Eutrophication &

Limiting Factors

What is Eutrophication?

What is Eutrophication?

• Eutrophication happens when added nutrients(usually N and P) make their way into a body of water, resulting in massive algae blooms and the depletion of oxygen

• Where is the phosphorus & nitrogen coming from?

– Sewage & detergents

– Manure and fertilizer runoff from lawns & farms

Characteristics of a Healthy Lake or Pond:

• Sunlight is able to reach deep into lake.

• Abundant plant and animal life.

• The Lake is deep

• Little or no algaepresent

Fertilizer Runoff – Part 1

• Fertilizer from a nearby farm field runs off into the lake (washed down slope by rainwater)

• The excess amount of nitrogen in the fertilizer causes Algal Blooms (overgrowth of algae) on the surface of the water.

• The sunlight can’t reach as deep as normal into the water and aquatic plants underneath the algae layer start to die.

• The algae bloom begins to use up a lot of the oxygen in the water, and animals begin to die.

Fertilizer Runoff – Part 2

• Dead organisms sink to the bottom of the lake.

• Decomposers (like bacteria) aid in the break down of the dead plants & animals.

• The more there is to decompose, the larger the decomposing bacteria population becomes.

• The bacteria use up even more oxygen, which continues to deplete the lake of O2

• Even more fish die, eventually leading to a “dead” lake

Eutrophication can result in a pond or lake filling in with dead and decomposing sediments over time

(not always, sometimes the lake can be rejuvenated)

We call this

aquatic succession

Example of Eutrophication in the U.S. / Michigan

Beaches were closed

What is a Limiting Factor?• Definition: an environmental factor that tends

to limit population size.

• There are specific things in specific amounts that every organism needs.

• Whichever resource is in the shortest supply determines how many organisms will survive, and that is the limiting factor for that population.

Limiting Factors, continued

• Example: My recipe for brownies requires

2 eggs, 3 Tbsp oil, ½ cup cocoa powder

• In my kitchen, I have:

6 eggs, 12 Tbsp oil, and 1 cup cocoa

How many batches of brownies can I make?

What’s the limiting factor?

Limiting Factors, continued

• Need 2 eggs per batch: 6 eggs will make 3 batches of brownies

• Need 3 Tbsp oil per batch: 12 Tbsp oil will make 4 batches of brownies

• Need ½ cup cocoa powder per batch: 1 cup cocoa powder will make 2 batches of brownies

• How many batches can I make? What’s the limiting factor?

• I can make 2 batches of brownies.

• Cocoa powder is the limiting factor.

Limiting Factors, continued

• If Nitrogen were the limiting factor in a plant population (preventing the population from growing past a certain size) and MORE NITROGEN WAS ADDED, what would happen?

• More Nitrogen = more plants

• It would be like buying more cocoa powder…I could make more brownies!

Example Questions:

• What is the limiting factor for a population of plants in a desert ecosystem?

• What is the limiting factor for a population of newly hatched sea turtles?

• What are two limiting factors for the population of infants and children in Kenya or Ethiopia?

Availability of water

Predators, like seagulls

1. Availability of food 2. Availability of medicine

More Example Questions:

• What are the two biggest limiting factors for the wolf population on Isle Royale?

• What is the limiting factor for the fish population in a lake that is undergoing eutrophication?

1. Moose/Prey 2. Healthy Mates

Amount of oxygen in the water