Eutrophication
Dr. Tanya McKinney
DEEP WORKSHOP
Mississippi Standards addressed (5th-8th Grade)
 Inquiry Strand
 Life Science Strand, Competency #3, Objective E
PURPOSE:
 To introduce students to the concept of eutrophication.
 To investigate the process of eutrophication.
LERNING OBJECTIVES:
 Observe the effects of excess nitrogen phosphates on an aquatic ecosystem.
 Compare the growth of organisms in different levels of nutrients.
 Predict if the observed eutrophication in their local environment is due to excess nitrogen,
phosphorous, or both.
INTRODUCTION
An ecosystem is defined as a community of organisms living together and the biotic (living) and abiotic
(nonliving) factors that affect their growth and survival. In an aquatic ecosystem, the total number and variety
of living organisms present is dependent on the existing resources and the types of interactions occurring
between organisms. In this exercise, we will explore aquatic microbes and their impact on the ecosystem.
We will do by focusing on algae, nutrient availability, and the process of eutrophication.
Aquatic microbes include both prokaryotic (bacteria) and eukaryotic organisms. The eukaryotic
microbes are algae, protozoa, and fungi. Microbes are present in large quantities and play a major role in
determining the health of the aquatic environment.
Microbes, like all living organisms, require energy to grow, reproduce, and survive. Thus, they may be
classified according to how they obtain their energy. Remember that the sun is the ultimate source of energy.
Those organisms that can directly use the sun’s energy are classified as autotrophs or primary producers.
They manufacture their own organic material (food) via photosynthesis. Photosynthesis is a process that
utilizes carbon dioxide and water to produce glucose (a sugar) and oxygen. In the aquatic environment,
photosynthesis is carried out by plants, algae, and blue-green bacteria (also known as cyanobacteria). Algae
and the cyanobacteria are sometimes referred to as phytoplankton.
Autotrophs produce food or serve as a source of food for organisms known as heterotrophs or
consumers. These organisms obtain energy by consuming autotrophs or other heterotrophs. Heterotrophs
are typically classified according to what they eat:
 Herbivores eat only plants and are considered to be primary consumers. Manatees and some
protozoans are examples of herbivores.
 Carnivores eat animals and are called secondary consumers. The great white shark is an example of an
aquatic carnivore.
 Omnivores eat both autotrophs and heterotrophs. Bream are an example of omnivorous aquatic
organisms.
 Detritivores (decomposers) eat dead organic matter (detritus) such as dead organisms, feces, fallen
leaves, or wood. They include bacteria, fungi, worms, and insects.
Autotrophs and heterotrophs are linked by their feeding relationships. Energy is transferred from one
trophic (feeding) level to the next. The transfer of food energy from autotrophs to herbivores and carnivores
or omnivores is called a food chain. An example food chain is algae → protozoa → small insects → large
aquatic insects → small fish → large fish. Multiple food chains linked together form a food web. See
figure 1.
Figure 1. Aquatic Food Web
Detritivores also link autotrophs to heterotrophs. They play a major role in breaking down organic
matter and returning elements such as carbon and nitrogen to abiotic sources such as soil, water, and air.
Primary producers then utilize these elements to make organic compounds such as sugars.
The amount of energy present in an ecosystem controls the fate of the ecosystem. In aquatic
ecosystems, the amount of light and nutrient availability determines how much energy/food is produced by
primary producers. Interestingly, in aquatic ecosystems, nutrients levels may be more limiting than light. A
limiting nutrient is defined as an element that must be added for production to increase. Nitrogen and
phosphorous are the most important nutrients for growth of primary producers such as algae, cyanobacteria,
and aquatic plants. These nutrients are typically derived from the erosion of minerals and soils, organic
matter or from humans. However, large amount of a limiting nutrient may be harmful to the aquatic
ecosystem. Excessive amounts of nitrogen and/or phosphorous have been shown to cause eutrophication.
Eutrophication is the process in which a water body such as a lake becomes enriched with nutrients
such as phosphorous resulting in excess growth of primary producers. Natural eutrophication occurs over a
long period of times – thousands of years- and ends with a deep water body becoming shallow or nonexistent.
However, humans through various activities have sped up the process such that it occurs in decades.
Eutrophication due to the action of humans is commonly referred to as “cultural eutrophication”.
Excess nitrogen and phosphorous are added to water bodies by point (known) and nonpoint (unknown)
sources of pollution. Point sources include untreated or partially treated sewage, septic system output,
construction whereas nonpoint sources are fertilizer runoff from agriculture or lawns, grass clippings, and
erosion to name a few.
