KNOWLEDGE YOU CAN USE

KNOWLEDGE YOU CAN USE
Life in the Dead Zone: In boosting plant productivity on farms, we’ve created a “dead zone” in the Gulf of Mexico bigger than Connecticut.

In the water at the mouth of the Mississippi River, each spring and summer, there is so little oxygen that virtually no life can survive.

Question 15.14

Q: Which chemical almost always limits plant growth? Plant growth requires the production of proteins, all of which contain nitrogen. Access to nitrogen nearly always determines how much a plant grows.

Question 15.15

Q: If you’re a farmer, how can you increase the productivity of your crops? Add nitrogen. This, in fact, is the chief component of all plant fertilizers.

Question 15.16

Q: Where does the unused nitrogen end up? Spring and summer rains wash nutrients, dissolved organic materials, and other runoff (much of which comes from human sources) from the middle of the United States into nearby rivers and thus, eventually, into the Mississippi River. From there they flow into the Gulf of Mexico.

Question 15.17

Q: What happens when large amounts of nitrogen are dumped into a body of water? Organisms such as plankton and algae living near the mouth of the Mississippi grow like crazy with all the extra nitrogen and nutrients that are washed into the Gulf of Mexico. But their rapid increase in productivity disrupts the food chain as they decay, increasing the organic matter that sinks to the bottom and feeds the bacteria there. As the bacteria thrive, they consume ever-increasing amounts of oxygen.

Question 15.18

Q: What happens when bacteria use up too much oxygen? Excessive bacterial growth depletes the supply of dissolved oxygen in the water, starving all other life of oxygen—including fish, crabs, oysters, and shrimp, all of which die or move out of the area. This creates a “dead zone” and ruins local fisheries, with a significant impact on the economies they support.

Question 15.19

Q: What can you conclude? Disrupting food chains, even increasing the productivity of certain trophic levels, can have unintended effects throughout an ecosystem, and even thousands of miles away.

Question 15.20

Q: What can be done? Reducing and reversing the Gulf of Mexico’s dead zone (and other dead zones throughout the world) can be accomplished by (1) reducing fertilizer use, (2) preventing animal wastes from getting into waterways, and (3) controlling the release of other sources of nutrients (phosphorus as well as nitrogen) from industrial facilities into rivers and streams.

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