Collaborators:
Camile Burkhardt, Hilda Kolawole, and Ben Tiffany
Introduction and Problem:
According to Thorpe, soil erosion is the movement of weathered rock or soil components from one place to another -- caused by flowing water, and wind. Although it is a natural occurring process, it can be expedited by human activity: overcultivation, deforestation, and construction. Soil erosion is a serious environmental problem, as it damages vegetation, leads to droughts, and interferes with the oxygen capacity and pH of water. A strong inverse correlation exists between the presence and type of ground cover -- especially vegetation -- that covers soil, and the amount of erosion that occurs. Soil with vegetation that completely covers it for a major portion of the year -- alfalfa and winter cover crops -- will experience less soil erosion than bare soil (Ritter, Jim). This is because the roots of plants absorb water as it flows over land, preventing it from eroding the soil. In addition, the roots of plants hold the soil particles in place, preventing it from being easily eroded by wind or water. Therefore, the loss of vegetation and ground cover due to human activity: deforestation and construction, can have pernicious effects on the environment. Through this lab, the problem: "How does the presence and type of ground cover of soil affect the level of erosion that occurs?" will be addressed.
Pre-Lab Questions
1. Define the following:
Agriculture industries, mining industries, and logging industries would all benefit from knowing the structure of the soil.
3. Using what you know about North Carolina now, would large scale use of septic tanks work well?
The soil of North Carolina mainly consists of clay -- a component of soil with a low permeability to water. According to Hoover, the ideal composition of soil for the construction of septic tanks should be neither “too sandy nor too clayey”. Sites with this soil composition are ideal for the construction of
septic tanks, for they are gently sloping, thick, and permeable, and have deep water tables, which allow for easy downward flow of water.
4. Use the soil triangle to decide what type of soil the following are.
- Porosity: a measure of the amount of holes in a sample of soil
- Permeability: a measure of the ability of a sample of soil to allow fluids to pass through it
- Water-holding Capacity: a measure of the ability of a sample of soil to retain water
- Solution: a homogeneous mixture of two substances
- Suspension: the suspension of small particles in a liquid (water)
Agriculture industries, mining industries, and logging industries would all benefit from knowing the structure of the soil.
3. Using what you know about North Carolina now, would large scale use of septic tanks work well?
The soil of North Carolina mainly consists of clay -- a component of soil with a low permeability to water. According to Hoover, the ideal composition of soil for the construction of septic tanks should be neither “too sandy nor too clayey”. Sites with this soil composition are ideal for the construction of
septic tanks, for they are gently sloping, thick, and permeable, and have deep water tables, which allow for easy downward flow of water.
4. Use the soil triangle to decide what type of soil the following are.
- 10% Clay, 60% Sand, and 30% Silt : Sandy Loam
- 60% Clay, 20% Sand, and 20% Silt : Clay
- 20% Clay, 20% Sand, and 60% Silt : Silt Loam
- 20% Clay, 40% Sand, and 40% Silt : Loam
Hypothesis:
If three samples of soil -- one with no ground cover, the second with small rocks, and the third with grass -- are exposed to flowing water, then the one with no ground cover will have the most erosion, while the one with grass will have the least erosion.
Parts of the Experiment:
- The independent variable consists of the ground cover -- small rocks and grass.
- The dependent variable is the amount of erosion that occurs and the amount of time it takes for the water to flow out of the bottle when it is poured into the bottle.
- The controlled variables are the materials.
- The control group consists of the sample of soil without ground cover.
- The experimental group consists of the samples of soil with small rocks and grass.
Materials:
- 3 empty, cut-open 2 L bottles
- soil
- small rocks
- grass
- 3 blocks of wood
- water
- 1 100 mL beaker
- 1 250 mL beaker
- stopwatch
Methods:
- Obtain 3 empty, cut-open 2 L bottles.
- Fill one bottle up with soil (control).
- Fill the second bottle up with soil and cover the top with small rocks.
- Obtain the third bottle, which is already filled with soil and grass.
- Fill one 250 mL beaker with water.
- Take the caps off of all the bottles.
- Elevate the control sample bottle using a block of wood so that the opening of the bottle is facing the sink (picture 1 under "Experiment").
