Collaborators:
David Delgado, James Hamill, Caroline Knowles and Hannah Whitt.
David Delgado, James Hamill, Caroline Knowles and Hannah Whitt.
Introduction & Problem:
Soil erosion is a naturally occurring process, and it is responsible for creating some of the most majestic landscapes on Earth; however, human intervention expedites these changes by hindering soil formation, making erosion a serious ecological issue. The problem with erosion is twofold — soil health is threatened and nearby water sources become susceptible to pollution by valuable plant nutrients. The effects of this ecological problem can be seen at a local scale. Due to a growing population, the city of Raleigh demands increased crop yields from local farms and more land for housing, which inevitably disrupts the land and exacerbates soil erosion. Thus, the North Carolina Sedimentation Control Law plays a significant role by regulating construction and other land-disturbing activities. This law “prohibits visible off-site sedimentation from construction sites but permits the owner and developer to determine the most economical, effective methods for erosion and sedimentation control”(North Carolina Sedimentation Control Law). Ground cover has been proven to be the most effective method in that it intercepts raindrops to mitigate the destruction of soil structure, and impedes run-off water to give it more time to infiltrate and to allow deposition of sediment. Therefore, ground cover is important in “preserving the productive value of soil and sustaining the quality of the waters that receives the sediment”(Lang, Des and McDonald, G. Warren). However, not all types of ground cover have the same ability to reduce the risk of erosion, which is why it is important to determine the most effective ground cover when it comes to stimulating soil health, plant growth and water quality. For this reason, the question that will be addressed throughout this experiment is, "How does the presence and type of ground cover affect the level of erosion that occurs in an ecosystem?"
Hypothesis:
If three samples of soil — one with grass, the second with small rocks and the third with no ground cover — are exposed to flowing water, then the one with grass will have the least amount of erosion as soil is better protected by plant cover, while the bare soil will have the most erosion due to the lack of protection provided by ground cover.
Parts of the Experiment:
Materials & Methods:
a) Materials:
A. Sowing the seeds
Data & Data Analysis:
a) Data:
Soil erosion is a naturally occurring process, and it is responsible for creating some of the most majestic landscapes on Earth; however, human intervention expedites these changes by hindering soil formation, making erosion a serious ecological issue. The problem with erosion is twofold — soil health is threatened and nearby water sources become susceptible to pollution by valuable plant nutrients. The effects of this ecological problem can be seen at a local scale. Due to a growing population, the city of Raleigh demands increased crop yields from local farms and more land for housing, which inevitably disrupts the land and exacerbates soil erosion. Thus, the North Carolina Sedimentation Control Law plays a significant role by regulating construction and other land-disturbing activities. This law “prohibits visible off-site sedimentation from construction sites but permits the owner and developer to determine the most economical, effective methods for erosion and sedimentation control”(North Carolina Sedimentation Control Law). Ground cover has been proven to be the most effective method in that it intercepts raindrops to mitigate the destruction of soil structure, and impedes run-off water to give it more time to infiltrate and to allow deposition of sediment. Therefore, ground cover is important in “preserving the productive value of soil and sustaining the quality of the waters that receives the sediment”(Lang, Des and McDonald, G. Warren). However, not all types of ground cover have the same ability to reduce the risk of erosion, which is why it is important to determine the most effective ground cover when it comes to stimulating soil health, plant growth and water quality. For this reason, the question that will be addressed throughout this experiment is, "How does the presence and type of ground cover affect the level of erosion that occurs in an ecosystem?"
Hypothesis:
If three samples of soil — one with grass, the second with small rocks and the third with no ground cover — are exposed to flowing water, then the one with grass will have the least amount of erosion as soil is better protected by plant cover, while the bare soil will have the most erosion due to the lack of protection provided by ground cover.
Parts of the Experiment:
- The control group consists of the sample of soil without ground cover.
- The experimental group is constituted by the samples of soil with grass and small rocks.
- The independent variable is the type of ground cover — grass and small rocks
- The dependent variable is the amount of water collected in mL and the time that it takes for the water to stop flowing out of the bottle.
- The controlled variables are the materials, the amount of water poured into each 2L bottle, the angle of elevation of the bottles and relative amount of force exerted by the flow (impact) of the water.
Materials & Methods:
a) Materials:
- 3 - 2 liter bottles, cut in half
- 3- 500 mL beakers
- Potting soil
- Grass seed, fescue plants
- Pebbles, gravel or leaf litter
- Elevated surface to hold the 3 litter bottles
- Water
A. Sowing the seeds
- Place soil in an empty 2L bottle that has been cut in half (see picture above). Spread grass seed evenly throughout the soil.
- Water grass seed every 3-4 days and allow it to sit near a source of sunlight or under a plant grow lamp.
- When the grass has grown 2-4 inches in height, you are ready to test the effects (first 2L bottle).
