Sex Changes, Drugs, and Rockin’ Dead Zones
A trifecta of lessons
Overview
This lesson consists of 3 activities, all interrelated yet can be split into individual lessons as well. The
overall theme of the lessons are to investigate the effect human introduced contaminants into aquatic
systems have on individual organisms, populations, communities, and ecosystems. We will investigate
how farming in the “Bread Basket” of America can contribute to a growing “Dead Zone” in the Gulf of
Mexico and then create our own dead zones in lab. Students can then become a participant in the
formation of dead zones in an interactive simulation/game. The final component of the lesson focuses on
investigating the effect a novel (or never before seen) contaminant has on vulnerable frog populations.
Objectives
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Be able to describe how a dead zone occurs – from the human sources of pollution to
how it sparks blooms of life resulting in death
Simulate the formation of a thriving ecosystem and dead zone
Be able to describe how human sources of pollution can impact population dynamics
Understand the flow of energy through aquatic ecosystems
Length of Lesson
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3 Lessons of 50 minutes and 10 minutes for sampling every other day for 3 weeks:
o 1 lesson for the introduction of dead zones, the lab and simulating dead zone
formation
o 1 lesson to wrap-up the dead zone lab (sampling, graphing, assigning
homework)
o Novel contaminants and frog sex ratio (lecture intro, activity)
Grade Levels
8th – 12th grade
Notes for grade-level appropriate content or extension are noted throughout lesson plan.
Standards (Provided are examples and not an exhaustive list of applicable standards)
Standard B1: Inquiry, Reflection, and Social Implications
B1.1 Scientific Inquiry
B1.2 Scientific Reflection and Social Implications
Standard B2: Organization and Development of Living Systems
B2.1 Transformation of Matter and Energy in Cells
B2.3 Maintaining Environmental Stability
B2.4 Cell Specialization
B2.5 Living Organism Composition
Standard B3: Interdependence of Living Systems and the Environment
B3.1 Photosynthesis and Respiration
B3.2 Ecosystems
B3.3 Element Recombination
B3.4 Changes in Ecosystems
B3.5 Populations
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Materials
Dead Zone Lab Activity
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X number of 500mL beakers, mason jars OR 1L bottles (with neck cut off)
o Number depends on the number of places sampled
Vernier Dissolved Oxygen (DO) Probe
Household fertilizer (N:P:K ratio of 3:10:3 - - avoid urea based fertilizers)
Natural aquatic systems to sample (lakes, streams, ponds, etc)
Plastic Wrap
Access to a high light area and dark area (cabinet or drawer) with same temperatures
Dead Zone Simulation
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A chalkboard or whiteboard to write out equations for photosynthesis and respiration and
to keep a running tally of before and after numbers of each system component. Other
information (diagrams, etc.) may be needed for clarity
Name Cards for each student – Either phytoplankton/nutrients or carbon dioxide/oxygen
cards
Long rope that can stretch across classroom
Frog Contaminants Lesson
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Scenario instructions/data handout
Decks of cards for 40% female and 90% female populations
o 10 sets of pre-sorted decks available from GK-12 program
Background
Humans have a large impact on their environment. Burning fossil fuel sources has led to
an increase in atmospheric CO2 levels resulting in rising temperatures, rising sea levels and other
climatic changes. Here we investigate a few examples of how humans directly impact their
surroundings as we increase the use of fertilizers and herbicides.
Aquatic organisms require oxygen, just as we do, to perform basic functions of life. The
more organisms that are present in an area, the more oxygen is consumed, this is termed the
biological oxygen demand (BOD). With the increase in fertilizer usage to increase crop yields, like
corn and soy beans, more and more fertilizer is washing off the farms and entering local drainage
ditches. Ultimately, these nutrients are being discharged out of the Mississippi River into the Gulf
of Mexico at the Mississippi River Delta. This nutrient rich water sparks algal growth (or algal
blooms) resulting in large amounts of algae that ultimately die and sink to the bottom of the
ocean. These dead algae settle to the bottom and are decomposed by microbes that require
large amounts of oxygen in the process. These microbes take up most of the oxygen out of the
water, creating an area with low oxygen concentrations, or a “hypoxic” area. Anything that
requires oxygen and is trapped in these hypoxic areas essentially suffocate, leading to a “dead
zone” or an area devoid of life. In this lab we will investigate these sequence of events and create
our own dead zones.