- Place an empty 100 mL beaker below the opening of the bottle. Pour 250 mL of of water into the sample. Record the amount of time it takes for all the water to flow out of the bottle and into the beaker. Record the color and texture of the water in the beaker.
- Repeat steps 7 and 8 for the samples of soil with small rocks and grass.
Data:
Data Analysis
After having organized the data using a table, it was made clear that the sample with no ground cover (control) had the most erosion in the shortest length of time. This was indicated by the high turbidity of the water collected: The water contained large collections of soil and some organic matter -- mainly leaves (picture 3). In addition, the sample with small rocks had a moderate amount of erosion in a longer length of time than the control sample. This was indicated by the clearness of the water collected: The water contained some sand and particles of soil, however, not as much as the sample of soil with no ground cover (picture 5). Finally, the sample with grass had the least erosion in a longer length of time than the control sample. This was indicated by the clearness of the water collected: The water contained little to no particles of soil (picture 7).
There appears to have been a skew in the data: Out of all three samples, it would have been predicted that the one with no ground cover would absorb the least amount of water, since it lacks plant roots to absorb the water, while the one with grass would absorb the greatest amount water, since it has plant roots to absorb the water. However, the data makes it clear that the sample with no ground cover absorbed about the same amount of water as the sample with small rocks (around 200 mL of water), while the sample with grass absorbed the least amount of water (about 152 mL of water). This is most likely due to a disparity in the amount of water already present in each sample of soil: The sample of soil with vegetation had been watered earlier in the week; on the other hand, the soil with no ground cover had not been watered in a while. As a result, the former may not have been able to retain as much water as the latter, resulting in a greater amount of water collected from the former than from the latter. In order to preclude future skews in the data collected from this experiment, it may be necessary to use soil with the same amount of water present for each sample.
There appears to have been a skew in the data: Out of all three samples, it would have been predicted that the one with no ground cover would absorb the least amount of water, since it lacks plant roots to absorb the water, while the one with grass would absorb the greatest amount water, since it has plant roots to absorb the water. However, the data makes it clear that the sample with no ground cover absorbed about the same amount of water as the sample with small rocks (around 200 mL of water), while the sample with grass absorbed the least amount of water (about 152 mL of water). This is most likely due to a disparity in the amount of water already present in each sample of soil: The sample of soil with vegetation had been watered earlier in the week; on the other hand, the soil with no ground cover had not been watered in a while. As a result, the former may not have been able to retain as much water as the latter, resulting in a greater amount of water collected from the former than from the latter. In order to preclude future skews in the data collected from this experiment, it may be necessary to use soil with the same amount of water present for each sample.
Conclusion:
The results of the experiment supported the hypothesis -- “If three samples of soil, one with no ground cover, one with small rocks, and one with grass, are exposed to flowing water, then the one with no ground cover will have the most erosion, while the one with grass will have the least erosion”. This was indicated by the high turbidity of the water collected from the sample of soil with no ground cover, and the clearness of the water collected from the sample of soil with grass. The water collected from the former contained large collections of soil and some organic matter, while the water collected from the latter contained little to no particles of soil. This experiment further substantiated the hypothesis and reiterated the importance of vegetation in preventing soil erosion, for the sample of soil with small rocks still had a moderate amount of erosion.
This experiment reiterated the importance of ground cover -- specifically vegetation -- in preventing soil erosion. According to Thorpe, vegetation absorbs water as it flows over land, preventing it from eroding the soil. In addition, the roots of plants hold the soil particles in place, preventing it from being easily eroded by wind or water. Therefore, human-related activities that destroy vegetative ground cover expedite the rate of soil erosion. Deforestation is the main human-related activity that expedites the rate of soil erosion: When large forests are burned or clear-cutted, the plant cover of the forests is destroyed, and "Without plant cover, erosion can occur and sweep the land into rivers, ... and as land loses its fertile soil, agricultural producers move on, clear more forest and continue the cycle of soil loss" (Weyerhaeuser, Fredrick). Overgrazing is another human-related activity that expedites the rate of soil erosion: "Overgrazing can reduce ground cover, enabling erosion and compaction of the land by wind and rain.. This reduces the ability for plants to grow and water to penetrate, which harms soil microbes and results in serious erosion of the land" (Weyerhaeuser, Fredrick).
