Water Planet Challenge

Electrically Speaking: Acid Bath! - Middle School

Introduction

Students often have preconceptions about how their actions can and do effect the environment. This lesson is focused on the way that human use of natural resources impacts the atmosphere and in turn the waters of the Earth, in particular the oceans. The ocean is the feature of the Earth that makes it a unique place where humans and other organisms can live. Since the Industrial Revolution humans have been using fossil fuels to provide for their energy needs. Burning fossil fuels release carbon dioxide into the atmosphere, and it has been absorbed by the oceans for the last two centuries changing the pH of the water. The previous lesson examined the physical and chemical effects of the addition of anthropogenic carbon on the oceans. This lesson will examine the effect of increasing acidity on the shells of organisms. Even the slightest changes in the ocean in turn have impact on the environment, biodiversity and human population.

Objectives

• Describe how everyday human activities produce pollutants that can be measured.
• Determine the affect pollutants have on the planet and the health of organisms on the planet.

Materials

• Computer with Internet access
• Library and/or classroom resources
• Science journal
• Sea shells (5 or 6 per group) or carbonate shell sand
• Water
• Distilled vinegar
• Plastic cups or containers
• Electronic balance

Vocabulary

• global warming – refers to an average increase in the Earth's temperature over time
• climate change – a result of the overall average increase in the Earth's temperature. This term encompasses all changes to the Earth’s climate, ecosystems, human health and society.
• anthropogenic carbon – carbon emitted to the atmosphere due to the activities of man and closely linked to current changes in the climate.
• environment – the habitats surrounding an area
• acidification – ongoing decrease in the pH of the Earth's oceans
• CO2 – carbon dioxide, the primary greenhouse gas Carbonization
• carbon cycle – the biogeochemical cycle by which carbon is exchanged between the biosphere, geosphere, hydrosphere, and atmosphere of the Earth.
• atmosphere – the layer of gases surrounding the Earth
• hydrosphere – the waters of the Earth
• biosphere – all regions of the Earth environs that house life.
• solubility – is the property of a solid, liquid, or gaseous chemical substance called solute to dissolve in a liquid solvent to form a homogeneous solution

Teacher Background

The ocean is an open system that receives energy from the sun and carbon dioxide from the air. The oceans are becoming more acidic because carbonic acid forms when carbon dioxide dissolves in water. The oceans are warming because carbon dioxide in the air is a greenhouse gas that causes the air to hold more heat. That in turn causes the oceans to release less heat to the air. Increasing acidity and temperature are just two of the changes our oceans are experiencing. More specifically, when carbon dioxide (CO2) reacts with seawater lowering the pH, it also reduces the availability of carbonate ions which play an important role in shell formation of marine organisms such as corals, marine plankton, and shellfish. This phenomenon is commonly called ocean acidification. The acid causes erosion of the shells and coral skeletons and there is less calcium available for organisms to build new shells. This happens because a secondary reaction decomposes the calcium carbonate in shells to produce bicarbonate ions (HCO3-). This process acts as a slight buffer against acidification by absorbing excess hydrogen ions, but at a cost to living systems. The buffering effect is slight and diminishes as the acidification increases. Scientists are still building a model incorporating all these variables in order to better understand the extent of the impacts anthropogenic carbon from the burning of fossil fuels has on our oceans living systems.

Some of the smaller calcifying organisms are important food sources for higher marine organisms resulting in disruption of food chains. Declining health in coral reefs due to increases in temperature and decreases in carbonate ion would have negative impacts on tourism and fisheries. Abundance of commercially important shellfish species may also decline and negative impacts on finfish may occur. This rapidly emerging scientific issue and possible ecological impacts have raised serious concerns across the scientific and fisheries resource management communities.

The addition of anthropomorphic carbon dioxide caused by our burning of fossil fuels has intensified the greenhouse effect shown in the following diagram. The Earth is in radiative balance, the sun provides radiant energy to the Earth in turn the Earth radiates or reflects radiation out into space at an equal rate. There is evidence that the build up of heat trapping gasses such as CO2 has increased the temperature of the Earth’s radiative balance during the last 100 years.

http://coralreefwatch.noaa.gov/satellite/oa/description/oaps_intro_oa.html

The effects of this increasing pH can have multiple effects on life in the ocean. True the algae and sea plants may benefit from increased CO2 using it for photosynthesis. The animal life can be affected several different ways. The creation of carbonic acid is dissolving the shells of shellfish and corals that are made of calcium carbonate. The acid is also reducing the available molecules these animals use to build their shells. Studies are also being conducted concerning the effect of lower pH on the reproduction rates of sea urchins, oysters and corals. In the event that these organisms die out it will disrupt the marine food chains and human fisheries.

