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What Are Algae Blooms? - Definition & Examples

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Instructor: Elizabeth Friedl

Elizabeth, a Licensed Massage Therapist, has a Master's in Zoology from North Carolina State, one in GIS from Florida State University, and a Bachelor's in Biology from Eastern Michigan University. She has taught college level Physical Science and Biology.

An expeditious increase in the density of the algae resulting from sunlight and nutrient pollution creates an algae bloom. Learn its definition and effects as well as the different examples of types of algae blooms. Updated: 09/13/2021

What Are Algae Blooms?

Aquatic ecosystems are dynamic habitats, but ones that require that a delicate balance of nutrients be maintained. Aquatic ecosystems with too few nutrients in the water are referred to as ogliotrophic. Those with too many nutrients are eutrophic.

Eutrophication is a problem that is usually caused by human activity. It is the result of excess nutrients finding their way into the water from the fertilizer used on farms, lawns, and golf courses, as well as wastewater and storm water runoff. When this runoff is combined with abundant sunlight and warm temperatures, algae blooms may occur.

Algae are photosynthetic microorganisms that are found in most aquatic habitats. Algae love runoff nutrients, and an algae bloom occurs when nutrient pollution and lots of sunlight create a rapid increase in the density of the algae.

When an algae bloom does happen, the stream, river, lake, or ocean becomes covered with algae, creating a thick mat of surface scum. Bright green colored blooms develop from cyanobacteria, which are also known as blue-green algae. Not only does this not look very nice, but it blocks sunlight from reaching the water underneath the surface, which can have far reaching consequences for the organisms living there.

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  • 0:00 What Are Algae Blooms?
  • 1:20 The Effect of Algae Blooms
  • 2:05 Types of Algae Blooms
  • 3:17 Prevention
  • 3:39 Lesson Summary
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The Effect of Algae Bloom

While algae is a natural and important part of aquatic ecosystems, too much of it can have harmful effects. Many aquatic organisms need oxygen to breathe, and this comes from dissolved oxygen in the water. When sunlight doesn't reach the water, photosynthesis, an oxygen-producing process, decreases, and the animals that depend on dissolved oxygen literally suffocate in the water.

The amount of oxygen is further decreased when these animals die. Dead animals sink to the bottom and are broken down by microbes. These microbes use oxygen to do their work, which makes for even less available dissolved oxygen. If the amount of dissolved oxygen becomes low enough the water becomes hypoxic, and a dead zone occurs.

Types of Algae Blooms

There are many types of algae, which means there are just as many types of algae blooms. Freshwater algae blooms occur in freshwater rivers, lakes, and streams. The algae in these systems are not usually harmful to people, but can still cause large fish kills and other negative effects. Some types of algae produce toxins, and if they become too abundant they can affect not only the aquatic organisms in the water, but also people and terrestrial animals that come in contact with the water. These are called harmful algae blooms. People who swim in eutrophic waters may develop skin, eye, and respiratory issues because of a harmful algae bloom.

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