Introduction:Phytoplankton (plants) and zooplankton (animals) impact the concentrations of dissolved gases like carbon dioxide (CO₂) and dissolved oxygen (DO) in marine environments. Through the process of photosynthesis, millions of phytoplankton in the ocean use the reactants carbon dioxide, water, and energy from the sun to produce sugar (glucose) and oxygen. Living organisms use the products of photosynthesis (glucose and oxygen) to respire and gain energy (ATP). As a result of respiration, water and carbon dioxide are released as byproducts. Photosynthesis and respiration remain in equilibrium as long as the populations of plants and animals remain in balance and conditions within the environment remain stable. A change in the abundance of organisms or the concentration of dissolved gases like carbon dioxide and oxygen will affect the chemistry in the ocean. This in turn affects the pH balance of seawater and impacts many biological processes. If the pH increases, it causes the water to become more “basic.” In other cases, if the pH decreases, then the water becomes more acidic. A drop of one pH unit corresponds to a 10-fold increase in the concentration of charged particles in the water, making it more acidic (Doney, 2006). The pH of seawater ranges from 8.0 to 8.3, meaning that the ocean is naturally somewhat basic. Changes in water chemistry of ocean ecosystems affects the health and survival of organisms over time.
pH and Carbon Dioxide The pH scale has values from (0 to 14) with 7 being neutral pH > 7 (alkaline) pH < 7 (acidic) pH of the ocean normally ranges from 8.1 to 8.4 at the surface pH is directly influenced by carbon dioxide levels
Plant Activity: Decreases acidity (higher pH values) increases O₂ and decreases CO₂ from the water through photosynthesis
Plankton and CO₂What impact do phytoplankton and zooplankton have on CO₂, DO and pH levels in marine environments?
A Partnership between California Current Ecosystem Long Term Ecological Research (CCE LTER) and Ocean Institute (OI) Beth Simmons, Education and Outreach Coordinator, CCE LTER, Scripps Institution of Oceanography, Christy Millsap, Teacher, Rancho Bernardo High
School, San Diego, California.
LESSON TWO
1
Materials:
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Hypothesis: Brine shrimp (animals) and Elodea (plants) will change the levels of carbon dioxide (CO₂) and dissolved oxygen (DO) values within the water sample under light and dark environmental conditions which will result in the alteration of the levels of pH of the water.
Procedure:
1. Obtain 4 sample bottles-label them as follows:
1-brine shrimp, light
2- Elodea, light
3- brine shrimp, dark
4- Elodea, dark
2. Fill all four bottles with deionized water to equal volumes.
3. Take initial values for CO₂ , DO, pH and temperature in all four sample bottles and record in data table.
4. Place the brine shrimp in vials one and three, an Elodea sprig in vials two and four, then seal tightly with duct tape.
5. Carefully place vials one and two in a water bath under a light. (Note: The water bath can be an aquarium filled with room temperature water).
6. Carefully place vials three and four in a water bath in the dark. The water bath can be an aquarium covered with a trash bag to maintain a dark environment and filled with room temperature water.
7. Leave all the sample vials for 24 hours. (Note: Create graphs for each of the variables measured ahead of
time. There will be graphs needed for CO₂ versus time, DO versus time, and pH versus time.)
8. In class the next day, remove each sample from the water baths. Remove covers and record CO₂, DO, pH and temperature values for each sample bottle in your data table. (Note: If you are running the experiment for five consecutive days, then recap the vials immediately after data are taken. Otherwise, dispose of the contents properly and clean out all sample bottles.)
4 sample bottles with lids Aqueous Carbon Dioxide (CO₂) probe or chemical test kit for CO₂
Deionized water (DI) Dissolved Oxygen (DO) probe or chemical test kit for DO
Water bath (large aquarium or container) pH probe or chemical test kit
Ultraviolet light or other grow light Elodea sprigs (2 small sprigs per group)
Thermometer or temperature probe Brine shrimp (2 shrimp per group - if shrimp are small add more per group)
Heavy duty trash bag (to darken aquarium) Duct tape
1. Create a graph comparing CO₂ concentrations over time and write a brief statement describing your findings. (Note: If you only completed one 24-hour period of observations, record your initial and final values over time.)
2. Create a graph comparing DO concentrations over time and write a brief statement describing your findings.
3. Create a graph comparing the pH values over time and write a brief statement describing your findings.
4. Why were the samples put in both light and dark environments? Explain.
5. Compare what happened to the levels of CO₂ over time in the dark and light brine shrimp vials and the dark and light Elodea vials.
6. Compare what happened to the levels of DO over time in the dark and light brine shrimp vials and the dark and light Elodea vials.
