing your consumption of meat and corn and support investment in alternative energies.

To learn more about the Gulf dead zone, click here: