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Dead Zones

Dead Zones

What is a dead zone?

“Dead zones” are areas of little to no dissolved oxygen. Most marine organisms require oxygen to survive, so marine organisms can’ survive in these areas. These dead zones typically occur in coastal waters which many coastal communities rely on as a source of food and income. In the Chesapeake Bay, the dead zone is estimated to include 11% of the total water volume of the bay in the summer months. In 2019, the Northern Gulf of Mexico dead zone measured 6,952 square miles. For reference the Gulf of Mexico is about 617,000 square miles. Dead zones have seriously impacted fisheries in the Chesapeake Bay and the Gulf of Mexico due to the commercial farming that occurs in each of their watersheds. 

Image Source: National Geographic

How are dead zones formed? 

Agricultural runoff is one of the greatest threats to marine ecosystems. The pesticides and fertilizers used in commercial agriculture are washed off of the land by rain into local waterways which eventually feed into the ocean. This runoff leads to massive “dead zones” where rivers feed into the ocean like in the Gulf of Mexico where the Mississippi meets the ocean. Dead zones form as a result of fertilizer runoff adding excess nutrients like nitrogen and phosphorus to a marine ecosystem. At first it may seem like excess nutrients would be a good thing, however it upsets the natural balance of the ecosystem and ultimately destroys it. Nitrogen and phosphorus are usually limited in marine ecosystems which limits the growth of algae. When large amounts of nitrogen and phosphorus are present as a result of runoff, algae growth is no longer limited and algae populations explode. This is called an algal bloom. 


Image Source: Smithsonian Magazine

Algal blooms can be harmful for a number of reasons including the fact that they can release noxious gases and they can cause dead zones. Dead zones are formed by algal blooms because after the algae die, they sink to the bottom to be decomposed by anaerobic bacteria. Anaerobic bacteria require dissolved oxygen, so a massive amount of dissolved oxygen is used to decompose the algae. This depletes the surrounding water of dissolved oxygen which kills marine life. In addition, algal blooms cover the surface of the water and block out sunlight from reaching aquatic plants that require it for photosynthesis, so many marine plants die as well. 

Image Source:

What can be done about it? 

One of the best ways to protect marine ecosystems from dead zones is to switch to regenerative agriculture practices that reduce fertilizer and pesticide use and control erosion. Regenerative agriculture focuses on using practices that restore soil health and improve biodiversity. Most commercial agriculture operations are large scale monocultures, meaning large areas of land are devoted to one crop, and use large amounts of fertilizers and pesticides. These practices lead to the degradation of soil and damage local biodiversity. Regenerative agricultural practices include crop rotation, planting multiple crops together as a natural form of pest control, managing erosion, and using compost. The use of these practices not only protect marine ecosystems from harmful runoff, they also improve terrestrial ecosystem biodiversity and help to build an agricultural system that is more resilient and better for the planet as a whole.

Image Source: Food Navigator 

Another way to reduce the occurrence and size of dead zones is to incorporate more seaweed into our diets. There are many different types of seaweed and many different ways it can be incorporated into our diets. Seaweed, like the kelp we use to make our chips, is a zero input crop meaning it does not require pesticides, fertilizers, land, or water. This not only saves on resources, but also does not lead to dead zones. If we can begin replacing the resource intensive crops we eat with seaweed, we can reduce the demand for some of these crops, thereby reducing their environmental impact. Seaweed also acts as a carbon sink by absorbing carbon dioxide which improves its surrounding environment.

Another important way to protect marine ecosystems from dead zones is to improve storm water management. In many places when it rains water runs straight off of crop fields and roadways or parking lots into local waterways carrying with it pesticides, fertilizers, and other chemical pollutants. This can be prevented by repairing and establishing riparian buffers around waterways. Riparian buffers are areas of native vegetation around waterways that serve to filter out pollutants and prevent them from entering the waterway. Another strategy for reducing runoff is converting impervious surfaces like pavement, concrete, and roadways to pervious surfaces that water will run through rather than run off. These include pervious concrete, pavers, and many other options. 

Image Source: Stormwater PA

Finally, legislation should be improved to better regulate agricultural runoff. Currently in the United States the major legislation that regulates water pollution is the Clean Water Act. Unfortunately, the Clean Water Act does not regulate  agricultural runoff. In order to better protect the ocean and marine organisms from the effects of water pollution, steps must be taken to address this weakness in the legislation. 


About the Author: Emma Gamble is a junior at the George Washington University majoring in Environmental Studies and minoring in public policy. Emma is passionate about incorporating greater sustainability into our food systems in order to create a greener future for people and the planet. Emma enjoys sailing, kayaking, and paddle boarding.