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The
Dead Zone
At the southern edge of Louisiana, the Mississippi River drains
into the Gulf of Mexico and brings death. Fish and other sea life cannot
survive in this area. Spreading 7000 square miles from the foot of the
Mississippi River is an area known as the Dead Zone, or Hypoxic Zone.
Hypoxia is when water has little to no dissolved oxygen in it. Many marine
creatures breathe oxygen, just like you and I do. Low oxygen levels generally
begin in the spring, due to high nutrient levels in the Mississippi and
its tributaries.
Here's what happens: In the spring, farmers put fertilizer on their fields,
to increase the rate at which their plants grow. Many row crops like corn,
and soybeans, need nutrients like nitrogen to grow. But, when the spring
rains come, those same nutrients wash off the fields, and run right into
the rivers. The huge amount of nutrients in the rivers are eaten by phytoplankton,
a tiny aquatic plant. With all that food, the phytoplankton population
blooms! When these phytoplankton die, they sink to the bottom of the river,
where bacteria eat them and break them down. Again, with all that food
for the bacteria to consume, the bacteria multiply, and consume the oxygen
in the water faster than it can be replenished. Because the bacteria have
used up all the oxygen, the local fish and other oxygen breathers must
leave the area, or suffocate.
One count puts nitrogen based fertilizer use in the Mississippi River
basin at 6.6 million metric tons per year. That's a lot of fertilizer,
and it drains off the land into the Mississippi River from all the tributaries.
This extra nitrogen running off of fields accounts for more than half
of the river's nitrogen input for a year. The other major contributor
is animal manure, at twenty five percent of the river's annual nitrogen.
It seems that the simple answer would be to cut down the use of nitrogen-based
fertilizers in the Mississippi River basin. But, here's the tricky part-
there are no simple answers. Farms use the fertilizer to produce the crops
that feed you and me, the nation, and the world. Is there some other way
they could reduce the amount of nitrogen running off into the Mississippi
River, without contributing to the Dead Zone in the Gulf of Mexico? Lots
of people are looking for answers to that question.
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