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The Effect of Acid Rain on Marigold Plants (page 3)

based on 155 ratings
Author: Ryan T.

Results

Note: Since the acidic solutions were added beginning on Day 3 to allow plants to adjust to the replanting, the changes were compared to Day 3.

Height Changes (Growth):

The acidic watering solutions did have an effect on the plants. See the chart below for the effect on the plant growth. As the acidity of the water increased (the pH level went lower), the growth rate declined dramatically. The initial changes in pH showed steadily increasing growth declines with significant declines at the 3.75 and lower pH. While there is a high standard deviation, this trend still shows in the detailed graphs shown in the log book.

Note: Lower pH means higher acidity.

GROWTH CHANGES
Watering Solution

Average Growth (Mean)

Standard Deviation from Mean (Average)

% Growth Change from pH 6 solution

Median Growth
1 - pH 6
.72
.60
 
.6
2 - pH 5.5
.66
..82
- 8.3%
.3
3 - pH 4.3
.62
.61
- 13.9%
.3
4 - pH 4.0
.53
1.03
- 26.4%
.3
5 - pH 3.75
-.05
1.23
-169.4% - almost dead
-.3
6 - pH 3.2
-8.3
2.52
-1252.8 dead
-9.2
 
Flower Changes:

The number of flowers declined once the acidity of the water reached a pH below 3.75. The plants in the pH of 4.0 - 6 showed an increase in flower growth from the control, pH 6. While there is a high standard deviation, this trend still shows in the detailed graphs in the log book

FLOWERING CHANGES
Watering Solution

Average Change in Number of Flowers

Standard Deviation from Mean (Average)

% Change from Control pH6
Median
1 - pH 6
-1.4
.55
 
-1
2 - pH 5.5
-.6
.55
+57.1
-1
3 - pH 4.3
-.8
.84
+42.9
-1
4 - pH 4.0
-.4
1.14
+71.4
0
5 - pH 3.75
-1.4
1.14
0
-1
6 - pH 3.2
-1.88
.82
-34.37
-2
 
Buds/Sprouts Changes:

The number of buds or sprouts declined in growth as soon as the acidity of the water increased (pH becomes lower). The counts decreased at an increasing rate until the highest acidity level resulted in no sprouts or buds at all. While there are high standard deviations, this trend still shows in the detailed graphs in the log book.

SPROUTS/BUDS CHANGES
Watering Solution

Average Change in Number of Sprouts

Standard Deviation from Mean (Average)

% Change from Control pH 6 solution

Median
1 - pH 6
3.8
1.87
 
4
2 - pH 5.5
3
1.41
-26.7
2
3 - pH 4.3
1.6
1.67
-57.9
2
4 - pH 4.0
1
1
-73.7
1
5 - pH 3.75
1.4
3.2
-63.2
3
6 - pH 3.2
-2.75
.96
-475
.96
 
Because sprouts and buds turn into flowers, it is important to observe the combination of those changes. There is a decline in growth as soon as the acidity of the water increases from pH 5.5 (pH of average rainwater without acid rain conditions). The counts decreased at an increasing rate until the highest acidity level resulted in no flowers, sprouts or buds at all. The standard deviations are high because there was a wide spread around the average, but the detailed graphs show the trends are still there.

FLOWERS AND SPROUTS COMBINED CHANGES

Watering Solution

Average Growth (Mean)

Standard Deviation from Mean (Average)

% Growth Change from pH 6 solution

Median
1 - pH 6
2.4
1.82
 
3
2 - pH 5.5
2.4
1.52
0
2
3 - pH 4.3
.8
2.17
-66.7
1
4 - pH 4.0
.6
.55
-75
1
5 - pH 3.75
0
4.3
-100
2
6 - pH 3.2
-4.75
1.71
-298
-4.5
 
In addition, by observing the plants I could see that the overall health of the plants watered with higher acidity water were not as healthy as the plants watered with lower acidity water. The plants were wilting, the flowers were droopy, the colors dulled, the sprouts didn't open, and the leaves began to turn brown. The plants showed signs of unhealthiness (including shriveling flowers, wilting, etc.) by day 4 with pH 3.2 ending in death, day 8 with pH 3.75, and day 10 with pH 4.3 and pH 4.0. No change was seen with pH 5.5.
 
 