When present in excess, nitrogen and/or phosphorous cause a sharp increase in the growth of algae
resulting in an algal bloom. Algal blooms have detrimental impact on the aquatic ecosystem due to:
 Decreased light availability. Algae blooms form mats (green scum layer typically observed) due to their
rate of reproduction be faster than the rate of consumption. Lack of light decreases the production of
energy (food) and oxygen by plants and other aquatic autotrophs living in deeper waters.
 The water becomes depleted of oxygen due to lack of production by autotrophs in deeper waters and
due to detritivores utilizing oxygen when consuming dead and decomposing algae.
 Lower oxygen levels result in the death of fish and other organisms that need high levels of dissolved
oxygen such as trout, salmon, and bass. The water body becomes populated with organisms that can
survive low oxygen levels such as carp, catfish, and mosquito larvae.
 Over time, the depth of the water body will decrease.
 Some algal species produce toxins that can cause death or illness.
Thus, eutrophication disrupts food webs and results in alteration of the entire aquatic ecosystem.
ACTIVITY
MATERIALS
 Scenedesmus Culture from Carolina Biological ( You may also use Oscillatoria or Anabena. These are
filamentous cyanobacteria.
 Spring or Distilled Water
 Alga Gro Media Concentrate
 16oz jars or plastic clear soda bottles. If you use the soda bottles be sure to wash using water
containing chlorine bleach. Rinse well and let dry.
 Graduated cylinders
 Plastic wrap
 Stir rods
 Light (20W wide spectrum fluorescent grow lights or daylight spectrum incandescent bulbs or place
cultures in sunny window. Do not place in direct sunlight because this may cause the culture to
overheat.
 Microscope slides
 Cover slips
 Plastic droppers
 Miracle Gro Fertilizer
PROCEDURE:
1 Week prior to start of lab exercise prepare Alga Gro medium. The Alga Gro concentrate should be diluted
1:50 in spring water. (20ml in 1L, 10ml in 500ml, 2ml in 100ml). Inoculate with 5mls of the algal culture.
Incubate for 7 days in a sunny spot or under a 20W fluorescent bulb. Your alga culture prior to starting the
experiment should have heavy algae growth (be very green or have large sediment at bottom).
DAY 1: Eutrophication Lecture Powerpoint
Break students into groups.
Have students use the following methods to set up the experiment.
1. Label containers Control, 2 % fertilizer, 8 % fertilizer, and 16% fertilizer
2. Add 100 ml of Alga Gro medium to the 16oz container.
3. Add 2ml of algal culture to each container.
4. To the control no fertilizer is added.
5. To container 2 add 2 ml of fertilizer and mix well.
6. To container 3 add 8 ml of fertilizer and mix well.
7. To container 4 add 16 ml of fertilizer and mix well.
8. Place all containers under a light source or in a sunny location. Do not place in direct sunlight because this
may cause the culture to overheat.
9. Prepare a wet mount of the algal culture. Have students record the number of cells observed within the
field of view.
10. Allow phytoplankton to grow for 7 – 14 days. Observe for changes in turbidity, color, growth.
11. You may also determine dissolved oxygen content, nitrate, and/or phosphate levels.
12. Students may prepare a second wet mount.
Scenedesmus, genus of colonial green algae with 4, 8, or 16 cells arranged in a row. A common component of
freshwater plankton. Upon growth in test substance morphology may change. The cells may be unicellular
instead of colonial. They may be round or spindle shaped.
SAFETY PRECAUTIONS
Students should wear goggles, gloves, and protective clothing while handling chemicals such as fertilizer and
unknown pond organisms. Be sure to review the safety cautions on the container of household fertilizer.
Students should wash their hands carefully after handling the pond water samples. Clean the work area with
disinfectant after completing the investigation.
DISPOSAL
Please dispose of algal cultures responsibly. Do not pour cultures down the drain without treating them first.
Algal cultures may be treated by adding bleach to the culture to make a 1% solution. Allow the bleach algal
mixture to sit overnight. Pour down the drain with the water running. Alternately, cultures may be brought to
a boil in a microwave safe container in the microwave. An odor may occur. However, the microwave is not
contaminated.
TECHNIQUES TO DEMONSTRATE
Depending on your students’ level of experience with microscope techniques, you may wish to demonstrate
how to make a wet mount. Place a drop of pond water on a slide with a dropper. Pick up a coverslip and place
one edge on the slide. Slowly lower the other edge so that the water spreads out under it. Be careful not to
trap bubbles of air beneath the coverslip.
