What is the Gulf of Mexico Hypoxic Zone?
The Gulf of Mexico hypoxic zone is an area along the Louisiana-Texas coast where water near the sea floor has hypoxic conditions. Hypoxia can cause fish to leave the area and can cause stress or death to bottom dwelling organisms that can’t move out of the hypoxic zone. The hypoxic zone is thought to be caused primarily by excess nitrogen delivered from the Mississippi River in combination with seasonal stratification (layering) of Gulf waters. Nitrogen promotes algal and attendant zooplankton growth. The associated organic matter, such as dead algal cells and other debris from the algae, sinks to the bottom where it decomposes, consuming available oxygen. Stratification of fresh water from the Mississippi River and saline water prevents the mixing of oxygen-rich water on the surface with oxygen-depleted water on the bottom. This lack of mixing limits the replenishment by oxygen and sustains the hypoxic zone.