Conclusions

  1. My hypothesis that if I increase the acidity in the watering solution (similar to acid rain), then the rate of growth of the Marigold plants will decrease was correct. After 8 days of differing pH levels in the water, the rate of growth slowed by 8.3% with the first increase of acidity, 13.9% with the second increase of acidity, 26.4% in growth decrease for the third increase in acidity and then for the last two levels of acidity, the growth was extremely negative at a 169.4% decrease for pH 3.75 and a decrease of 1252.8% in the highly acidic pH 3.2 as the plants began to die. The highest acidity level solution caused the plants to die after only 1 day of watering with the high acid water. Starting with an acid level of 4.3, I saw the plants starting to die by day 10 (as shown by their shriveling and wilting) and start to die earlier with each increase in acid level.
  1. My hypothesis that for each 1pH change in acidity, the plants will grow at a rate that is 25% less than normal, eventually resulting in the death of the plant was partially incorrect. From pH of 6 to the pH of 4, there was a decrease in growth of 26.4%. It initially took 2 pH level changes to register a 25% decline in growth. The first ½ pH increment resulted in a growth change of 8.3%, or a 16.6% rate for 1 pH. The rate of change was similar by pH increment until pH4. The rate of decline in growth was much higher than 25% at that point. In fact, the result of acid rain was even worse than expected, resulting in death of all plants at pH of 3.75 and lower (higher acidity levels). So yes, the increased acidity level did result in plant death but the rate of decline was not in a steady line. The decline of growth started off slower than I expected and then increased much more than I expected.
  1. My hypothesis that the flowers will show measurable signs of unhealthiness including a decrease of 10% at each 1pH increase in the acidity in the number of flowers, a 10% decrease in the amount of sprouts, and plant death at the most acidic pH was mostly incorrect, although my anticipation of a negative effect was correct. For flowers alone, my hypothesis was incorrect. Acidic solutions up to a pH of 3.75 is actually good for the plant's flowers, then at a pH of 3.2, they declined by 34.37%. For sprouts/buds growth, my hypothesis was incorrect because I understated the negative effects of an acidic solution. Instead of a 10% decline, they declined beginning at a decrease of 27% and ended in a decrease of 475% with the highest acidic solution.  Most importantly, if you look at new growth (buds and sprouts) combined with the flowers, instead of a steady 10% decline as I had predicted, the results show a 67% decline beginning at pH of 4.3, and continuing to rise up to a decline of 298%, eventually leading to the death of the plant. My hypothesis about plant death was correct. The plants showed signs of unhealthiness (including shriveling flowers, wilting, etc.) by day 4 with pH 3.2 ending in death, day 8 with pH 3.75, and day 10 with pH 4.3 and pH 4.0. No change was seen with pH 5.5.
Improvements:

If I were to improve on this experiment, I would observe the plants for another 7 days. I would also spend more time creating more even differences in pH levels. It took a lot of time to get the desired result of pH. Now that I know the dramatic effects of the changes in pH level, I would like to have even greater accuracy, using a very high caliber scientific pH meter rather than pH strips which may leave room for judgment on the colors. I would also expand this project to include plants and animals, as in a lake environment.

Why is studying the acid rain effects on plants important? 

Acid rain is a complex environmental problem which affects the United States and many other countries around the world. Since acid rain and its effects have dramatically increased over the last 30 years, we need to study its effect so that we can inform the public. We can then promote actions to stop acid rain, including education, conserving energy, and minimizing the miles driven by cars and trucks by using alternative "clean" transportation such as bikes or walking. We can encourage the government to pass laws to limit nitrogen oxide and sulfur dioxide production, increase research funding for alternative energies and ways to decrease coal pollution. Finally, we can inform the public of car pollution and encourage low emission vehicles.

We can sponsor uniform acid rain measurement stations, like the ones set up by the United States Geological Service, all over the world. We should not only measure the acid rain levels, but collect data on large sections of trees and plants so we can more accurately gauge the effects of small changes in acid rain on the environment. This will help us quantify the financial impact it has on industries and the environment so we can justify some corrective actions or buffering measures to lower the acidic content of areas and support limits on industry. The international treaties currently in place between the United States and most European countries and Canada should be revised based upon these studies and enforcement actions installed. We have made some steps forward with the implementation of the Acid Rain Program established by the Clean Air Act Amendments of 1990 that implemented a program to use both regulatory and market based approaches to controlling air pollution. We need to continue to measure the impact and change the programs as needed.

Questions for Future Research

After completing this project, I would like to look into corrective measures for high acidity conditions. This would include looking into buffers, or things that would offset the increase in pH such as nitrogen and sulfur which can have an effect on the pH levels of rainfall. Freshwater lakes commonly are slightly basic. pH's in the range of 6.5 to 8.2 are best for most plants and animals, and below 5.0 is lethal to many fish. A lake's ability to buffer acid water is a function primarily of the concentration of carbonate (CO3) and bicarbonate (HCO3) ions. In areas with limestone (CaCO33) bedrock, surface waters have high concentrations of carbonate and bicarbonate and therefore are able to resist change in pH. The pH of a well-buffered lake does not change dramatically following a storm or snowmelt period because the acidity becomes neutralized by these ions. In regions where the bedrock is granite, the soils and surface waters are naturally low in alkalinity. One such region is the Adirondack Mountains, where approximately 20% of the lakes are too acidic to support fish life. Soil pH can be raised by adding limestone, wood ashes, cottonseed meal, sulfur or pine needles. Another approach to restoring acidic lakes is to add lime to the lake itself, to the streams flowing into it, or to the watershed land. This can be simulated in an experiment using baking soda (NaHCO3), horticultural lime, or a stomach antacid such as Tums, which is made up of CaCO3. Some salts in soil may also act as buffering agents. 

In addition to testing the effectiveness of buffering agents, I would be interested in testing different types of soil to see if the type of soil effects acidity.

I would also like to research the acid rain effects on humans. Are there any health problems caused by acid rain? Does it affect our sources of food, water and air?

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