As atmospheric carbon dioxide levels increase, the checks and balancesthat stabilize our planet's climate are compromised. Some scientistsbelieve that we can regain stability and prevent global warming byincreasing the flow of atmospheric carbon dioxide into Earth's oceans.At increased oceanic carbon dioxide levels, phytoplankton would take upmore of this dissolved gas. The carbon processed by these plants wouldbe "fixed" during photosynthesis, and locked into "sinking" organiccompounds that do not affect climate.
Testing the Waters
Bromothymol blue is a pH indicator solution that is often used to measure the acid/base nature of fish tanks. When drops of this colored solution are added to aquarium water, the dyed liquid undergoes a color change depending upon the acid concentration of the sample. In this activity, you'll use this indicator solution to assess changes in the carbon dioxide concentrations of water as reflected in pH shifts.
StrawBromothymol blue (obtained from pet store)Three 250mL (milliliter) beakersSprings of aquarium plants (such as Elodea)Plastic wrapSafety gogglesFiltered aquarium water (bottled spring water will also work)
1. Fill a small beaker with filtered aquarium water (or bottled spring water).
2. Obtain a dropper vial of bromothymol blue. Observe its color.
3. Add several drops of bromothymol blue to the water. What happens to the appearance of the water?
4. Put on a pair of safety goggles.
5. Insert the end of a clean straw into the dyed water. Gently blow out a slow, but steady stream of bubbles. What happens? Does the appearance of the dyed water change? Observe the full change in color.
6. Repeat steps 1-5 using two clean beakers. This time, introduce only enough carbon dioxide to turn the water green.
7. Place several sprigs of aquarium plants in both beakers that now contain green-dyed water. Observe and record the appearance of the liquids.
8. Cover both beakers with plastic wrap.
9. Place one of the beakers in direct sunlight.
10. Place the other beaker in complete darkness.
11. Each day observe the condition of the plants and the appearance of the water. Record your observations over a week's time. At the end of this activity, rinse and return the plants to their original aquarium environment.