- Fill two more empty 2L bottles with soil. Cover one with a top cover of your choice (gravel, pebbles, or leaf litter) and leave the other one alone as a control.
- Line the three bottles up on top of an elevated surface. Place an empty beaker underneath the mouth of each bottle.
- Obtain a beaker with 500 mL of water.
- Have a student start a timer and say “GO.” When the timer says go, the water in the beaker should be poured onto the soil bottle.
- Record the time, amount, and color of the water discharge in Table 1.
- Repeat steps 4 - 6 for the samples of soil with small rocks and grass.
- Answer the conclusion questions.
Data & Data Analysis:
a) Data:
Images courtesy of Caroline Knowles
b) Data Analysis:
Three samples of soils — one with grass, the second with small rocks and the third with no ground cover -- were placed in 2 liter bottles and their ability to mitigate soil erosion was tested by pouring the same amount of water (500 mL) into each sample. After organizing the data using a table, it became evident that the grass was the most effective ground cover for minimizing soil erosion. Although the amount of water collected was greater for the sample of soil with grass, the quality of the water supported the fact that plant cover is effective for runoff and erosion control. While the bare soil yielded a water mix with high turbidity and large particles of soil, the sample with grass managed to retain the sediments better by impeding surface run-off and thus yielding a clear water mix. These qualitative observations are conveyed by picture 4, where the sample with grass is on the far left and the sample with only soil is in the middle. The sample with rocks also caused a large amount of water to be collected (350 mL), but it dramatically slowed run-off water to give it more time to infiltrate the soil. In fact, the soil sample with rocks took longer to stop flowing out of the bottle than both of the other samples combined. The quality of the water observed for this sample's mixture could be attributed to the aforementioned factors. Since the rocks hampered the impact of the water on the soil and slowed run-off water, only silt-like substances were eroded and they mixed well with the water. Thus, the sample with the rocks was the second most effective ground cover for minimizing soil erosion.
Conclusions:
The hypothesis — "If three samples of soil, one with grass, the second with small rocks and the third with no ground cover, are exposed to flowing water, then the one with grass will have the least amount of erosion as water is retained better by plant cover, while the bare soil will have the most erosion due to the lack of protection provided by ground cover" — was substantiated by the results of this experiment. It is interesting to note some discrepancies in the data, which at first could only be attributed to possible errors in the actual experiment. The fact that the potting soil was able to retain the most water out of all three samples without the aid of ground cover was astonishing. It was expected that the lack of plant roots to absorb water would cause the sample without ground cover (control) to absorb the least amount of water; however, the data shows that this did not occur. The data demonstrates that the control absorbed more water than the sample of soil with grass, 195 mL more to be exact. This was later attributed to the fact that the soil with plant cover had recently been watered. Thus, the sample with grass had already reached it's water holding capacity and it could not retain any more of the run-off water. On the other hand, the potting soil, according to Hannah Whitt, had not been watered in the past week. In addition, it was later determined that potting soil is designed to "absorb water quickly and retain up to two times its own weight in water"(Balcony Container Gardening). Therefore, the potting soil was able to retain the most amount of water even without the presence of ground cover. Despite these observations, the group's hypothesis was not completely invalidated. The water collected from the control sample proved that soil without ground cover is at a greater risk of erosion; it had large soil particles, some organic matter, and high turbidity. Without plant cover to impede run-off water and facilitate the deposition of sediment, the "soil particles [in the potting soil] can be more easily eroded once they become saturated"(Rudd, P. J). It would certainly help to inhibit these disparities if all soil samples used in the experiment had the same water holding capacity.
The results of this experiment emphasize the importance of plant cover in preventing soil erosion. This is not an attempt to belittle the role of other types of ground cover. However, the data from this experiment shows that vegetation is the most crucial cover to promote soil health, plant growth, and water quality. After deforestation, planting grass seed would create a long-term solution to various ecological issues. It would reduce soil erosion by impeding the impact of raindrops on the soil surface, and more importantly by slowing run-off water to give it more time to infiltrate and to allow deposition of sediment. "Attached plant material is more effective than unattached material (litter) for run-off and erosion control as it is not subject to being carried away in run-off"(Lang, Des, and McDonald, G. Warren). Thus, litter would be effective only if it were not susceptible to run-off, and even then plant cover would be more effective in restoring a habitat to a state of ecological equilibrium. Aside from this, it is important to determine the plant type that will be used. Selecting plant species should be done only after considering the climate, soil and grazing regime of a community so that they will persist, and effectively prevent soil erosion. Water filtration ties along with the ability of run-off water to be slowed by the soil's ground cover. Since the sample with grass slows water run-off, it offers the greatest chance of water filtration. In addition, this ground cover creates barriers that allow sediment in the run-off water to be quickly deposited, meaning that valuable plant nutrients are less likely to pollute water sources and instead they can be deposited in the soil to stimulate plant growth.
