This satellite image of summer conditions in the Gulf of Mexico south of Texas, Louisiana and Mississippi (US) is from the MODIS/Aqua satellite. Red and orange colors indicate the large amounts of phytoplankton that have multiplied because of nitrogen-rich water entering the Gulf at the Mississippi River Delta. When the phytoplankton die and decompose, oxygen is taken from the water and other marine life can not survive. This is known as a dead zone.

Fertilizing the Earth with Nitrogen

Plants need nitrogen to grow. Plants get the nitrogen they need from the soil. In an effort to grow more crops, people have been making nitrogen fertilizers and adding them to crops. This has been very successful. It has allowed people to farm on lands that had not been very fertile. However, fertilizers are often overused, and that can cause problems.

Nitrogen from fertilizers sinks into soils and then washes into waterways causing too many nutrients. In freshwater lakes, rivers, and streams the nitrogen causes aquatic weeds to grow, filling the entire lake, river, or stream. Algae cloud the water green and slimy algal scum coats shallow rocks.

When the nitrogen-rich water gets to the ocean, it causes algae to grow and reproduce very quickly. As the huge amounts of algae use up the nitrogen, die, and decompose, oxygen in the water is used up. Animals can not survive without oxygen. They flee to another part of the ocean if they can, or they die. This happens where the Mississippi River enters the sea at the Gulf of Mexico. It also happens in about 150 other places in the world’s oceans.

Last modified January 19, 2010 by Randy Russell.

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