Wherever people live, land is disturbed for
building and fertilized for farming. Rain washes the disturbed soil, farm
fertilizer and animal waste into waterways, almost all of which eventually lead
to the ocean.
This runoff along with human waste water (sewage) fertilizes the oceans, and creates large blooms of algae and other tiny marine organisms. When they die and decompose, the process consumes large amounts of oxygen in the water. That means there’s very little oxygen left and most other organisms essentially suffocate.
Wherever this happens, it’s called a “dead zone.” The term isn’t totally accurate, because all the living organisms don’t completely die. . . usually. A better term is a “hypoxic zone” which means “oxygen deficient.” Many fish can swim away from a hypoxic zone into healthier waters, but bottom dwelling animals such as oysters, clams and corals cannot. Insufficient oxygen stresses organisms that are trapped in the hypoxic zones, killing them or making it hard for them to reproduce. Their numbers dwindle, and sometimes, hypoxic zones can in fact become true dead zones that look like underwater deserts.
Gulf of Mexico Dead Zone
Nutrients flowing into the Gulf of Mexico from the Mississippi River have caused a huge hypoxic Zone larger than the state of Pennsylvania. It’s more than 7,000 square miles.
But “dead zones” can be brought back to life. The Black Sea dead zone was once the largest known hypoxic zone in the world, but it nearly disappeared between 1991 and 2001. During that time period, an economic crisis in that part of the world led to a halt in fertilizer use.
What Can You Do? Stop Runoff
- Rake your leaves and keep them out of the storm drains (they decay and send nutrients right into waterways.
- Stop fertilizer and waste runoff—If you or someone in your family manage a lawn or garden, learn about runoff and try to eliminate it.
- Use rain barrels to capture rain water so it doesn’t flow over land and run into waterways.