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Gulf Hypoxia

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The "dead zone" off the coast of Louisiana and Texas in the Gulf of Mexico is thought to be at its largest size on record. But what is this dead zone, and what does it have to do with Indiana?

Gulf Hypoxia: What is It and How are We to Blame?

The scientific word for the commonly named "dead zone" is hypoxia, or low oxygen. The lack of oxygen in these waters creates an area where marine life must struggle to survive if they survive at all. Out of all the coastal waters exhibiting hypoxia, the Gulf of Mexico is the second largest in the world. Several factors cause this phenomenon, but the water drained from the Mississippi River into the Gulf is primarily to blame.

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A combination of physical, chemical and biological factors creates the conditions that result in hypoxia. During most of the year, oxygen-rich water reaches the bottom. However, in late spring and summer, the surface and bottom waters of the Gulf stratify into two layers. Warm, less dense freshwater from the Mississippi and Atchafalaya rivers spreads out on the surface of the colder Gulf water. The calm sea winds and warm temperatures prevent the layers from mixing thoroughly and circulating oxygen throughout the waters. Hypoxia is a natural process that happens every late spring through late summer. So why is the Mississippi River and its large watershed to blame?

The Mississippi drains 41% of North America (31 states - Indiana included - and two Canadian provinces) into the Gulf of Mexico. Along with water, the river introduces tons of sediment and nutrients to the sea. These nutrients come from agricultural, industrial and urban runoff. Fertilizers, cattle farms and wastewater treatment facilities are just a few factors contributing to the incredibly high nutrient levels. While the Gulf relies on nutrients such as nitrogen and phosphorus to stimulate marine life growth, too much of a good thing can be deadly. 

Microscopic algae, or phytoplankton, use the abundance of nutrients to reproduce. Eventually their populations explode causing a plankton or algae bloom. When the plankton die, they sink to the bottom and decompose. The slow decay uses oxygen, depleting the oxygen living organisms at the bottom need and causing the water to become hypoxic - having less than two milligrams of dissolved oxygen per liter. All marine life is threatened; those that can leave do while resident species become stressed and eventually die. 

Though it was predicted to be the largest area of hypoxia to date (2008), the Louisiana Universities Marine Consortium has documented the final size of the Gulf hypoxia at 8,000 square miles. Though not the biggest - 2002's Gulf hypoxia registered at 8,841 square miles - there were many reasons why many oceanic organizations believed it would top the record. The Midwest/Mississippi River flooding and the large influx of nitrogen due to increased agriculture production were the main factors as to why such a prediction was made. Fortunately this kind of record shouldn't be broken and steps can be taken by those who live in the Mississippi River's watershed to ensure that it doesn't in the future.

What We Can Do in Indiana to Lessen our Impact on Gulf Hypoxia

Though Gulf hypoxia does not directly affect our economy as it does to Louisiana or Texas, we do directly contribute to the dead zone by the way we manage our lands. It's important to remember that everybody is downstream of someone else. What we do to our water and land will impact those around us. Good stewardship is the only way we Hoosiers can lessen our impact on Gulf hypoxia.

The problem stems from both agricultural and urban run-off. Farmers use phosphorus and nitrates to grow their crops, which eventually find their way to the Mississippi River. Growing cities means more land under concrete and less soil for polluted water to soak into instead of becoming runoff. This summer, we've learned that our state needs to instill better, more efficient flood control practices. All these factors that have contributed to the dead zone can fortunately be fixed or improved.

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The Nature Conservancy has identified a set of actions that could contribute to the reduction of the hypoxia zone. By restoring wetlands and riparian systems to capture nutrients and reduce these inputs at the source, the Conservancy’s Gulf of Mexico Initiative and the Mississippi River Program and our partners are aiming to slow or even reduce the growth of this hypoxic zone and its effects throughout the region. The Nature Conservancy in Indiana also works to improve situations in our own state by helping farmers build two-stage drainage ditches, and restoring wetlands and forests near our waterways.  A half-mile two-stage drainage ditch removes 53 tons of nitrogen per year . That's the equivalent of 17 elephants!

Hoosiers can help by being greener when it comes to their home and lawn. By following these eco-friendly water tips, you too can help decrease Indiana's impact on the Gulf of Mexico's hypoxic zone.

  • Use environmentally friendly landscaping techniques that require less fertilizer, prevent erosion, and use native plants. Using a soil test kit will help you determine the amount of fertilizer you actually need.
  • Leave grass clippings on the lawn to recycle nutrients or start a compost pile to reduce the amount of waste you put into the garbage disposal or garbage can.
  • Conserve water at home to reduce the volume of wastewater that must be treated by a sewage treatment plant or septic system. This will increase the efficiency of treatment and save you money.
  • Use safe, non-toxic alternatives for cleaning and for controlling pests. Always take your household/lawn chemicals to a recycling center, not in the trash or down your drain.
  • Wash your car on a grassy area if possible, so the ground can filter the water naturally. Use soap sparingly and try to use nonphosphate detergents. Empty the bucket of soapy water down the sink, not in the street.
For More Information

EPA's Mississippi Basin & Gulf of Mexico Hypoxia

USGS - Hypoxia in the Gulf of Mexico

National Oceanic & Atmospheric Administration final integrated assessment on Hypoxia


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