Additional sources:
Measuring and monitoring the amounts of CO2 mixing in the oceans: http://www.oar.noaa.gov/research/2007/ocean_acidity.shtml
Explaining the chemical interactions of CO2 once it has entered the oceans: http://coralreefwatch.noaa.gov/satellite/oa/description/oaps_intro_oa.html
Coral reefs are affected by ocean acidification: http://www.usgs.gov/newsroom/article.asp?ID=1847
http://oceanacidification.wordpress.com/2011/01/17/coral-reef-conservation-ocean-acidification/

Corals are under a double threat, acidification and increased temperature. Though higher temperatures may return some of the dissolved CO2 to the atmosphere, the increased temperatures cause coral bleaching:
http://www.climatewatch.noaa.gov/2010/articles/hope-in-the-face-of-a-caribbean-coral-crisis
http://www.stanford.edu/group/microdocs/coralbleaching.html
For basics on corals: http://pbs.bishopmuseum.org/Oman-coral-book/Chap1/CorBkCh1.htm

Engage

Ask students to look at the 3 maps and make observations. Based on the information provided in the maps what would they predict the conditions would be when they are 80 years old? How does the failure of the coral reef habitat impact your lifestyle? Answers may include: there will not be any coral reefs, the reef may change to survive, there will not be as many fish.

Caption: The three maps show model data of how the availability of calcium carbonate is predicted to decrease over the next century at a depth of 10 meters in the ocean—where most corals occur. Blue indicates surface waters are sufficiently saturated with calcium carbonate; organisms have enough material to build their protective shells. Areas that are deep red are expected to be sufficiently acidic to dissolve shell-building organisms. Graph based on models by James Orr of the Laboratory for the Sciences of Climate and Environment in Paris. Image courtesy of the NOAA Environmental Visualization Laboratory. http://www.climatewatch.noaa.gov/2009/articles/an-upwelling-crisis/2

Explore

Ask students: Have you ever noticed the lifeguard at the pool testing the water every hour? Or have you ever had an aquarium that required checking the water? What are they checking for? Answers may include: pH, temperature, acid, chemicals such as chlorine, urine. One of the factors they are checking is the pH of the water.

Review with students the pH scale. The scale ranges from 0 to 14 with 7 being neutral. Water that measures below 7 is more acidic, while above 7 is more basic or alkaline. the natural pH of water is considered to be 7 though that is not always true. Explain to students that ocean water is normally slightly basic. Refer to the last activity when they tested the pH of different water samples, and explain that increased carbon dioxide is causing ocean water to have a lower pH or to become more acidic.

Ask: what could happen in a pool or aquarium if the pH was too acidic or too basic? Answers will vary: the animals will die, it will burn their skin, they will not be able to see.

Help students review the ways the pH of water can be changed. Remind them that the increase of burning fossil fuels has increased the amount of carbon dioxide in the atmosphere and oceans.

Testable Question

How does more acidic water affect ocean animals with calcium carbonate shells or skeletons?

Materials

• science journal

• sea shells (try to make them of similar species and size, 5 to 6 per group), thin shells work well or carbonate sand, if available

• water

• distilled vinegar

• clean plastic containers or beakers

• pH paper strips of meter

• tongs

Procedure

1. Draw, label, and make observations of each seashell, include mass, color, size, thickness, strength (students can place a book on top of the shell to determine the strength and other measurements.

2. Label the cups or containers with the strength of the solution to be used.

3. Place a shell into each container or a predetermined amount of sand.

4. Teacher should make the solutions. Make different strengths of acid solutions (pH 7, pH 6, pH 5, pH 4, pH 3). Using distilled water and a pH paper or pH meter add distilled vinegar one drop at a time until the solutions are the desired pH.

5. Pour the solutions 200 ml each into the correct cup covering the shells. If 200 ml does not cover the shells or sand, more solution should be added. Remember to add the same amount to each container.

6. Allow the shells to sit in the solution for a day or more, record observation of the shells/sand and the liquid.

7. Using tongs, remove each shell from the container and make final observations. If using sand, make observations during the class period and students can leave the containers overnight and observe the next day.

Side Bar on Safety: Goggles and apron should be worn.

Analysis

Using evidence from the experiment, explain: what is the affect of the acid on marine animals with hard shells? Answers may include: Marine animals with hard shells depend on calcium carbonate to make their shells. As the oceans become more acidic, their shells become less massive, thinner and weak.

Explain

Show the video from American Museum of Natural History - Acid Oceans This 6-minute video is about an experiment scientists are conducting concerning the effect of ocean acidification on sea urchins.

If you're an ocean creature with a hard shell—like a sea urchin, hermit crab, or coral polyp—you prefer ocean water with a pH of about 8.2. This chemistry makes it easy to assemble your armor from carbon-based building blocks dissolved in the ocean. Since the industrial age, though, the ocean's pH has become more acidic from absorbing the greenhouse gas carbon dioxide from the air, dropping to 8.05 on average. Biologists like Gretchen Hofmann are realizing that this tiny change is hampering the development of hard-shelled marine life, leaving it more vulnerable to environmental stressors.