7. Compare the DO and CO₂ graphs to the pH graph. Explain your observations.
8. What is the relationship between the brine shrimp and respiration in the vials?
9. What is the relationship between the Elodea and photosynthesis in the vials?
10. What would happen to CO₂ and DO concentrations in the ocean if the number of phytoplankton (plants) decreased?
11. What would happen to the CO₂ and DO levels in the ocean if the number of animals increased?
12. If CO₂ levels became very high, what would happen to pH levels? What impact might this have on plants and animals living in marine environments?
Conclusion:
Formulate a thoughtful conclusion to this experiment written in paragraph form. The conclusion should consist of the following: a. What was the initial hypothesis of this research? b. Explain any possible errors that may have affected your experimental results. c. Explain your understanding of the exchange of dissolved gases within the ocean’s realm between plants and animals and the impact of these exchanges on the pH of the water. Evidence of your understanding should address the implications of an imbalanced pH in ocean water.
Plankton and CO₂What impact do phytoplankton and zooplankton have on CO₂, DO and pH levels in marine environments?
A Partnership between California Current Ecosystem Long Term Ecological Research (CCE LTER) and Ocean Institute (OI) Beth Simmons, Education and Outreach Coordinator, CCE LTER, Scripps Institution of Oceanography, Christy Millsap, Teacher, Rancho Bernardo High
School, San Diego, California.
LESSON TWO
4
Vocabulary:
acidic: a pH value below 7.
ATP: An organic compound that contains large amounts of energy.
phytoplankton: Microscopic algae that live in the water and produce their own food through the process of photosynthesis. Collectively, phytoplankton are the foundation of the marine food web.
zooplankton: Drifting marine animals either invertebrates or larval fishes. These organisms are grazers, feeding on phytoplankton or predators, which consume other organisms.
photosynthesis: Chemical process by which plants convert light energy into chemical energy (glucose) 6CO₂ + 6H2O + light energy → C6H12O6 + 6O2
respiration: Chemical process through which animals convert chemical energy (glucose) into ATP to fuel cells C6H12O6 + 6O2 → 6CO₂ + 6H2O + energy(ATP).
pH: A common measure of how acidic or basic a solution may be.
dissolved oxygen: (DO) oxygen dissolved in water.
carbon dioxide: (CO₂) a chemical molecule composed of two oxygen atoms and one carbon atom; it is essential for many biochemical and living processes.
glucose: (C₆H₁₂O₆) a sugar that serves as the main source of energy for most living things.
Additional Resources and Notes:
1. Aqueous Dissolved Oxygen and pH probes are available through a. Pasco scientific- http://www.pasco.com/
2. DO, CO₂, and pH chemical test kits can be obtained through La Motte- http://www.lamotte.com/pages/edu/index.html
3. Test kits, probes and other water sampling supplies can be obtained through Wards- http://wardsci.com/category.asp_Q_c_E_915_A_Water+Testing+and+Sampling
4. Brine shrimp may be purchased from local fish and aquarium stores or can be hatched. Information and purchasing can be found at http://www.brineshrimpdirect.com/Hatching-Brine-Shrimp-Cysts-c169.html
5. Doney, Scott (2006) The Dangers of Ocean Acidification , Scientific American, pgs. 58 - 65.
Extension: Besides acting as the first link in the food chain, phytoplankton are a very important part of ocean life. Phytoplankton play a role in acting as transporters of CO₂ from the atmosphere into the ocean. The direction of exchange (accumulation versus absorption) depends on how much is in excess and how much is absorbed by plankton. There is a constant exchange of CO₂ between the atmosphere and the oceans. Because of the large size of the ocean, and the occurrence of phytoplankton everywhere, the ocean is a sink for atmospheric carbon dioxide. What would happen if phytoplankton did not bring CO₂ from the atmosphere into the ocean?
Questions:
a. What might cause phytoplankton abundances to decrease?
b. If fewer phytoplankton existed, what might happen to atmospheric carbon dioxide?
c. What would the implications of decreased phytoplankton be for the ocean ecosystem?
Possible resources:
a. Satellite Images of Marine Phytoplankton Blooms http://geology.com/nasa/marine-phytoplankton.shtml#top
b. Hays, Graeme C., et. al. (2005) Climate Change and Marine Plankton, Trends in Ecology and Evolution, Vol. 20 No.6, pages 337 - 344.
c. Morello, Lauren (2010) Phytoplankton Population Drops 40 Percent Since 1950, Scientific American, July. http://www.scientificamerican.com/article.cfm?id=phytoplankton-population
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Phytoplankton’s Influence?
Figure 1. Satellite image of chlorophyll a concentrations (which acts as a proxy for plankton biomass) from October 6, 2002 off the coast of California. Reds indicate high concentrations and blues indicate low concentrations.