Overall, this lab demonstrates the importance of maintaining good ground cover over soil. This premise is further substantiated by experiments conducted on a larger scale. For example, Peter Rudd used a rainfall simulator to demonstrate that ground cover effectively protected the soil by "delaying the start of runoff, reducing the rate of runoff was reduced, reducing the amount of runoff, and
reducing the amount of silt in the runoff water"(Rudd, P.J). In addition, the Hubbard Brook Experiment centered on how deforestation affects nutrient cycles in a larger ecosystem. The control group consisted of the loss of water and nutrients form an uncut forest ecosystem, which would be used to compare to the loss in one that was stripped of its trees. V-shaped concrete dams were built across the creeks, and anchored by impervious bedrock, so that all surface water leaving could be measured along with its dissolved nutrient content. The results showed that when deforestation occurred, water runoff increased. "With no plants to help absorb and retain water, the amount of water flowing out of the deforested valley increased by 30-40%"(Landscape Maintenance - Causes of Erosion).
Consequently, soil erosion increased, which caused a large increase in the outflow of nutrients from the ecosystem. This demonstrates that deforestation is a disastrous process; it results in a degraded environment with reduced biodiversity and reduced ecological services. The pernicious effects of deforestation can only be hindered if efforts are made to ensure that soil has adequate ground
cover, especially vegetation, that will improve its ability to prevent soil erosion.
Citations:
"Landscape Maintenance - Causes of Erosion." Causes of Erosion. Landscape Planet, n.d. Web. 02 Nov. 2014. <http://www.landscapeplanet.com/maintenance-1-cause-of-erosion.htm>.
Lang, Des, and McDonald, G. Warren. Maintaining Groundcover to Reduce Erosion and Sustain Production. Tamworth: NSW Department of Primary Industries, 14 Jan. 2005. PDF.
Norris, Kara. Effects of Erosion Lab. N.p.: Web. 2 Nov. 2014. PDF.
North Carolina Sedimentation Control Law. N.p.: Web. 2 Nov. 2014. NC Department of Environment and Natural Resources, n.d. PDF.
Rudd, P. J. "EFFECT OF GROUND COVER AND REDUCED CULTIVATION ON RUNOFF AND EROSION." The Archives of the Rare Fruit Council of Australia. N.p., Sept. 1987. Web. 02 Nov. 2014. <http://rfcarchives.org.au/Next/CaringForTrees/GroundCoverSoilLoss9-87.htm>.
"What Is Potting Soil?" Balcony Container Gardening. N.p., n.d. Web. 06 Nov. 2014.<http://www.balconycontainergardening.com/gardening/147-what-is-potting-soil>.
Three samples of soils — one with grass, the second with small rocks and the third with no ground cover -- were placed in 2 liter bottles and their ability to mitigate soil erosion was tested by pouring the same amount of water (500 mL) into each sample. After organizing the data using a table, it became evident that the grass was the most effective ground cover for minimizing soil erosion. Although the amount of water collected was greater for the sample of soil with grass, the quality of the water supported the fact that plant cover is effective for runoff and erosion control. While the bare soil yielded a water mix with high turbidity and large particles of soil, the sample with grass managed to retain the sediments better by impeding surface run-off and thus yielding a clear water mix. These qualitative observations are conveyed by picture 4, where the sample with grass is on the far left and the sample with only soil is in the middle. The sample with rocks also caused a large amount of water to be collected (350 mL), but it dramatically slowed run-off water to give it more time to infiltrate the soil. In fact, the soil sample with rocks took longer to stop flowing out of the bottle than both of the other samples combined. The quality of the water observed for this sample's mixture could be attributed to the aforementioned factors. Since the rocks hampered the impact of the water on the soil and slowed run-off water, only silt-like substances were eroded and they mixed well with the water. Thus, the sample with the rocks was the second most effective ground cover for minimizing soil erosion.
