Phosphorous and Nitrogen Agriculture Communicating science


An elaboration of eutrophication

You might be more familiar with the symptoms of eutrophication than the term itself

As a limnologist, I am interested in eutrophication. But why? To answer that question, we should first start with the question, "what is eutrophication?" 

The word “eutrophication” derives from the Greek eutrophia , from eu, which means "well" plus trephein, which means "nourish". I doubt that clarified things.

In 1993, Dr. Scott Nixon proposed a definition of eutrophication as ‘‘an increase in the rate of supply of organic matter to an ecosystem”. This was an important step, because for decades, scientists and natural resource managers had been struggling with vague or inconsistent definitions. Eutrophication can apply to ecosystems on land, like a grassland, but here I will focus on water bodies. 

Now this probably still hasn't answered the question "what is eutrophication?", but keep reading...

In water bodies, the term “organic matter” refers to carbon-based compounds in living or previously living organisms and their waste products. Organic matter can be produced internally or imported from external sources. An internal source is carbon-fixation (photosynthesis) by aquatic plants and algae. External sources include a tree or leaves falling into a lake or river.

Many areas are naturally eutrophic, so it isn't necessarily a bad or undesirable condition. Also, lakes can become eutrophication over time, as they age, but it is a generally slow process that occurs over long time periods. 

Today, humans have dramatically increased the pace of eutrophication and where it occurs by discharging sewage and industrial wastewater into water bodies and through intensive, “industrialized” crop, meat, milk, and egg production. Globally, human-caused eutrophication is a major stressor for lakes, rivers and coastal areas.

Nitrogen and phosphorus are critical for all life and are important crop fertilizers. In water bodies, these nutrients increase the growth rate and abundance of algae (aka organic matter). This could mean more food for fish and more fish, which could make a lake or river more attractive for recreational activities, like fishing. But there can also be too much of a good thing. 

Increased abundance of algae can reduce water clarity and, in extreme cases, make water look like green slime. Algal blooms cause unpleasant odors when they decompose. Together, odors and green slime could ruin a day at the beach.

Also, some algae produce toxins that contaminate drinking and bathing water as well as fish and shellfish.

Algal bloom Lake ErieHere is an algal bloom seen on the shore of Lake Erie (photo from NOAA). Algal blooms like this can sicken or kill animals and people that drink the water. Even contact with the water can cause rashes and lesions.  

Eutrophication has other symptoms that aren’t as visible as algal blooms

As algal blooms fade and die, they are decomposed by microorganisms and small aquatic animals. This process consumes oxygen in the water column faster than it can be replaced by photosynthesis and diffusion from the overlying water, resulting in areas that don't have enough oxygen to support life. These are also called dead zones, which I discussed earlier

Eutrophication also changes the composition of fish, zooplankton (small animals that are an important part of the food web), and algae and aquatic plant communities.

The dead zones and changes in biodiversity likely wouldn't affect your ability to use a lake for boating or swimming. They could affect recreational and commercial fishing, but many lakes are stocked with sport fish, so the impact of eutrophication might not be apparent.

Why do I care about eutrophication?

I study eutrophication because I am fascinated by how nitrogen and phosphorus move through ecosystems and the effect that changing the amount of nitrogen and phosphorus inputs has on ecosystems. Nerdy, yes. But, I also study eutrophication because I am concerned about the health of our shared water resources. Water is essential for life, but it is also essential for our overall wellbeing. Being able to go swimming, boating, or fishing, or even just looking at a lake, river, or coastline is something that everyone should be able to enjoy. 


You can read more about eutrophication herehere, and here.

Michelle McCrackin

Michelle McCrackin