Adapted from http://www.amnhblogs.org/content/science-bulletins-acid-oceans

1. Using evidence from the experiments you have performed explain where the carbon dioxide in the ocean is coming from and how has the CO2 absorbed by the ocean changed its chemistry (products, pH).
(Answers may include: The increase in carbon dioxide has decreased the ocean’s pH from 8.2 to 8.05 on average, making it more acidic because when CO2 dissolves in water it also reacts with water to form H+ and HCO3- ions. The free H+ then reacts with carbonate ions in ocean water to form more HCO3-. The result is less CO3- ions which are required to form shells or CaCO3 )
2. Once the acid has formed in the water, what does it do to shells? Explain the processes involved.
Students may read this article to help answer this question.
http://www.epa.gov/acidrain/effects/surface_water.html#a2
3. Explain the effect increasing acidification of ocean water can have on animal species. Answers will vary: Burn their skin, dissolve their shells and skeletons, kill their food sources.
4. Elaborate using evidence from the experiment and research on what impact do you think a more acidic ocean would have on the ocean food web. Describe the consequences in detail using an actual food web. Answers may include: The warming and acidified ocean would impact organisms, such as shrimp, lobsters, crabs, clams, oysters and coral, which depend on calcium carbonate to develop their shells. Changes in the size or abundance of these organisms would affect the humans and marine life that depend on them for food.

Evaluate

Explain how your use of electricity is causing stress to ocean animals. Use evidence you have collected in the other activities from this website. Compare how we use and produce electricity, the emissions burning fossil fuels releases into the atmosphere, and how the ocean play a part in cleansing the atmosphere, to the effect on ocean ecosystems.

Elaboration

Students may take salt water add acid and compare the effect on shells in fresh verses salt water.

Students may test the difference effects of acid on shells in water of different temperatures.

Share the following diagram with students. Ask them to use the diagram to explain how the carbon cycle is involved in the problem of ocean acidification.

Additional websites:
http://www.climatewatch.noaa.gov/2009/articles/an-upwelling-crisis
http://www.climatewatch.noaa.gov/2009/videos/origin-and-impacts-ocean-acidification2
http://www.climatewatch.noaa.gov/2009/videos/origin-and-impacts-ocean-acidification-part-3
http://www.myfootprint.org/
http://www.pmel.noaa.gov/co2/OA/OA2.jpg
http://www.pmel.noaa.gov/co2/OA/A_Sea_Change_Excerpt.mov

ESS Core Idea 4: Human activities are constrained by and, in turn, affect all other processes at Earth's surface. [Human Interactions with Earth] Grades 6 - 8
ESS4.D: Global Climate Change Sub-question: How will global climate change affect humans? Climate change, driven by both natural and human activities, has large consequences for all of Earth's surface systems, including humans. Humans can take actions to reduce climate change and its impacts.
How do human activities alter Earth's climate?
Humans alter global climate patterns by burning fossil fuels, releasing chemicals into the atmosphere, reducing forest cover, and by the rapid expansion of farming, development, and industrial activities.
Global climate change is causing changes in many biological systems, including a decrease in biodiversity and a diminishing of the capacity of some environments to support life.
LS Core Idea 3:Organisms and populations of organisms obtain necessary resources from their environment which includes other organisms and physical factors. [Ecosystems: Interactions, Energy, and Dynamics]
LS3.C: Ecosystems Dynamics, Stability, and Resilience
Sub-question: What happens to organisms and ecosystems when there are changes in the environment? Ecosystems dynamics can result in changes in the number and types of organisms and the survival, migration, and extinction of species.
What happens when components of ecosystems change? Ecosystems are dynamic in nature; the number and types of organisms and populations of organisms in ecosystems have continuous fluctuations over time.
Disruptions to the physical (abiotic) or biological (biotic) components of an ecosystem impact other components of an ecosystem.
Biodiversity, the variety of species, is used as a measure of the health of an ecosystem. LS Core Idea 4: Biological evolution explains the unity and diversity of species. [Biological Evolution: Unity and Diversity]
LS4.D: Biodiversity and Humans
Sub-question: What is biodiversity and how do humans affect it and how does it affect humans? The diversity of genes, species, and ecosystems provide humans with renewable resources such as food, energy, and medicines. The resources of biological communities should be used with in sustainable limits, but in many cases the human impact on them is exceeding sustainable limits.
What happens when the diversity of life changes?
Changes in biodiversity can influence humans’ resources such as food, energy, and medicines as well as ecosystem services such as purification and recycling.
Physical Science (PS) Core Idea 1: Macroscopic states and characteristic properties of matter depend on the type, arrangement and motion of particles at the molecular and atomic scales. [Structure and Properties of Matter]
PS1.B: Properties of Matter
Sub-question: How can you distinguish one substance from another? All substances have characteristic measurable properties that depend on the conditions under which they are observed. These properties depend on atomic substructure but do not persist at the atomic level.