Investigating the effect of acid rain on seed germination

Effects of Acid Rain Carolina Distance Learning

Investigation Manual

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Table of Contents

Overview ......................................................................................................... 4

Objectives ....................................................................................................... 4

Time Requirements ........................................................................................ 4

Background .................................................................................................... 5

Materials .......................................................................................................... 9

Safety ............................................................................................................. 10

Preparation ................................................................................................... 11

Activity 1: Germination in an Acidic Environment ................................ 12

Activity 2: Buffering Capacity of Soil ........................................................ 13

Disposal and Cleanup ................................................................................ 14

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Overview

In this series of hands-on activities, students will learn about the biological,

environmental, and chemical mechanisms that are associated with acid rain. First,

determine the pH of unpolluted rain and observe the effect of acid rain on seed

germination. Then investigate the buffering effects of different types of soil in the

student’s locale.

Outcomes

 Interpret the effect of acid rain on the germination of lettuce seeds.

 Explain how soil composition can mitigate the effects of acid deposition.

Time Requirements

Preparation ............................................................................................. 30 minutes

Activity 1 .................................................................................................45 minutes + 3 days

Activity 2 .................................................................................................90 minutes

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Background

Acid Deposition

Despite significant reductions in air pollutant emissions over the past 30 years, acid

deposition remains a threat to human-made structures, aquatic organisms, forests, and

human health. The process of acid deposition begins when gaseous sulfur dioxide and

nitrogen oxides (nitrogen monoxide, nitrogen dioxide, and dinitrogen monoxide) are

released into the atmosphere and react with oxygen and water to form sulfuric and

nitric acids as well as sulfate and nitrate salts. This is most commonly encountered as

acid rain, but may also include acidic snow, clouds and fog.

2SO2(g) + O2(g)  2SO3(g)

SO3(g) + H2O(l)  H2SO4(aq)

H2SO4(aq) + 2H2O(l)  SO4 2–(aq) + 2H3O+(aq)

NO, NO2, N2O(g) + O2(g) + H2O(l)  HNO3(aq)

HNO3(aq) + H2O(l)  NO3(aq) + H3O+(aq)

The Hydrologic Cycle

As precipitation falls, carbon dioxide present in the atmosphere dissolves in the water

and reacts to form carbonic acid, H2CO3, which is a weak acid. For this reason,

unpolluted rainwater is acidic, with a pH value around 5.6.

CO2(g) + H2O(l)  H2CO3(aq)

When precipitation reaches the ground, it runs off into surface water or infiltrates the

soil. The water that infiltrates the soil percolates through permeable rock and into

groundwater. Both surface water and groundwater proceed to the ocean. Water

returns to the atmosphere when surface water or ocean water evaporates and plants

transpire.

Areas Affected by Acid Deposition

The major sources of sulfur dioxide emission in the United States are coal-burning

electric utilities (70%), whereas the major sources in Canada are industrial plants

(60%). Emitted gases rise into the atmosphere, where they are carried east and

northeast by prevailing westerly winds. These winds can disperse the pollutants

hundreds of miles from their source. In fact, most of the acid deposition that affects the

northeast United States and eastern Canada originates in the Midwest region of the

United States. As these gases get carried by the winds, they react with oxygen and

water to form sulfuric and nitric acids, as well as sulfate and nitrate particles. Acid

deposition is a regional rather than global problem because of the limited force of the

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wind currents. Nevertheless, winds can carry air pollutants over political borders and

create tension between neighboring countries. For example, tensions ran high in the

late 1980s when it was found that air pollutants originating in the U.S. were being blown

into Canada.

Major areas affected by acid deposition include the northeastern United States and

southeastern Canada. Acid deposition in these regions is intensified due to the large

number of factories and coal-fired power plants in the Midwest United States. Areas of

Central Europe and Scandinavia are also affected by acid deposition due to

directional winds carrying pollutants from factories in Great Britain and other European

countries. Large areas of Asia, including India and China, are also affected by acid

deposition due to their reliance on coal-fired plants for energy and industrial production

needs.

