Simulating and Solving Ocean Acidification (James Rice)

Side by side comparisons of a coral reef proceeding from healthy to dead in less than a year due to ocean acidification

Author(s)

James Rice, Northridge Academy High School

NGSS Engineering Standards

HS-ETS1-1. Analyze a major global challenge to specify qualitative and quantitative criteria and constraints for solutions that account for societal needs and wants.

HS-ETS1-2. Design a solution to a complex real-world problem by breaking it down into smaller, more manageable problems that can be solved through engineering.

HS-ETS1-3. Evaluate a solution to a complex real-world problem based on prioritized criteria and trade-offs that account for a range of constraints, including cost, safety, reliability, and aesthetics as well as possible social, cultural, and environmental impacts.Include the NGSS engineering standards which are addressed.

HS-PS1-6: Refine the design of a chemical system by specifying a change in conditions that would produce increased amounts of products at equilibrium.

NGSS Engineering Standards

PROBLEM - From the World Meteorological Organization

In this project, students will be researching:

chemical, biological, ecological, and economic effects of ocean acidification along North American shores and globally
mechanisms by which ocean acidification occurs
ways to simulate, measure, and modify this effect in the laboratory
the feasibility of scaling up any potential control method for use in restoring local, regional, and global ocean acidity

OPTIMIZATION - Specify the process of optimization

"Since the beginning of the industrial era, human activity has added 4 kg of carbon dioxide per day per person on average to the ocean. This anthropogenic CO₂ reacts with water to form an acid. As atmospheric CO₂ continues to increase, more and more CO₂ enters the ocean, which reduces pH (pH is a measure of acidity, the lower the pH, the more acidic the liquid) in a process referred to as ocean acidification. Along with the increase in acidity (higher concentrations of hydrogen ions, H+), there is also a simultaneous decrease in concentrations of carbonate ion (CO₃^2-). Reductions in CO₃^2- reduce the chemical capacity of the ocean to take up further CO₂ while also degrading the ability of many marine organisms to produce and maintain shell and skeletal material."

DESIGN -

Identify the primary driver of ocean acidification: anthropogenic CO₂
In groups, students will utilize the provided materials to:

Develop and/or implement a method for measuring acidity over the relevant pH range of seawater. The method needs to be precise enough for students to recognize pH changes on the order of what has been observed in the process of anthropogenic ocean acidification (+ or - 0.05 pH units)
Develop an aqueous buffer solution that simulates the pH behavior of seawater from among a variety of classroom materials. The simulated seawater will need to have "pre-industrial" and "acidified" pH levels that match with corresponding anthropogenic atmospheric CO₂ levels.
Develop and implement a method for generating/releasing anthropogenic CO₂ in the laboratory within time and budget constraints. Students will need to generate the CO₂ from materials costing less than $5 per group and demonstrate that CO₂ is indeed being generated.
Develop and implement a means for dissolving CO₂ in the simulated seawater within a single 50-minute class period.
Research a means for controlling the effects of the dissolved CO₂ on the simulated seawater and present the pros and cons for such a solution at the local, regional, and global level. Students will need to demonstrate the effectiveness of the method at the laboratory level.

OPTIMIZATION -

Depending on how much of the full project a teacher wishes to implement, as well as time and resources, students can work on optimizing the effectiveness of any one or all of the hands-on phases of the project based on data analysis collected from individual teams, the whole class, and potentially multiple class periods via CSCS.

Materials needed

Crash Course Chemistry videos on acid-base reactions, equilibrium, equilibrium equations, pH and pOH, and buffers:

Besides these informational resources, each student group should have:

A centigram scale
Two 250 mL Erlenmeyer flasks with corresponding 1- or 2-hole rubber stoppers (or side-arm Erlenmeyer flasks, just to make life easier, if you have them)
About 60 cm (24") of rubber/plastic dialysis tubing and glass eye droppers (for making air tight seals between the hoses and the stoppers)
Magnetic stir bar and a magnetic stirring hot plate
a pair of scissors
~ 500 mL of deionized water
A range of chemical indicators (as you have available in the lab)

10g each of the following solids:
- sodium bicarbonate
- sodium carbonate
- calcium carbonate
- calcium hydroxide
50 mL each of the following solutions:
- 0.1 M acetic acid
- 0.1 M hydrochloric acid
- 0.1 M sulfuric acid
Disposable plastic pipettes
Digital pH meter or pH probeware system with data collection
Gaseous CO₂ sensor or probeware system (optional)

Possible student-provided materials (purchased for under $3 per student - students may pool resources between groups)

Dry ice (purchased through instructor)
Various solid and liquid combustibles (fire to be managed with EXTREME caution)
Seltzer water

Procedure

If I told you step-by-step how to do it, where would the challenge be?

