How Does Eutrophication Work? Causes, Process and Examples

Last Updated: Mar 24, 2019

Eutrophication Process

Eutrophication occurs in water bodies when too many nutrients are introduced. This is often near farm fields where farmers apply excess nutrients to the soil.

Because of runoff from farm fields, fertilizer enters the water. Eventually, it drains into the water body or leach into the ground.

In turn, the fertilizer rich in nitrate and phosphate sparks the overgrowth of plants and algae in water bodies.

This is how come eutrophication means “well-nourished” in Greek. But in this case, it’s more like an “over-nourished” water body.

Now that you have the basics of the eutrophication process, let’s detail the causes and examples of eutrophication in lakes.

READ MORE: 4 Steps of Nitrogen Cycle: The Key to the Food Chain

Over-fertilization starts the eutrophication process

Eutrophication Process

Basically, over-fertilization of water causes algae to grow on the surface. When fertilizer enters into the water, this becomes food for algae.

Because eutrophication stimulates algae growth, it’s common to see thick green blooms in the water. But the issue with algae is that it absorbs sunlight preventing sunlight from reaching the bottom.

When algae grows to such an extreme level, it entirely stops light reaching plants in the water. Eventually, plants that need sunlight cannot photosynthesize and die.

Especially, blue-green algae or “cyanobacteria” can be harmful to plants and humans. For example, it can be toxic if consumed. This type of algae is becoming a major environmental issue in most parts of the world.

Algal blooms and oxygen depletion are eutrophication effects

Eutrophication Effects

As algae begins to form, it blocks sunlight from entering the bottom of ponds, lakes and rivers. As more nutrients drain into the water, eutrophication repeats in a vicious “algal bloom cycle” and releases more nutrients in the water.

When algae receive enough sunlight, they produce oxygen through photosynthesis and release it in the water. But without light, algae stop generating oxygen and consume it instead.

When algae die, bacteria begin to decompose the remains, using up oxygen for respiration. Eventually, the decomposition causes the water to become depleted of oxygen. Over time, this causes the water to carry less oxygen than before.

It can reach a certain point when fish cannot swim and suffocate to death in the water. Overall, a eutrophic lake can no longer support life.

Finally, water without oxygen is anoxic and over time becomes a dead zone. When a water body reaches this point, it can no longer support fish and aquatic life like amphibians.

Dead zones are the worst case scenario from eutrophication

eutrophic dead zones hypoxia

Eutrophication disturbs the aquatic life through nitrogen-enriched fertilizer. Over time, this imbalance can cause aquatic life to start dying and in the worst case scenario a complete dead zone.

And dead zones are more concentrated where we have industrialized nations. Especially, industrial farming practices that contains nitrogen and phosphate or animal waste.

For example, here is the world of dead zones. You can see areas like the Caspian Sea completely filled with algal blooms.

In the northern Gulf of Mexico adjacent to the Mississippi River, this is the largest hypoxic zone in the United States (and the second largest worldwide).

How can we fix dead zones? It’s costly to reduce. The best answer is preventative techniques to reduce fertilizer or completely retiring cultivation near eutrophic risk zones.

Ecosystem threats in the world

Eutrophication can end in disaster for fisheries, tourism and local economies. We rely on clean, healthy water for aquatic life and animals that count on it in the food chain. Blue-green algae in itself is harmful to pets and for water consumption.

As we reshape the land, a clean water supply becomes a serious threat to people. Where do other threats exist for climate, ecosystems and the biosphere in general? Check out the articles below:

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    Whether it’s agriculture, industry, vehicles, electricity or natural disasters, methane, carbon dioxide and CFCs are the major air pollution sources that contribute to climate change.
  • Human Footprint: Effects of 7.6 Billion People on Earth
    In flesh and blood, 7.6 billion humans live on Earth. The emergence of humans has left a profound impact. The demand for resources is the human footprint.
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