Effects of Acid Deposition

Acid deposition affects plants, human-made structures, surface water, aquatic

organisms, and human health. Acid deposition damages the leaves and bark of trees,

impairing the ability of trees to photosynthesize, leaving them vulnerable to insects and

disease. The acid burns leaves by removing the outer coating, leaving brown spots.

Acid deposition also leaches nutrients, such as calcium and magnesium from the soil,

depriving already weakened trees of essential minerals. Acid also releases into the soil

toxic aluminum ions that were once attached to minerals, potentially damaging plant

roots. Trees at higher elevations are especially susceptible, because cloud vapor can

be 10 to 100 times more acidic than acid rain and can bathe trees in acid for days at a

time. As water evaporates from the acidic raindrops on a plant, the acidity of the

raindrops can increase.

Acid deposition can deteriorate certain materials and corrode certain metals. Many

ancient statues and buildings are made of marble and limestone, two forms of calcium

carbonate (CaCO3). The Colosseum in Rome and the Taj Mahal in India both show signs

of degradation caused by acid deposition.

Perhaps the best-known effect of acid deposition is the acidification of surface water

and the resultant harm to aquatic organisms. As fish and amphibians develop, the eggs

are particularly sensitive to changes in pH. Although tolerance varies by species, fish

eggs generally will not hatch in water with a pH of 5 or lower. Suboptimal pH is not

necessarily lethal, but it often leads to lower body weight and smaller size, making fish

more vulnerable to predation and less able to compete for food. Acid deposition also

releases into surface waters aluminum ions that once were attached to minerals in

nearby soils. These ions stimulate excessive mucus formation in fish. This mucus clogs gills

and ultimately asphyxiates many kinds of fish. A decline in the number of pH-sensitive

organisms can significantly disrupt an ecosystem and seriously affect the food web.

Acid deposition affects more than just the pH of water. The influx of nitrogen from nitric

acid deposition into surface waters can lead to eutrophic conditions. Symptoms of

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eutrophication include toxic and non-toxic algal blooms, declines in the health of fish

and shellfish, and decreases in dissolved oxygen levels. Eutrophic conditions brought

about by anthropogenic sources such as acid deposition can greatly threaten the

biodiversity of aquatic ecosystems.

The U.S. Environmental Protection Agency (EPA) conducted a National Surface Water

Survey to determine how many lakes and streams were affected by chronic acidity

and the percentage of these waters that were chronically acidic due to acid

deposition. The survey revealed that acid deposition is responsible for approximately

75% of acidified lakes and 50% of acidified streams. The affected areas include the

Adirondacks, mid-Appalachian highlands, the upper Midwest, and high-elevation West.

In areas such as the northeastern U.S., where there is poor buffering capacity, some

lakes now have a pH lower than 5. Little Echo Pond in Franklin, New York, is one of the

most acidic lakes reported, with a pH of 4.2.

Some soils are and water systems are better able to resist changes in pH. Typically soils

with higher clay content (or water systems located where there is clay content in the

soil) are better able to resist the change in pH because of the chemical composition of

the soil. The chemicals act as a buffer, meaning that they react with the acid first, and

prevent an immediate change in the pH of the soil or water. This buffering, helps

prevent large changes in pH if there is only occasional acid deposition. If there is a

large amount, or continual acid deposition, the pH would still decrease, but typically

this will occur at a slower rate than locations without this buffer.

Acid deposition does not cause direct harm to people; however, the pollutants that

cause acid deposition can directly affect human health. Lung cancer, asthma,

bronchitis, and emphysema can be caused and/or aggravated by air pollutants. For

example, the prevalence of respiratory ailments is 50% higher in the most polluted areas

of Poland, Hungary, and the Czech Republic than in cleaner areas of those countries.