Ok, you, the teacher, need to have some idea how to do this, but there may be more than one way to accomplish these goals, so flex with your kids. Here is the method that inspired me to try this project.

Connect the pair of 2-hole stoppers together with the hoses and droppers (or connect the side-arms via hose). Only one hole on each stopper should be in use.
Pour 100 mL of the deionized water into one of the flasks. Gently place the stir bar in the flask and set the flask onto the stir plate. Set the stirrer to a low/medium pace (setting 3 or 4?).
Set up the pH meter/probe through in the solution. Slowly begin to add the sodium bicarbonate until the pH reads somewhere from 8.30 to 8.31 (if your meter is that sensitive). Now you should have a solution that can act as a pH buffer to carbonic acid when you introduce gaseous CO₂ into the atmosphere above the solution in the flask, thus simulating seawater.
In the empty flask, place about 1 g of dry ice (a pea-sized piece should be more than sufficient)
Now place the pH probe through one of the holes in one of the 2-hole stoppers. Place the CO₂ sensor in the free hole of the other stopper.
Plug both flasks lightly with the stoppers such the the pH meter is in the buffer and the CO₂ sensor is above the dry ice. Students should maintain a safe distance from the stoppers as pressure may build up if the stoppers are too tight.
Begin collecting data with the probeware. As the dry ice sublimates off gaseous CO₂ the pH of the buffer solutions should, ideally, stay constant for some time but begin to drop over time.

From this point, the students should have demonstrated that their buffer works as intended and the CO₂ system does as well. Controlling that absorption of CO₂ could happen in any number of ways, from adding extra one of the carbonate or bicarbonate compounds (or even hydroxide) to the buffer, introducing a freshwater plant like elodea (if students have purchased it), or even simply warming the buffer to make CO₂ less soluble.

Questions

Q: Create a conceptual model making a connection between CO2 emissions and marine organism calcification.
- As CO₂ levels rise, ocean pH will continue to drop.

- A: This will weaken the ability of many marine species to calcify as the acid will make calcium more soluble in the seawater, and thus more difficult to precipitate into exoskeletons.

Q: Explain in words, the connection between Atmospheric CO₂ levels and a change in ocean pH.
- As CO₂ dissolves in water, it reacts with water molecules to create carbonic acid. That acid will equilibrate with bicarbonate ion at the typical pH of seawater. As more CO₂ dissolves, it generates more carbonic acid, which releases more hydrogen ion, thus decreasing the pH.

Q: What effect will increased CO₂ levels have on the food web in the ocean?
- A: There are two major effects. As the CO₂ pushes pH level down, the shells of many calcifying marine species can suffer degradation and dissolution. For example, the shell of the "sea butterfly" below is shown in a solution with the ocean pH predicted for the year 2100. Because sea butterflies also happen to be prey to animals as diverse in size as krill to whales, loss of this and similar species could serious undermine an entire food web. However, and somewhat counterintuitively, many photosynthesizing plants that are not as pH sensitive will actually find benefit from the extra CO₂ dissolved in the water as it serves as the fundamental building block for glucose formation.

What effect will increased CO₂ levels have on human industries such as fisheries and tourism?
- Fisheries can be damaged directly as hatchlings and juvenile fish may be more vulnerable to pH anomalies than adults, especially if they are calcifying species. Any kind of marine food sourcing would be threatened. Also, as coral reefs are bleached, the reef ecosystems they support collapse. In tropical locations where dive tourism is a major sector of the economy, large numbers of people could lose their jobs.

Photos

Movies

I don't have any of my own videos yet, but here's some stuff YouTube has to offer:

References

Kroeker, K. J., Kordas, R. L., Crim, R. N. and Singh, G. G. (2010), Meta-analysis reveals negative yet variable effects of ocean acidification on marine organisms. Ecology Letters, 13: 1419–1434. doi:10.1111/j.1461-0248.2010.01518.x

Seawater carbonate chemistry

The Chemistry of Ocean Acidification

How Growing Sea Plants Can Help Slow Ocean Acidification

Ten Ways States Can Combat Ocean Acidification (and Why They Should)

Shells in Acid activity

An old lesson plan from NOAA, but pretty good - Lesson 3: Ocean Acidification

Ways to DO SOMETHING from the Revolution movie website

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