Amphibian populations are in decline worldwide. Many species are very susceptible to
changes in aquatic environments, including novel human contaminants. While people may be
familiar with some changes these contaminants may have on the individual level, such as causing
frogs to grow additional legs, individual-level changes may also have effects on population
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dynamics. This activity explores how two types of novel contaminants affect frog populations.
Endocrine disruptors are any chemicals that alter an animal’s hormone system. One result of
these endocrine disruptors entering aquatic systems is a change in the sex ratio in the population,
resulting in a greater proportion of females. Herbicides are another major class of contaminant.
While many herbicides will not immediately kill frogs that are exposed to them, they can have
other effects on population dynamics, such as reducing population growth rates or affecting the
immune system, making them more susceptible to disease which can lead to higher population
mortality. Adult size strongly influences reproductive success in many species of frogs.
Activities
Dead Zone Lab Activity
1. Follow instructions established on the “Dead Zone Student Worksheet” (can be found as an
additional resource).
2. Key notes before starting: This lesson will require sampling of an aquatic system, and should be
done when the weather is favorable to productivity (aka in the late Spring- early Fall). Also, once
the experiment has started, sampling will have to take place daily for 2-3 weeks. Sampling will
take a maximum of 10 minutes per class.
3. Also included in the “Dead Zone Student Worksheet” is a graphing activity (using the data they
collected) and follow-up questions that can be used as a group assignment or homework.
Dead Zone Simulation
0. Before the Lesson
a. Set up a large playing area that students can move around in – designate one end of
the room the air-water interface and the other end the sediment-water interface. One
side will be the Mississippi River discharge where nutrients come out.
b. Calculate the numbers of each of the four players to be assigned based on the
number of students in the classroom and the desired ratios (see dead zone game
instructions)
1. Introduce key terms
a. Hypoxia – low dissolved oxygen content
b. Eutrophication – enrichment of nutrients nitrogen and phosphorus needed for plant
growth
c. Stratification – the layering of water bodies due to different physical properties that
impede their mixing
d. Pycnocline – the surface across which water densities change abruptly
2. Write the equations for photosynthesis and respiration on the blackboard. It is a good idea to
keep these up during the game so that students can refer back to them. It is also important to
describe where these take place (photosynthesis occurs near the air-water interface while
respiration occurs in all organisms). For the purpose of the game we are simulating the
respiration from bacteria that decompose organic matter- this occurs near the bottom (watersediment interface).
3. Get two volunteers to help simulate the processes before the class plays. (See dead zone
game instructions.) It is useful to walk the class through the process of photosynthesis and
reproduction as a phytoplankton, and then decomposition involving respiration.
4. Pass out name cards for each student to wear in proportion to the number of students in your
class (see dead zone game instructions). It is useful to keep a running tally of the numbers of
each player at the beginning and end of each round on a chalkboard or whiteboard visible to
the class. Play the first round together, making sure each student understands their roles
before moving on, and clarifying any confusion. Once the simulation is over, write down the
numbers of each player.
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5. Set up a long rope across the playing area to serve as the pycnocline. Instruct students that
only phytoplankton are large enough to move across this playing area. See instructions for
round 2.
6. Continue with round 3, writing down before and after starting numbers of each player type
and discussing as a class what changes have occurred and why. It may be useful to pause
the game during round 3 when the number of phytoplankton have peaked to have students
look around and describe what is going on (algae bloom). At the end of the round discuss
what happened.
7. Additional simulations involving other organisms can also be performed or discussed(see
instructions).