According to Ritter, soil erosion often leads to soil desertification -- the process in which an area becomes a desert. Droughts, arid conditions, infertile soil, loss of biodiversity, and economic costs are all associated with soil desertification; therefore, it is a problem that has to be addressed. Although deforestation will never be completely eliminated, the harmful environmental impacts can be countered by reforestation efforts and forest management; these efforts will help restore the plant cover that is lost as a result of deforestation, therefore, decreasing soil erosion and desertification in that area. Although zero net deforestation is not feasible due to the amount of deforestation that occurs around the globe daily, these efforts will greatly reduce soil erosion and its pernicious effects in the areas in which they are implemented.
This experiment reiterated the importance of ground cover -- specifically vegetation -- in preventing soil erosion. According to Thorpe, vegetation absorbs water as it flows over land, preventing it from eroding the soil. In addition, the roots of plants hold the soil particles in place, preventing it from being easily eroded by wind or water. Therefore, human-related activities that destroy vegetative ground cover expedite the rate of soil erosion. Deforestation is the main human-related activity that expedites the rate of soil erosion: When large forests are burned or clear-cutted, the plant cover of the forests is destroyed, and "Without plant cover, erosion can occur and sweep the land into rivers, ... and as land loses its fertile soil, agricultural producers move on, clear more forest and continue the cycle of soil loss" (Weyerhaeuser, Fredrick). Overgrazing is another human-related activity that expedites the rate of soil erosion: "Overgrazing can reduce ground cover, enabling erosion and compaction of the land by wind and rain.. This reduces the ability for plants to grow and water to penetrate, which harms soil microbes and results in serious erosion of the land" (Weyerhaeuser, Fredrick).
According to Ritter, soil erosion often leads to soil desertification -- the process in which an area becomes a desert. Droughts, arid conditions, infertile soil, loss of biodiversity, and economic costs are all associated with soil desertification; therefore, it is a problem that has to be addressed. Although deforestation will never be completely eliminated, the harmful environmental impacts can be countered by reforestation efforts and forest management; these efforts will help restore the plant cover that is lost as a result of deforestation, therefore, decreasing soil erosion and desertification in that area. Although zero net deforestation is not feasible due to the amount of deforestation that occurs around the globe daily, these efforts will greatly reduce soil erosion and its pernicious effects in the areas in which they are implemented.
Citations:
Hoover, Michael T. "Septic Systems and Their Maintenance." Septic Tanks and Their Maintenance. North Carolina Cooperative Extension Service, Dec. 1997. Web. 30 Oct. 2014.
Ritter, Jim. "Soil Erosion – Causes and Effects." Soil Erosion – Causes and Effects. Queen's Printer for Ontario, 13 Nov. 2013. Web. 26 Oct. 2014. <http://www.omafra.gov.on.ca/english/engineer/facts/12-053.htm>.
Thorpe, Gary S. "The Earth." AP Environmental Science. 5th ed. Hauppauge, NY: Barron's Educational Series, 2013. 93. Print.
Weyerhaeuser, Fredrick. "Soil Erosion and Degradation."WorldWildlife.org. World Wildlife Fund, 2014. Web. 02 Nov. 2014. <http://www.worldwildlife.org/threats/soil-erosion-and-degradation>.
Ritter, Jim. "Soil Erosion – Causes and Effects." Soil Erosion – Causes and Effects. Queen's Printer for Ontario, 13 Nov. 2013. Web. 26 Oct. 2014. <http://www.omafra.gov.on.ca/english/engineer/facts/12-053.htm>.
Thorpe, Gary S. "The Earth." AP Environmental Science. 5th ed. Hauppauge, NY: Barron's Educational Series, 2013. 93. Print.
Weyerhaeuser, Fredrick. "Soil Erosion and Degradation."WorldWildlife.org. World Wildlife Fund, 2014. Web. 02 Nov. 2014. <http://www.worldwildlife.org/threats/soil-erosion-and-degradation>.