Conclusions:
The hypothesis — "If three samples of soil, one with grass, the second with small rocks and the third with no ground cover, are exposed to flowing water, then the one with grass will have the least amount of erosion as water is retained better by plant cover, while the bare soil will have the most erosion due to the lack of protection provided by ground cover" — was substantiated by the results of this experiment. It is interesting to note some discrepancies in the data, which at first could only be attributed to possible errors in the actual experiment. The fact that the potting soil was able to retain the most water out of all three samples without the aid of ground cover was astonishing. It was expected that the lack of plant roots to absorb water would cause the sample without ground cover (control) to absorb the least amount of water; however, the data shows that this did not occur. The data demonstrates that the control absorbed more water than the sample of soil with grass, 195 mL more to be exact. This was later attributed to the fact that the soil with plant cover had recently been watered. Thus, the sample with grass had already reached it's water holding capacity and it could not retain any more of the run-off water. On the other hand, the potting soil, according to Hannah Whitt, had not been watered in the past week. In addition, it was later determined that potting soil is designed to "absorb water quickly and retain up to two times its own weight in water"(Balcony Container Gardening). Therefore, the potting soil was able to retain the most amount of water even without the presence of ground cover. Despite these observations, the group's hypothesis was not completely invalidated. The water collected from the control sample proved that soil without ground cover is at a greater risk of erosion; it had large soil particles, some organic matter, and high turbidity. Without plant cover to impede run-off water and facilitate the deposition of sediment, the "soil particles [in the potting soil] can be more easily eroded once they become saturated"(Rudd, P. J). It would certainly help to inhibit these disparities if all soil samples used in the experiment had the same water holding capacity.
The results of this experiment emphasize the importance of plant cover in preventing soil erosion. This is not an attempt to belittle the role of other types of ground cover. However, the data from this experiment shows that vegetation is the most crucial cover to promote soil health, plant growth, and water quality. After deforestation, planting grass seed would create a long-term solution to various ecological issues. It would reduce soil erosion by impeding the impact of raindrops on the soil surface, and more importantly by slowing run-off water to give it more time to infiltrate and to allow deposition of sediment. "Attached plant material is more effective than unattached material (litter) for run-off and erosion control as it is not subject to being carried away in run-off"(Lang, Des, and McDonald, G. Warren). Thus, litter would be effective only if it were not susceptible to run-off, and even then plant cover would be more effective in restoring a habitat to a state of ecological equilibrium. Aside from this, it is important to determine the plant type that will be used. Selecting plant species should be done only after considering the climate, soil and grazing regime of a community so that they will persist, and effectively prevent soil erosion. Water filtration ties along with the ability of run-off water to be slowed by the soil's ground cover. Since the sample with grass slows water run-off, it offers the greatest chance of water filtration. In addition, this ground cover creates barriers that allow sediment in the run-off water to be quickly deposited, meaning that valuable plant nutrients are less likely to pollute water sources and instead they can be deposited in the soil to stimulate plant growth.
Overall, this lab demonstrates the importance of maintaining good ground cover over soil. This premise is further substantiated by experiments conducted on a larger scale. For example, Peter Rudd used a rainfall simulator to demonstrate that ground cover effectively protected the soil by "delaying the start of runoff, reducing the rate of runoff was reduced, reducing the amount of runoff, and
reducing the amount of silt in the runoff water"(Rudd, P.J). In addition, the Hubbard Brook Experiment centered on how deforestation affects nutrient cycles in a larger ecosystem. The control group consisted of the loss of water and nutrients form an uncut forest ecosystem, which would be used to compare to the loss in one that was stripped of its trees. V-shaped concrete dams were built across the creeks, and anchored by impervious bedrock, so that all surface water leaving could be measured along with its dissolved nutrient content. The results showed that when deforestation occurred, water runoff increased. "With no plants to help absorb and retain water, the amount of water flowing out of the deforested valley increased by 30-40%"(Landscape Maintenance - Causes of Erosion).
Consequently, soil erosion increased, which caused a large increase in the outflow of nutrients from the ecosystem. This demonstrates that deforestation is a disastrous process; it results in a degraded environment with reduced biodiversity and reduced ecological services. The pernicious effects of deforestation can only be hindered if efforts are made to ensure that soil has adequate ground
cover, especially vegetation, that will improve its ability to prevent soil erosion.
Citations:
"Landscape Maintenance - Causes of Erosion." Causes of Erosion. Landscape Planet, n.d. Web. 02 Nov. 2014. <http://www.landscapeplanet.com/maintenance-1-cause-of-erosion.htm>.
Lang, Des, and McDonald, G. Warren. Maintaining Groundcover to Reduce Erosion and Sustain Production. Tamworth: NSW Department of Primary Industries, 14 Jan. 2005. PDF.
Norris, Kara. Effects of Erosion Lab. N.p.: Web. 2 Nov. 2014. PDF.
North Carolina Sedimentation Control Law. N.p.: Web. 2 Nov. 2014. NC Department of Environment and Natural Resources, n.d. PDF.
Rudd, P. J. "EFFECT OF GROUND COVER AND REDUCED CULTIVATION ON RUNOFF AND EROSION." The Archives of the Rare Fruit Council of Australia. N.p., Sept. 1987. Web. 02 Nov. 2014. <http://rfcarchives.org.au/Next/CaringForTrees/GroundCoverSoilLoss9-87.htm>.
"What Is Potting Soil?" Balcony Container Gardening. N.p., n.d. Web. 06 Nov. 2014.<http://www.balconycontainergardening.com/gardening/147-what-is-potting-soil>.