Senior citizens, children, and people with weakened immune systems are advised to

stay inside during times of peak air pollution in many metropolitan cities.

Solutions

Title IV of the Clean Air Act Amendments, enacted in 1990, contains provisions to

regulate the emissions of sulfur dioxide and nitrogen oxide compounds. The EPA

established the Allowance Trading System in 1995. Under the auspices of this program,

regulated companies are allocated permits, called allowances, which allow them to

emit 1 ton of sulfur dioxide per allowance. The allowances may be used in the year

allocated or saved for future use. Companies can even buy, sell, or trade allowances.

Nitrogen oxides are controlled by a rate-based regulatory system that sets a limit on the

pounds of nitrogen oxides per million British thermal units (lbs/mmBTUs) emitted by every

power plant’s boilers.

One way coal-fired power plants can reduce sulfur dioxide emissions is to burn coal

with lower sulfur content. Low-sulfur coal contains 0–1% sulfur, and high-sulfur coal

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contains 2–4% sulfur. Sulfur dioxide emissions can also be reduced through the

installation of wet scrubbers at coal-fired power plants. Though costly to install at

existing power plants, scrubbers can remove 80–95% of emitted sulfur dioxides. Another

method, fluidized bed combustion, creates an environment in which combustion can

occur at a lower temperature and flue gases come into contact with sulfur-absorbing

materials. Lower amounts of nitrogen oxides are formed at lower combustion

temperatures. Sulfur-absorbing chemicals, such as limestone, then capture the sulfur

oxides before they are released into the environment. This process reduces emissions of

sulfur oxides by approximately 90% and nitrogen oxides by 15–35%.

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Materials

Included in the materials kit:

Bogen Universal Indicator, 15 mL 1

Bogen Universal Indicator Chart 1

Petri dish 4

Vinegar, 120 mL 1

Filter paper 4

Lettuce seed pack 1

Needed from the equipment kit:

Plastic cups 4

Pipets 5

Graduated Cylinder, 100-mL 1

Needed, but not supplied:

Water, Tap

Samples of soil of 3 types

Reorder Information: Replacement supplies for the Effects of Acid Rain investigation

can be ordered from Carolina Biological Supply Company, kit 580803.

Call 1-800-334-5551 to order.

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Safety

Wear your safety eyewear, gloves, and

lab apron at all times while conducting

this investigation.

Read all of the instructions for this laboratory activity before beginning. Follow the

instructions closely and observe established laboratory safety practices, including

the use of appropriate personal protective equipment (PPE) described in the Safety

and Activity sections.

Bogen Universal Indicator is flammable. Keep this chemical away from

any heat or flame sources.

Bogen Universal Indicator can cause damage to organs if ingested.

Do not eat, drink, or chew gum while performing this activity. Wash your hands with

soap and water before and after performing the activity. Clean up the work area

with soap and water after completing the investigation. Keep pets and children

away from lab materials and equipment.

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Preparation

Prepare the vinegar (0.88 M acetic acid) dilutions and the simulated acid rain solution.

This method of solution preparation is known as a serial dilution. This is a step-wise

process and typically the just prepared solution is used to create the next more dilute

solution.

1. Mix 20 mL of vinegar and 80 mL of tap water in the 100-mL graduated cylinder to

create 100 mL of 0.18 M acetic acid solution.

2. Pour the 0.18 M solution into a plastic cup, and label the plastic cup ‘0.18 M acetic

acid’.

3. Rinse the graduated cylinder with distilled water.

4. Pour 10 mL of the 0.18 M solution into the graduated cylinder.

5. Add 90 mL of tap water to the graduated cylinder.

6. Pour the solution into a different plastic cup.

7. Label the cup ‘0.018 M acetic acid’.

8. Rinse the graduated cylinder with water.

9. Pour 10 mL of the 0.018 M solution into the graduated cylinder.

10. Add 90 mL of tap water to the graduated cylinder.

11. Pour the solution into a different plastic cup.

12. Label the cup ‘Simulated acid rain’. This solution is 0.0018 M acetic acid.

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Activity 1: Germination in an Acidic Environment

For this activity, the higher-concentration acetic acid solutions will be used to simulate

the effect of continual acid precipitation on soil, leading to pH values lower than those

resulting from just a single occurrence of acid rain.