Extensions and Modifications
1. Have students predict how many nutrients can be added to a system before hypoxia occurs. The
class can go through simulations to test these predictions (see more info in Kastler 2009)
2. Have students discuss how humans can prevent dead zones from occurring. Possibilities:
a. Town hall meeting where the class forms different sides who argue for competing
interests
b. Write a letter to the editor of a local newspaper to discuss the problems associated with
nutrient runoff
Frog-Contaminants Activity
1. If you will not be using pre-sorted decks from GK-12, assemble a 40% female deck and 90%
female deck for each group of students in the class. Each deck contains 40 cards. The 40%
female deck should contain 16 red suit cards and 24 black suit cards, while the 90% female deck
should contain 36 red suit cards and 4 black suit cards. Red and black cards should be evenly
split among the suits (unless that is something being modeled in an extension). If possible, 10
cards in each deck (4 red and 6 black for 40% female, 9 red and 1 black for 90% female) should
have a different color back, to indicate these cards as the starting population deck.
2. Follow instructions on handout to have students model populations with different sex ratios (40%
female or 90% female) that have either been exposed to an herbicide or have not been exposed.
3. Have students collect data from each scenario and graph the results.
4. Discuss the answers to follow-up questions.
Extensions and Modifications for Frog-Contaminants Activity
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Chytrid fungus could affect populations in all scenarios – in this case, roll a die to
determine whether the individual gets the disease (a 1 is chytrid in an individual not
exposed to herbicide, 1-3 is chytrid in individuals that have been exposed)
Pre-sorted decks contain equal numbers of hearts/spades and diamonds/clubs (not
exposed vs. exposed). Students could adjust decks to determine how increasing the
proportion of exposed individuals alters population dynamics.
Students could also experiment with additional sex ratios to see how that would affect
population dynamics.
Additional Resources
Kastler 2009 (see pdf)
Lake Erie as a case study:
http://www.epa.gov/lakeerie/eriedeadzone.html
Other activities you can do in your classroom -see Activity (Explore) – Density- for an activity that
investigates water stratification:
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http://www.teachoceanscience.net/teaching_resources/education_modules/dead_zones/access_cl
assroom_resources/
Another water stratification lesson:
http://oceanservice.noaa.gov/education/lessons/hot_cold_lesson.html
In this activity, you will explore the effects that different novel contaminants can have on frog
populations.
Baseline Instructions: For each scenario, you will need the appropriate population deck (10
cards) and draw deck (30 cards) provided. The 10 cards that start in the population deck
represent the initial population of ten individuals. The draw deck contains the offspring that will
be added to the population in each generation. First, shuffle the draw deck and set it aside face
down. Then shuffle the starting deck and place it face down.
1. Draw cards from the starting population deck two at a time. If a pair contains one black card
(male) and one red card (female), this indicates frogs that have successfully found a mate.
2. For each successful pair, add cards from the draw deck to the population (representing this
pair’s offspring). The exact number of offspring added per pair will depend on the conditions of
each scenario. Record the total number of cards as the number of frogs in the population for
Generation Two in the data table.
3. Reshuffle the population deck and repeat steps 1-2 to get population totals for Generations
Three and Four. Depending on the scenario, there may also be additional environmental
challenges that affect population size.
4. When you have collected data for each scenario, plot the data and discuss the trends you see.
Scenario #1: 40% Female, No Herbicide
Background: This scenario represents what might be considered a baseline, undisturbed
situation. A population where 40% of the individuals are female is considered typical for many
species. In this case, the population has not been exposed to herbicide pollution.
Modifications: Use the 40% Female deck. Red cards represent females, black cards represent
males. Each successful pair will add two offspring to the population.
Scenario #2: 90% Female, No Herbicide
Background: In this scenario, we include contaminants such as endocrine disruptors –
chemicals that can affect the system of hormones in the body. Tadpoles that are exposed to some
types of endocrine disruptors may change their sex, resulting in populations that have
significantly more females than is typical. In this case, you will investigate an initial population
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that has been exposed to these chemicals, resulting in a population that is 90% female. There has
not been any exposure to herbicides.
