Dead Zones

We’ve seen a lot of issues with our food system and how it is negatively affecting people and our world. Let’s take a closer look at one of these issues that has to do with Iowa.

Back in the 1970's and 1980's, local fisherman started to notice areas of the Gulf of Mexico in which very few things lived.

QUESTION: How might you explain why things are dieing? What could you go and do to investigate these things? (Toxins were not killing the living things!)

Scientists determined it was because of low oxygen levels: VIDEO: 0:00 - 1:22 - Dead Zones 2 (file name in folder)

Brainstorm ideas with a partner: So, what can affect the level of oxygen in water? What increases oxygen levels? What decreases oxygen levels?

Things that do photosynthesis (discuss plants and algae)

Things that use oxygen - What do these organisms use the oxygen for? (discuss cellular respiration, and the fact that plants and algae also use oxygen)

The moving of water (Discuss surface area - fish tanks, surfaces of 3 different wetlands doc, surface area of a bubble or water droplet, 20% O2 in air vs. less than 1% in water - diffusion)

Temperature (molecules moving faster = harder to hold gasses in a liquid)

If these things aren’t coming up, show them the picture of different wetlands with different DO measurements (Word doc in folder)

DO article Read Aloud

Discuss the factors that affect DO

Discuss BOD

So what is BOD? Biochemical Oxygen Demand (BOD)

Which part of the model is demanding oxygen?

Organisms eating organic matter and using oxygen.

So where does the organic matter come from that these organisms are using?

Measure initial DO of projects

Develop a model for what affects DO

How can we fix this issue of low oxygen levels?: VIDEO: Ocean Frontiers (20 minutes) (non-point sources)

Measure final DO of projects

Analyze DO results vs. predictions

How do the results compare to predictions? Discussion of model creation based on tests and observations. How can we explain why we measured the values of DO that we did? How does our new understanding tweak our model?

DO higher in plants or algae?

DO lower in organic matter?

DO lower in fertilizer?

DO lower in dead organisms?

Relate DO to photosynthesis and cellular respiration - discuss the model

Relate increase or decrease in DO to populations of organisms and the abundance of their resources

Activity: What affects the oxygen level of water? How can we understand these things from a system perspective in order to help fix the problem?

How can we test each of these to see if they are adding or removing oxygen from water?

Play around a little bit with some water - test it with the oxygen probes

1st measure DO of tap water, then shake the water up and test the DO again.

Setup other longterm tests



Organic matter

living things from bottom of fish tank

Use the model to predict what would happen in a container with fertilizer

This model’s prediction does not fit our observation of reality.

So fertilizer does directly affect photosynthesis, but not cellular respiration. Which process must fertilizer indirectly affect if it is going to decrease the oxygen level?

Transition: So, photosynthesis and Cellular Respiration affect the oxygen level - How could Iowa affect either of these things?

Local connection - Iowa’s nutrient problem

VIDEO: Gulf Tides (6 minutes) (point vs. non-point)

VIDEO: Nitrogen Removal Basics (12 minutes) (point sources)(talks about water treatment plants and different forms of nitrogen)

Water Pollution Control Facility - Field Trip

What role does decomposition play in the “cleaning” of our waste water?

What is removed from the water and how?

What is Biochemical Oxygen Demand (BOD) and how does this relate to BOD?

To what extent would it feasible to treat storm water at a facility like the water pollution control plant?

What changes will the Ames plant have to make in the future in order to comply with the new recommendations by the EPA for nutrient reduction?

Transition: So why are humans now having this impact? Population

Assessment Question:

-Explain how the Dead Zone in the Gulf of Mexico occurs and why Iowa is linked to the problem. Be specific in how Iowa affects the Dead Zone.

-How might a hurricane in the Gulf of Mexico affect the Dead Zone, and WHY?

Objective: Explain ways in which humans can alter the equilibrium in ecosystems (e.g., human population growth, technology, and consumption; destruction of habitats, etc.).

Objective: Describe factors affecting population growth of all organisms, including humans. Relate these to factors affecting growth rates and carrying capacity of the environment.


Dead Zones