1. Place 1 piece of filter paper into 4 separate petri dishes.

2. Label one petri dish ‘tap water’.

3. Label the remaining 3 petri dishes with the concentrations of the different acetic

acid solutions.

4. Starting with distilled water, add ~7 mL of each solution to its respective dish on top

of the filter paper. Go from lowest concentration to highest concentration (i.e.,

simulated acid rain  0.18M).

5. Drain any excess liquid into a sink.

6. Place 20 lettuce seeds in each petri dish, on top of the saturated filter paper. Cover

each petri dish with a lid.

7. Place the covered petri dishes in a room-temperature well-lit location where they

will not be disturbed.

8. Observe the seeds in the dishes for 3 consecutive days. In Data Table 1, record the

total number of seeds that have germinated each day. Germination has occurred

with the seed coat splits and the first root begins to emerge from the seed.

9. Continue with Activity 2 while waiting for seeds to germinate.

Data Table 1

Day 0 Day 1 Day 2 Day 3

Tap Water

Simulated Acid

Rain

0.018 M Acetic

Acid

0.18 M Acetic

Acid

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Activity 2: Buffering Capacity of Soil

For this activity collect small soil samples of 3 different soil types. For example, clay,

sand, topsoil, etc. You will test to see how well each soil type resists changes to its pH

when exposed to acidic conditions.

1. Using your graduated cylinder, measure 25 mL of tap water and pour it into a 250-

mL beaker. Rinse the 100-mL graduated cylinder with tap water.

2. Add 10 drops of Bogen Universal Indicator to the beaker of tap water. Record the

initial color in Data Table 2.

3. Add approximately 30 mL of 0.018 M acetic acid solution to the graduated cylinder.

4. Use the pipet to add 5 mL of 0.018 M acetic acid. Swirl the beaker after each 5 mL

addition until the color remains consistent. Record the color of the solution in Data

Table 2.

5. Continue adding acetic acid in 5 mL increments until a total of 15 mL has been

added. Be sure to record the color of the solution after each addition.

6. Rinse the beaker with tap water into the sink.

7. Layer loosely at the bottom of the 250-mL beaker approximately 1 cm of the first soil

sample.

8. Using your graduated cylinder, measure 25 mL of tap water and pour it into a 250-

mL beaker. Rinse the graduated cylinder with tap water.

9. Add 10 drops of Bogen Universal Indicator to the beaker of tap water and the soil

sample. Record the initial color in Data Table 2.

10. Add approximately 30 mL of 0.018 M acetic acid solution to the graduated cylinder.

11. Use the pipet to add 5 mL of 0.018 M acetic acid. Swirl the beaker after each 5 mL

addition until the color remains consistent, you may need to let the soil settle before

you can see the color. Record the color of the solution in Data Table 2.

12. Continue adding acetic acid in 5 mL increments until a total of 15 mL has been

added. Be sure to record the color of the solution after each addition.

13. Empty the beaker into the sink, being careful not to pour the soil down the drain. Put

excess soil in the trash.

14. Repeat steps 8 – 13 for the additional 2 soil samples.

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Data Table 2

Initial Color 5 mL Color 10 mL Color 15 mL Color

Tap Water

Sample 1:

Sample 2:

Sample 3:

Disposal and Cleanup

1. Dispose of solutions down the drain with the water running. Allow the faucet to run a

few minutes to dilute the solutions.

2. Lettuce seeds and filter paper can be disposed of in the trash.

3. Rinse and dry the lab equipment and return the materials to your equipment kit.