Eutrophication
Eutrophication is the process in which a water body such as a lake becomes enriched with nutrients
such as phosphorous resulting in excess growth of primary producers (algae, plants, cyanobacteria). Natural
eutrophication occurs over a long period of times – thousands of years- and ends with a deep water body
becoming shallow or nonexistent. However, humans through various activities have sped up the process such
that it occurs in decades. Eutrophication due to the action of humans is commonly referred to as “cultural
eutrophication”.
Excess nitrogen and phosphorous are added to water bodies by point (known) and nonpoint
(unknown) sources of pollution. Point sources include untreated or partially treated sewage, septic system
output, construction whereas nonpoint sources are fertilizer runoff from agriculture or lawns, grass clippings,
and erosion to name a few.
When present in excess, nitrogen and/or phosphorous cause a sharp increase in the growth of algae
resulting in an algal bloom. Algal blooms have detrimental impact on the aquatic ecosystem due to:
 Decreased light availability. Algae blooms form mats (green scum layer typically observed) due to their
rate of reproduction being faster than the rate of consumption. Lack of light decreases the production
of energy (food) and oxygen by plants and other aquatic autotrophs living in deeper waters.
 The water becomes depleted of oxygen due to lack of production by autotrophs in deeper waters and
due to detritivores utilizing oxygen when consuming dead and decomposing algae.
 Lower oxygen levels result in the death of fish and other organisms that need high levels of dissolved
oxygen such as trout, salmon, and bass. The water body becomes populated with organisms that can
survive low oxygen levels such as carp, catfish, and mosquito larvae.
 Over time, the depth of the water body will decrease.
Thus, eutrophication disrupts food webs and results in alteration of the entire aquatic ecosystem. In this lab,
you will observe artificial eutrophication in an aquatic ecosystem.
OBJECTIVES
 Observe the effects of excess nitrogen phosphates on an aquatic ecosystem.
 Compare the growth of organisms in different levels of nutrients.
 Predict if the observed eutrophication in their local environment is due to excess nitrogen,
phosphorous, or both.
MATERIALS
 Scenedesmus Culture
 Alga Gro Media
 16oz jars or plastic clear soda bottles. If you use the soda bottles be sure to wash using water
containing chlorine bleach. Rinse well and let dry.
 Graduated cylinders
 Plastic wrap
 Stir rods
 Light source
 Microscope slides
 Cover slips
 Plastic droppers
 Miracle Gro Fertilizer
Procedure
1. Working with your group label containers Control, 2 % fertilizer, 8 % fertilizer, and 16% fertilizer.
2. Add 100 ml of Alga Gro medium to the 16oz container.
3. Add 2ml of algal culture to each container.
4. To the control no fertilizer is added.
5. To container 2 add 2 ml of fertilizer and mix well.
6. To container 3 add 8 ml of fertilizer and mix well.
7. To container 4 add 16 ml of fertilizer and mix well.
8. Cover each jar loosely with plastic wrap
9. Place all containers under a light source or in a sunny location. Do not place in direct sunlight because this
may cause the culture to overheat.
10. Prepare a wet mount of the algal culture. Record the number of organisms you observe in a single field of
view. If alga density is high, record the number as TNTC (too numerous to count).
11. Allow phytoplankton to grow for 7 – 14 days. Observe and record changes in turbidity, color, growth.
12. You may also determine dissolved oxygen content, nitrate, and/or phosphate levels. Your teacher will
decide if these assays will be done.
13. Prepare a wet mount of the algal culture. Record the number of organisms you observe in a single field of
view. If alga density is high, record the number as TNTC (too numerous to count).
1. Based on what you have learned concerning eutrophication, propose a hypothesis about the algal growth
in each of the test jars/bottles.
2. Observe the jars when you first set them up and at least once every three days for the next 1-2 weeks.
Make a data table to record the date, color, turbidity, and any other observations you make for each jar.
3. Complete the chart below using the data obtained from the wet mount.
Cell Number
Sketch some of your cells.
Analysis
After one week, which jar shows the most abundant growth of algae? What may have caused this growth?
After 2 weeks, which jar shows the most abundant growth of algae?
Which jars/bottle shows the least amount of growth at 1week? Which jars shows the least amount of growth
at 2 weeks?
Conclusions
Was your hypothesis supported or rejected? Explain using your data?
Did you obtain any unexpected results? If so, why do you think they occurred and how could they be
prevented?
How can eutrophication be prevented?