Modifications: Use the 90% Female deck. Red cards represent females, black cards represent
males. Each successful pair will add two offspring to the population.
Scenario #3: 40% Female, Exposed to Herbicide
Background: In this scenario, there has been no exposure to endocrine disruptors, so the sex
ratio of the population is at a typical level. Instead, we consider what happens when some frogs
are exposed to herbicide pollution. While many herbicides will not immediately kill frogs that
are exposed to them, they can have other effects on population dynamics, such as reducing
growth or affecting the immune system, making them more susceptible to disease. Adult size
strongly influences reproductive success in many species of frogs.
Modifications: Use the 40% Female deck. Red cards represent females, black cards represent
males. In addition, the suit of the card will indicate whether that frog has been exposed to
herbicide. Spades and hearts indicate that the frog has not been exposed, while clubs and
diamonds have been exposed.
Exposure to herbicide will influence how many offspring a frog can have. If neither parent has
been exposed (spade and heart), the pair will still add two offspring to the population. If one
parent was exposed while the other was not (spade and diamond or club and heart), the pair
will add one offspring to the population. If both parents were exposed (club and diamond), the
pair will add no offspring to the population.
In addition, scientists have found that frogs that have been exposed to some types of herbicide
have much greater mortality when they are later exposed to chytrid fungus. Chytrid fungus has
become a significant problem for amphibians in many parts of the world. In this scenario, after
reproduction for Generation Four has occurred, the population will be exposed to chytrid fungus.
You will eliminate all clubs or diamonds from the population before recording the total in the
data table for Generation Four.
Scenario #4: 90% Female, Exposed to Herbicide
Background: In this scenario, the population has been exposed to both disruptors and herbicide.
This will allow you to see how both contaminants together might alter population dynamics.
Modifications: Use the 90% Female deck. Red cards represent females, black cards represent
males. In addition, the suit of the card will indicate whether that frog has been exposed to
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herbicide. Spades and hearts indicate that the frog has not been exposed, while clubs and
diamonds have been exposed.
Exposure to herbicide will influence how many offspring a frog can have. If neither parent has
been exposed (spade and heart), the pair will still add two offspring to the population. If one
parent was exposed while the other was not (spade and diamond or club and heart), the pair
will add one offspring to the population. If both parents were exposed (club and diamond), the
pair will add no offspring to the population.
In this scenario, after reproduction for Generation Four has occurred, the population will be
exposed to chytrid fungus. You will eliminate all clubs or diamonds from the population before
recording the total in the data table for Generation Four.
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THE DEAD ZONE: Student Worksheet
Originally From and Special Thanks To: Teach Ocean Science.org
(http://www.teachoceanscience.net/teaching_resources/education_modules/dead_zones/access_cl
assroom_resources/)
MATERIALS
Clear 3 1L container, 500mL beakers, Mason Jars
Vernier lab probe (to measure oxygen)
Pond or stream water (Have fun sampling!)
Tap water
Fertilizer (Over the counter NPK 3:10:3, avoid urea)
PROCEDURE
1. If using 1L containers, cut the top off each container where the container tapers and
remove plastic/paper covering.
2. Fill one container with tap water and let sit overnight. Label the container “control.”
3. Fill the other two containers with pond, lake, etc. water.
4. Add 100 mg of each fertilizer to one of the remaining containers and mix thoroughly to
dissolve. Label this container “dead zone.” Label the remaining container “no nutrient.”
Place each container in a sunlit window for 5-7 days.
5. Use the oxygen probe to record the initial oxygen concentration in each container. Record
this info, as well as sight/smell descriptions in the data table on page 2.
6. Continue to record daily observations of the containers.
7. Plot the dissolved oxygen reading each day using the graph on page 3.
8. After 5-7 days (when an algal bloom has grown in the container), remove the dead zone
container from the sunlight and cover with plastic wrap (if a 1-liter container) or the
mason jar cap. Secure the plastic wrap with a rubber band and leave them in a dark
place.
