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Human Causes of Eutrophication

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  • 0:06 Bodies of Water
  • 0:58 Eutrophication
  • 2:37 Human Causes
  • 5:28 Lesson Summary
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Lesson Transcript
Instructor: Rebecca Gillaspy

Dr. Gillaspy has taught health science at University of Phoenix and Ashford University and has a degree from Palmer College of Chiropractic.

Eutrophication occurs when a body of water becomes overly enriched with nutrients. While this can happen naturally, accelerated eutrophication is typically the result of human activities. Learn about the human causes of eutrophication.

Bodies of Water

It was a pleasant afternoon in Timmy's neighborhood, so he decided to take a bike ride. As he traveled along the community bike path, he came across a pond and thought it would be a good place to stop and rest. Timmy noticed that the water in the pond was crystal clear, and there was very little algae and plant growth. 'What a beautiful lake,' Timmy thought to himself. After a few minutes, Timmy hopped back on his bicycle and headed down the path. Before long he came to another pond and decided to catch his breath again. When Timmy looked into the water at this pond, he noticed that it was cloudy and green due to so much algae and plant growth.

What Timmy was seeing in the second pond was a process called eutrophication. In this lesson, we will learn more about this process and how it can be caused by human activities.

Eutrophication

Eutrophication is the process by which a body of water becomes overly enriched by nutrients. You can recall this term by remembering that the word 'eutrophic' comes from the Greek language and means well-nourished. Therefore, a body of water that has undergone eutrophication is a 'well-nourished' lake.

While it might sound like a good thing to have extra nutrients added to water, eutrophication typically has a detrimental effect. An overabundance of nutrients stimulates the rapid growth of algae and aquatic plant life. This excessive growth depletes dissolved oxygen levels within the water to a point where other organisms, such as fish, cannot survive.

The problem is intensified when these large collections of algae die and begin to decay. The bacteria that decompose the dead algae require oxygen, which consumes even more dissolved oxygen in the water, essentially suffocating other organisms. Dissolved oxygen is the amount of oxygen contained in a body of water. It is an important indicator of the health of a water body and its ability to support a diverse balance of aquatic organisms.

When eutrophication occurs, a body of water can undergo explosive growth of algae at or near the surface of the water, referred to as algal blooms. When algal blooms are dense, they form visible green or yellowish-brown coverings that appear to float on the water surface. This blocks sunlight that is needed by organisms in the water and further depletes oxygen.

Human Causes of Eutrophication

Eutrophication can be a natural process that occurs over time due to natural runoff of soil nutrients and the decay of organic matter.

However, use of the term came into common usage when human causes of eutrophication were identified. Eutrophication is typically the result of human activities that contribute excess amounts of nitrogen and phosphorus into water.

Agricultural fertilizers are one of the main human causes of eutrophication. Fertilizers, used in farming to make soil more fertile, contain nitrogen and phosphorus. The use, or overuse, of fertilizers can cause these nutrients to runoff of the farmer's field and enter waterways. The same fertilizers that were intended to enhance crop growth now enhance the growth of algae and aquatic plants. Fertilizer runoff can occur from other sources, including lawns and golf courses, but agricultural practices are a main source of nutrient pollution.

Sewage contains both organic and inorganic nutrients that can find their way into bodies of water. Biochemical oxygen demand or B.O.D. is a concept that is important to sewage treatment. It is defined as a measure of the amount of oxygen required by aerobic microorganisms to decompose organic matter in water. Bacteria and other aerobic microorganisms use oxygen to metabolize organic matter, such as sewage. If sewage enters a body of water, microorganisms in the water begin to consume the organic matter and deplete dissolved oxygen.

Aquaculture, which is the growing or farming of fish, shellfish and aquatic plants, is a growing source of eutrophication. Aquatic organisms can be 'farmed' in water pens that are partitioned by nets. If not properly managed, uneaten particles of food along with excrement from the fish can add to increased levels of nitrogen and phosphorus in surrounding water.

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