Scientists Say: Eutrophication

This process can occur when extra nutrients enter a body of water

Scientists Say: Eutrophication. When too much plant food goes bad.

This canal may look lovely, but all that green algae blooming on the surface is a sign of eutrophication, which could eventually suffocate any animals living below.

Sahehco/Wikimedia Commons (CC BY-SA 3.0)

Eutrophication  (noun, “Yu-TRO-fih-CAY-shun”)

This is a process in which a body of water receives a large bounty of nutrients, especially phosphates. These chemicals can enter the ecosystem naturally or through pollution such as fertilizer runoff. Algae and plants in the water respond to the extra phosphates by growing rapidly. But when the algae and plants die, bacteria break them down. As the bacteria go to work, they use up the oxygen in the water. Without dissolved oxygen in the water, many fish and other animals may suffocate.

In a sentence

When fertilizer runoff causes eutrophication, the lack of oxygen can kill other animals.

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Power Words

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algae     Single-celled organisms, once considered plants (they aren’t). As aquatic organisms, they grow in water. Like green plants, they depend on sunlight to make their food.

bacterium (plural bacteria)  A single-celled organism. These dwell nearly everywhere on Earth, from the bottom of the sea to inside animals.

decomposition  The process by which compounds in once-living things are broken down and returned to the environment; the process by which something decays or rots.

ecosystem  A group of interacting living organisms — including microorganisms, plants and animals — and their physical environment within a particular climate. Examples include tropical reefs, rainforests, alpine meadows and polar tundra.

eutrophication  The process by which a body of water becomes full of nutrients, which stimulate the growth of plants and algae. When these organisms die, bacteria decompose them and use up the water’s dissolved oxygen in the process. Without oxygen, animals cannot live in the water and the ecosystem may collapse.

oxygen  A gas that makes up about 21 percent of the atmosphere. All animals and many microorganisms need oxygen to fuel their metabolism.

phosphate  A chemical containing one atom of phosphorus and four atoms of oxygen. It is a component of bones, hard white tooth enamel, and some minerals such as apatite. It is a primary ingredient in most plant fertilizers.

nutrients  Vitamins, minerals, fats, carbohydrates and proteins needed by organisms to live, and which are extracted through the diet.

runoff    The water that runs off of land into rivers, lakes and the seas. As that water travels over land, it picks up bits of soil and chemicals that it will later deposit as pollutants in the water.

sediment  Material (such as stones and sand) deposited by water, wind or glaciers.

Bethany Brookshire was a longtime staff writer at Science News Explores and is the author of the book Pests: How Humans Create Animal Villains. She has a Ph.D. in physiology and pharmacology and likes to write about neuroscience, biology, climate and more. She thinks Porgs are an invasive species.

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