9. Continue to record data each day for 7-10 days.
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DATA SHEET
Data table for observations and dissolved oxygen measurements
Day
Dead Zone Observations
Qualitative (visual)
Control Observations
Dissolved
Oxygen (DO)
mg/l
Qualitative (visual)
Dissolved
Oxygen (DO)
mg/l
1
2
3
4
5
6
7
8
9
10
11
12
13
14
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Graph your oxygen data for both the dead zone container and control container. Be sure to label
each line in your graph either “dead zone” or “control” and indicate on the graph which day you
put your containers in the dark.
Oxygen Change
Oxygen concentration (mg/l)
12
10
8
6
4
2
0
1
2
3
4
5
6
8
7
9
10
11
12
13
Day
BEST Experiment
Bioenergy Introduction
Updated February 14, 2011
pg.10
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QUESTIONS
1. What trend did you observe in oxygen readings for each container throughout its time in
the sunlight (increase/decrease/stay the same)?
2. Why did the oxygen increase/decrease/stay the same in each container?
3. Explain the different colors and oxygen levels in each container after a week of growth?
4. What happened to oxygen concentrations when you placed your containers in the dark?
Why?
5. How do you think a fish would react if you placed it in the dead zone container? Why?
6. What might be some effects on the marine food web when a large dead zone is present?
BEST Experiment
Bioenergy Introduction
Updated February 14, 2011
pg.11
9. Draw a picture or diagram of the processes that occurred in your dead zone container.
Include the following: nutrients, algae, photosynthesis, bacteria, respiration, and oxygen
depletion.
10. A farmer decides to use fertilizer on his corn this year. In the spring, he notices the pond
next to his corn field looks very green. In the past he has caught many fish in the pond,
but this year catches nothing. What do you think happened?
BEST Experiment
Bioenergy Introduction
Updated February 14, 2011
pg.12
Cheat Sheet for Herbicide Exposure Scenarios
Suit
Identity of Frog
Female
No exposure to herbicide
Female
Exposed to herbicide
Male
No exposure to herbicide
Male
Exposed to herbicide
Male is…
Reproduction:
Female is…
2
1
offspring offspring
1
0
offspring offspring
BEST Experiment
Bioenergy Introduction
Updated February 14, 2011
pg.13
40% Female
No herbicide
90% Female
No herbicide
40% Female
Herbicide
90% Female
Herbicide
Generation 1
Population
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BEST Experiment
Bioenergy Introduction
Generation 2
Population
Generation 3
Population
Generation 4
Population
10
10
10
Updated February 14, 2011
pg.14
What population trends do you see? What differences do you see between scenarios?
Does herbicide appear to affect population dynamics before introduction of chytrid?
Do there seem to be differences between scenarios in the proportion of frogs reproducing? What
consequences could this have?
BEST Experiment
Bioenergy Introduction
Updated February 14, 2011
pg.15
KEY
What population trends do you see? What differences do you see between scenarios?
40% female populations increase much more rapidly than 90% female populations
(depending on which cards are drawn, there may not be much growth at all in 90% female
populations). When herbicide exposure is introduced, those populations grow more slowly
than non-herbicide populations.
Does herbicide appear to affect population dynamics before introduction of chytrid?
Yes, herbicide has some non-lethal effects on frogs, since frogs that have previously been
exposed have fewer offspring. Students may see that their herbicide-exposed populations
are not growing as rapidly as populations with the same sex ratio that have not been
exposed.
Do there seem to be differences between scenarios in the proportion of frogs reproducing? What
consequences could this have?
90% female populations have very few frogs reproducing – there may only be one “male”
reproducing the entire time. In a similar situation in nature, this will lead to less genetic
variation. This could make the population more susceptible to certain diseases or may
make it less likely to adapt to new environmental challenges.
BEST Experiment
Bioenergy Introduction
Updated February 14, 2011
pg.16